We introduce a mathematical framework for statistical exoplanet population and astrobiology studies
that may help directing future observational efforts and experiments. The approach is based on a
set of differential equations and provides a time-dependent mapping between star formation, metal
enrichment, and the occurrence of exoplanets and potentially life-harboring worlds over the chemopopulation history of the solar neighborhood. Our results are summarized as follows: 1) the formation
of exoplanets in the solar vicinity was episodic, starting with the emergence of the thick disk about
11 Gyr ago; 2) within 100 pc from the Sun, there are as many as 11, 000 (η⊕/0.24) Earth-size planets
in the habitable zone (“temperate terrestrial planets” or TTPs) of K-type stars. The solar system is
younger than the median TTP, and was created in a star formation surge that peaked 5.5 Gyr ago and
was triggered by an external agent; 3) the metallicity modulation of the giant planet occurrence rate
results in a later typical formation time, with TTPs outnumbering giant planets at early times; 4) the
closest, life-harboring Earth-like planet would be ∼
< 20 pc away if microbial life arose as soon as it did
on Earth in ∼
> 1% of the TTPs around K stars. If simple life is abundant (fast abiogenesis), it is also
old, as it would have emerged more than 8 Gyr ago in about one third of all life-bearing planets today.
Older Earth analogs are more likely to have developed sufficiently complex life capable of altering the
environment and producing detectable oxygenic biosignatures.
This document summarizes evidence that submillimeter galaxies (SMGs) at redshift 3-6 may be progenitors of compact quiescent galaxies observed at redshift 2. It compares properties of a sample of z~2 quiescent galaxies with a statistical sample of z>3 SMGs in the COSMOS field. It finds that the formation redshifts of the z~2 galaxies match the observed redshift distribution of z>3 SMGs. It also finds that the space densities and properties such as sizes, stellar masses, and internal velocities of the two populations are consistent with an evolutionary connection, assuming SMG starbursts have a duty cycle of 42+40 Myr. This suggests SMGs may represent an early burst
Four new planets_around_giant_stars_and_the_mass_metallicity_correlation_of_p...Sérgio Sacani
Exoplanet searches have revealed interesting correlations between the stellar properties and the occurrence rate of planets.
In particular, different independent surveys have demonstrated that giant planets are preferentially found around metal-rich stars and
that their fraction increases with the stellar mass.
Aims. During the past six years, we have conducted a radial velocity follow-up program of 166 giant stars, to detect substellar
companions, and characterizing their orbital properties. Using this information, we aim to study the role of the stellar evolution in
the orbital parameters of the companions, and to unveil possible correlations between the stellar properties and the occurrence rate of
giant planets.
Methods. We have taken multi-epoch spectra using FEROS and CHIRON for all of our targets, from which we have computed
precision radial velocities and we have derived atmospheric and physical parameters. Additionally, velocities computed from UCLES
spectra are presented here. By studying the periodic radial velocity signals, we have detected the presence of several substellar
companions.
Results. We present four new planetary systems around the giant stars HIP8541, HIP74890, HIP84056 and HIP95124. Additionally,
we study the correlation between the occurrence rate of giant planets with the stellar mass and metallicity of our targets. We find that
giant planets are more frequent around metal-rich stars, reaching a peak in the detection of f = 16.7+15.5
−5.9 % around stars with [Fe/H] ∼
0.35 dex. Similarly, we observe a positive correlation of the planet occurrence rate with the stellar mass, between M⋆∼ 1.0 - 2.1 M⊙ ,
with a maximum of f = 13.0+10.1
−4.2 %, at M⋆= 2.1 M⊙ .
Conclusions. We conclude that giant planets are preferentially formed around metal-rich stars. Also, we conclude that they are more
efficiently formed around more massive stars, in the stellar mass range of ∼ 1.0 - 2.1 M⊙ . These observational results confirm previous
findings for solar-type and post-MS hosting stars, and provide further support to the core-accretion formation model.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
La historia de la vida en la Tierra y en otras plataformas planetarios potenciales portadoras de vida están profundamente ligadas a la historia del Universo. Puesto que la vida, tal como la conocemos, se basa en elementos químicos forjados en estrellas pesadas moribundas, el Universo tiene que ser lo suficientemente antiguo para que las estrellas se formaran y evolucionaran. La teoría cosmológica actual indica que el Universo es de 13,7 ± 0,13 mil millones de años y que las primeras estrellas se formaron cientos de millones de años después del Big Bang. En este trabajo, se argumenta que podemos dividir la historia cosmológica en cuatro edades, desde el Big Bang a la vida inteligente.
TOI-5678 b: A 48-day transiting Neptune-mass planet characterized with CHEOPS...Sérgio Sacani
A large sample of long-period giant planets has been discovered thanks to long-term radial velocity surveys, but only a few
dozen of these planets have a precise radius measurement. Transiting gas giants are crucial targets for the study of atmospheric composition across a wide range of equilibrium temperatures and, more importantly, for shedding light on the formation and evolution
of planetary systems. Indeed, compared to hot Jupiters, the atmospheric properties and orbital parameters of cooler gas giants are
unaltered by intense stellar irradiation and tidal effects.
Aims. We aim to identify long-period planets in the Transiting Exoplanet Survey Satellite (TESS) data as single or duo-transit events.
Our goal is to solve the orbital periods of TESS duo-transit candidates with the use of additional space-based photometric observations
and to collect follow-up spectroscopic observations in order to confirm the planetary nature and measure the mass of the candidates.
Methods. We use the CHaracterising ExOPlanet Satellite (CHEOPS) to observe the highest-probability period aliases in order to discard or confirm a transit event at a given period. Once a period is confirmed, we jointly model the TESS and CHEOPS light curves
along with the radial velocity datasets to measure the orbital parameters of the system and obtain precise mass and radius measurements.
Results. We report the discovery of a long-period transiting Neptune-mass planet orbiting the G7-type star TOI-5678. Our spectroscopic analysis shows that TOI-5678 is a star with a solar metallicity. The TESS light curve of TOI-5678 presents two transit events
separated by almost two years. In addition, CHEOPS observed the target as part of its Guaranteed Time Observation program. After
four non-detections corresponding to possible periods, CHEOPS detected a transit event matching a unique period alias. Follow-up
radial velocity observations were carried out with the ground-based high-resolution spectrographs CORALIE and HARPS. Joint modeling reveals that TOI-5678 hosts a 47.73 day period planet, and we measure an orbital eccentricity consistent with zero at 2σ. The
planet TOI-5678 b has a mass of 20 ± 4 Earth masses (M⊕) and a radius of 4.91 ± 0.08 R⊕. Using interior structure modeling, we find
that TOI-5678 b is composed of a low-mass core surrounded by a large H/He layer with a mass of 3.2
+1.7
−1.3 M⊕.
Conclusions. TOI-5678 b is part of a growing sample of well-characterized transiting gas giants receiving moderate amounts of stellar
insolation (11 S ⊕). Precise density measurement gives us insight into their interior composition, and the objects orbiting bright stars
are suitable targets to study the atmospheric composition of cooler gas giants.
This pilot survey used modest aperture telescopes to image 8 nearby spiral galaxies in order to search for stellar tidal streams. Ultra-deep imaging revealed 6 previously undetected extensive (up to 30 kpc) stellar structures likely from tidally disrupted satellites. A diversity of tidal feature morphologies was found, including great circle-like streams, remote shells, and jets emerging from disks. Simulations predict tidal debris should be common and match the observed variety, providing evidence minor mergers have shaped disk galaxies since z=1.
1. The document discusses the quest to detect extra-terrestrial life and the consequences this would have for science and society. It explores both the scientific and societal implications.
2. While only life on Earth is currently known, conditions suitable for harboring life are thought to exist on other worlds like Mars, Europa, and Enceladus. The discovery of life elsewhere would have fundamental impacts and challenge existing views of life's uniqueness.
3. There is much unknown about the origin and distribution of life in the universe. Key questions remain unanswered about whether life follows universal principles or if Earth's life arose from highly improbable chances. Detecting life elsewhere could help answer these questions.
Tidal star-planet interaction and its observed impact on stellar activity in ...Sérgio Sacani
This study investigates tidal star-planet interaction by analyzing X-ray observations of planet-hosting stars that are part of wide binary systems. The study compares the X-ray luminosity, an indicator of stellar activity, between the planet-hosting primary star and its non-planet hosting companion star. By analyzing 34 such binary systems with X-ray data from XMM-Newton and Chandra, the study finds that planet hosts with close-in massive planets have higher X-ray luminosity compared to their companion stars, indicating tidal interaction is altering the rotation and magnetic activity of the host stars. The study concludes tidal interaction from massive, close-in planets can impact the rotational evolution of stars, while more distant or smaller planets likely
This document summarizes evidence that submillimeter galaxies (SMGs) at redshift 3-6 may be progenitors of compact quiescent galaxies observed at redshift 2. It compares properties of a sample of z~2 quiescent galaxies with a statistical sample of z>3 SMGs in the COSMOS field. It finds that the formation redshifts of the z~2 galaxies match the observed redshift distribution of z>3 SMGs. It also finds that the space densities and properties such as sizes, stellar masses, and internal velocities of the two populations are consistent with an evolutionary connection, assuming SMG starbursts have a duty cycle of 42+40 Myr. This suggests SMGs may represent an early burst
Four new planets_around_giant_stars_and_the_mass_metallicity_correlation_of_p...Sérgio Sacani
Exoplanet searches have revealed interesting correlations between the stellar properties and the occurrence rate of planets.
In particular, different independent surveys have demonstrated that giant planets are preferentially found around metal-rich stars and
that their fraction increases with the stellar mass.
Aims. During the past six years, we have conducted a radial velocity follow-up program of 166 giant stars, to detect substellar
companions, and characterizing their orbital properties. Using this information, we aim to study the role of the stellar evolution in
the orbital parameters of the companions, and to unveil possible correlations between the stellar properties and the occurrence rate of
giant planets.
Methods. We have taken multi-epoch spectra using FEROS and CHIRON for all of our targets, from which we have computed
precision radial velocities and we have derived atmospheric and physical parameters. Additionally, velocities computed from UCLES
spectra are presented here. By studying the periodic radial velocity signals, we have detected the presence of several substellar
companions.
Results. We present four new planetary systems around the giant stars HIP8541, HIP74890, HIP84056 and HIP95124. Additionally,
we study the correlation between the occurrence rate of giant planets with the stellar mass and metallicity of our targets. We find that
giant planets are more frequent around metal-rich stars, reaching a peak in the detection of f = 16.7+15.5
−5.9 % around stars with [Fe/H] ∼
0.35 dex. Similarly, we observe a positive correlation of the planet occurrence rate with the stellar mass, between M⋆∼ 1.0 - 2.1 M⊙ ,
with a maximum of f = 13.0+10.1
−4.2 %, at M⋆= 2.1 M⊙ .
Conclusions. We conclude that giant planets are preferentially formed around metal-rich stars. Also, we conclude that they are more
efficiently formed around more massive stars, in the stellar mass range of ∼ 1.0 - 2.1 M⊙ . These observational results confirm previous
findings for solar-type and post-MS hosting stars, and provide further support to the core-accretion formation model.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
La historia de la vida en la Tierra y en otras plataformas planetarios potenciales portadoras de vida están profundamente ligadas a la historia del Universo. Puesto que la vida, tal como la conocemos, se basa en elementos químicos forjados en estrellas pesadas moribundas, el Universo tiene que ser lo suficientemente antiguo para que las estrellas se formaran y evolucionaran. La teoría cosmológica actual indica que el Universo es de 13,7 ± 0,13 mil millones de años y que las primeras estrellas se formaron cientos de millones de años después del Big Bang. En este trabajo, se argumenta que podemos dividir la historia cosmológica en cuatro edades, desde el Big Bang a la vida inteligente.
TOI-5678 b: A 48-day transiting Neptune-mass planet characterized with CHEOPS...Sérgio Sacani
A large sample of long-period giant planets has been discovered thanks to long-term radial velocity surveys, but only a few
dozen of these planets have a precise radius measurement. Transiting gas giants are crucial targets for the study of atmospheric composition across a wide range of equilibrium temperatures and, more importantly, for shedding light on the formation and evolution
of planetary systems. Indeed, compared to hot Jupiters, the atmospheric properties and orbital parameters of cooler gas giants are
unaltered by intense stellar irradiation and tidal effects.
Aims. We aim to identify long-period planets in the Transiting Exoplanet Survey Satellite (TESS) data as single or duo-transit events.
Our goal is to solve the orbital periods of TESS duo-transit candidates with the use of additional space-based photometric observations
and to collect follow-up spectroscopic observations in order to confirm the planetary nature and measure the mass of the candidates.
Methods. We use the CHaracterising ExOPlanet Satellite (CHEOPS) to observe the highest-probability period aliases in order to discard or confirm a transit event at a given period. Once a period is confirmed, we jointly model the TESS and CHEOPS light curves
along with the radial velocity datasets to measure the orbital parameters of the system and obtain precise mass and radius measurements.
Results. We report the discovery of a long-period transiting Neptune-mass planet orbiting the G7-type star TOI-5678. Our spectroscopic analysis shows that TOI-5678 is a star with a solar metallicity. The TESS light curve of TOI-5678 presents two transit events
separated by almost two years. In addition, CHEOPS observed the target as part of its Guaranteed Time Observation program. After
four non-detections corresponding to possible periods, CHEOPS detected a transit event matching a unique period alias. Follow-up
radial velocity observations were carried out with the ground-based high-resolution spectrographs CORALIE and HARPS. Joint modeling reveals that TOI-5678 hosts a 47.73 day period planet, and we measure an orbital eccentricity consistent with zero at 2σ. The
planet TOI-5678 b has a mass of 20 ± 4 Earth masses (M⊕) and a radius of 4.91 ± 0.08 R⊕. Using interior structure modeling, we find
that TOI-5678 b is composed of a low-mass core surrounded by a large H/He layer with a mass of 3.2
+1.7
−1.3 M⊕.
Conclusions. TOI-5678 b is part of a growing sample of well-characterized transiting gas giants receiving moderate amounts of stellar
insolation (11 S ⊕). Precise density measurement gives us insight into their interior composition, and the objects orbiting bright stars
are suitable targets to study the atmospheric composition of cooler gas giants.
This pilot survey used modest aperture telescopes to image 8 nearby spiral galaxies in order to search for stellar tidal streams. Ultra-deep imaging revealed 6 previously undetected extensive (up to 30 kpc) stellar structures likely from tidally disrupted satellites. A diversity of tidal feature morphologies was found, including great circle-like streams, remote shells, and jets emerging from disks. Simulations predict tidal debris should be common and match the observed variety, providing evidence minor mergers have shaped disk galaxies since z=1.
1. The document discusses the quest to detect extra-terrestrial life and the consequences this would have for science and society. It explores both the scientific and societal implications.
2. While only life on Earth is currently known, conditions suitable for harboring life are thought to exist on other worlds like Mars, Europa, and Enceladus. The discovery of life elsewhere would have fundamental impacts and challenge existing views of life's uniqueness.
3. There is much unknown about the origin and distribution of life in the universe. Key questions remain unanswered about whether life follows universal principles or if Earth's life arose from highly improbable chances. Detecting life elsewhere could help answer these questions.
Tidal star-planet interaction and its observed impact on stellar activity in ...Sérgio Sacani
This study investigates tidal star-planet interaction by analyzing X-ray observations of planet-hosting stars that are part of wide binary systems. The study compares the X-ray luminosity, an indicator of stellar activity, between the planet-hosting primary star and its non-planet hosting companion star. By analyzing 34 such binary systems with X-ray data from XMM-Newton and Chandra, the study finds that planet hosts with close-in massive planets have higher X-ray luminosity compared to their companion stars, indicating tidal interaction is altering the rotation and magnetic activity of the host stars. The study concludes tidal interaction from massive, close-in planets can impact the rotational evolution of stars, while more distant or smaller planets likely
The Gaia-ESO Survey: Empirical estimates of stellar ages from lithium equival...Sérgio Sacani
We present an empirical model of age-dependent photospheric lithium depletion, calibrated using a large, homogeneouslyanalysed sample of 6200 stars in 52 open clusters, with ages from 2–6000Myr and −0.3 < [Fe/H] < 0.2, observed in the
Gaia-ESO spectroscopic survey. The model is used to obtain age estimates and posterior age probability distributions from
measurements of the Li I 6708Å equivalent width for individual (pre) main sequence stars with 3000 < Teff/K < 6500,
a domain where age determination from the HR diagram is either insensitive or highly model-dependent. In the best cases,
precisions of 0.1 dex in log age are achievable; even higher precision can be obtained for coeval groups and associations where
the individual age probabilities of their members can be combined. The method is validated on a sample of exoplanet-hosting
young stars, finding agreement with claimed young ages for some, but not others. We obtain better than 10 per cent precision
in age, and excellent agreement with published ages, for seven well-studied young moving groups. The derived ages for young
clusters (< 1 Gyr) in our sample are also in good agreement with their training ages, and consistent with several published,
model-insensitive lithium depletion boundary ages. For older clusters there remain systematic age errors that could be as large
as a factor of two. There is no evidence to link these errors to any strong systematic metallicity dependence of (pre) main
sequence lithium depletion, at least in the range −0.29 < [Fe/H] < 0.18. Our methods and model are provided as software –
"Empirical AGes from Lithium Equivalent widthS" (EAGLES).
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
Know the star_know_the_planet_discovery_of_l_ate_type_companions_to_two_exopl...Sérgio Sacani
This document summarizes the discovery of additional late-type stellar companions to two exoplanet host stars, HD 2638 and 30 Ari B, using adaptive optics imaging. For both systems, the companions were found to share common proper motion with the primaries, indicating they are physically associated. The estimated orbital periods of the new companions are 130 years for HD 2638 and 80 years for 30 Ari B. This makes 30 Ari B the second confirmed quadruple star system known to host an exoplanet. The discoveries provide additional examples of how binary companions can influence exoplanet dynamics and formation.
This study analyzed high-resolution spectra of 125 compact stellar systems (CSSs) in the giant elliptical galaxy NGC 5128 to measure their radial velocities and velocity dispersions. Combining these measurements with structural parameters from imaging, dynamical masses were derived for 112 CSSs, including 89 for the first time. Two distinct sequences were found in the dynamical mass-to-light ratio vs dynamical mass plane, which can be approximated by power laws. The shallower sequence corresponds to bright globular clusters, while the steeper relation appears to be populated by objects requiring significant dark matter such as central black holes or concentrated dark matter. This suggests different formation histories for these CSSs compared to classical globular clusters in NGC 5128 and
This document outlines an Earth science curriculum for grades 1-5. It includes 9 units of study for each grade level with performance expectations aligned to disciplinary core ideas and science practices. The units cover topics like Earth's place in the universe and solar system, plate tectonics, weather and climate, and natural resources. Appendices provide templates for proficiency scales and curriculum refinement.
The SPHERE view of three interacting twin disc systems in polarised lightSérgio Sacani
Dense stellar environments as hosts of ongoing star formation increase the probability of gravitational encounters among stellar
systems during the early stages of evolution. Stellar interaction may occur through non-recurring, hyperbolic or parabolic passages
(a so-called ‘fly-by’), through secular binary evolution, or through binary capture. In all three scenarios, the strong gravitational
perturbation is expected to manifest itself in the disc structures around the individual stars. Here, we present near-infrared
polarised light observations that were taken with the SPHERE/IRDIS instrument of three known interacting twin-disc systems:
AS 205, EM* SR 24, and FU Orionis. The scattered light exposes spirals likely caused by the gravitational interaction. On
a larger scale, we observe connecting filaments between the stars. We analyse their very complex polarised intensity and put
particular attention to the presence of multiple light sources in these systems. The local angle of linear polarisation indicates
the source whose light dominates the scattering process from the bridging region between the two stars. Further, we show
that the polarised intensity from scattering with multiple relevant light sources results from an incoherent summation of the
individuals’ contribution. This can produce nulls of polarised intensity in an image, as potentially observed in AS 205.We discuss
the geometry and content of the systems by comparing the polarised light observations with other data at similar resolution,
namely with ALMA continuum and gas emission. Collective observational data can constrain the systems’ geometry and stellar
trajectories, with the important potential to differentiate between dynamical scenarios of stellar interaction.
The Dynamical Consequences of a Super-Earth in the Solar SystemSérgio Sacani
Placing the architecture of the solar system within the broader context of planetary architectures is one of the
primary topics of interest within planetary science. Exoplanet discoveries have revealed a large range of system
architectures, many of which differ substantially from the solar system’s model. One particular feature of exoplanet
demographics is the relative prevalence of super-Earth planets, for which the solar system lacks a suitable analog,
presenting a challenge to modeling their interiors and atmospheres. Here we present the results of a large suite of
dynamical simulations that insert a hypothetical planet in the mass range 1–10 M⊕ within the semimajor axis range
2–4 au, between the orbits of Mars and Jupiter. We show that, although the system dynamics remain largely
unaffected when the additional planet is placed near 3 au, Mercury experiences substantial instability when the
additional planet lies in the range 3.1–4.0 au, and perturbations to the Martian orbit primarily result when the
additional planet lies in the range 2.0–2.7 au. We further show that, although Jupiter and Saturn experience
relatively small orbital perturbations, the angular momentum transferred to the ice giants can result in their ejection
from the system at key resonance locations of the additional planet. We discuss the implications of these results for
the architecture of the inner and outer solar system planets, and for exoplanetary systems
X-Ray-luminous Supernovae: Threats to Terrestrial BiospheresSérgio Sacani
The spectacular outbursts of energy associated with supernovae (SNe) have long motivated research into their
potentially hazardous effects on Earth and analogous environments. Much of this research has focused primarily on
the atmospheric damage associated with the prompt arrival of ionizing photons within days or months of the initial
outburst, and the high-energy cosmic rays that arrive thousands of years after the explosion. In this study, we turn
the focus to persistent X-ray emission, arising in certain SNe that have interactions with a dense circumstellar
medium and observed months and/or years after the initial outburst. The sustained high X-ray luminosity leads to
large doses of ionizing radiation out to formidable distances. We assess the threat posed by these X-ray-luminous
SNe for Earth-like planetary atmospheres; our results are rooted in the X-ray SN observations from Chandra, Swift-
XRT, XMM-Newton, NuSTAR, and others. We find that this threat is particularly acute for SNe showing evidence
of strong circumstellar interaction, such as Type IIn explosions, which have significantly larger ranges of influence
than previously expected and lethal consequences up to ∼50 pc away. Furthermore, X-ray-bright SNe could pose a
substantial and distinct threat to terrestrial biospheres and tighten the Galactic habitable zone. We urge follow-up
X-ray observations of interacting SNe for months and years after the explosion to shed light on the physical nature
and full-time evolution of the emission and to clarify the danger that these events pose for life in our galaxy and
other star-forming regions.
We present the 2020 version of the Siena Galaxy Atlas (SGA-2020), a multiwavelength optical and infrared
imaging atlas of 383,620 nearby galaxies. The SGA-2020 uses optical grz imaging over ≈20,000 deg2 from the
Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys Data Release 9 and infrared imaging in
four bands (spanning 3.4–22 μm) from the 6 year unWISE coadds; it is more than 95% complete for galaxies larger
than R(26) ≈ 25″ and r < 18 measured at the 26 mag arcsec−2 isophote in the r band. The atlas delivers precise
coordinates, multiwavelength mosaics, azimuthally averaged optical surface-brightness profiles, model images and
photometry, and additional ancillary metadata for the full sample. Coupled with existing and forthcoming optical
spectroscopy from the DESI, the SGA-2020 will facilitate new detailed studies of the star formation and mass
assembly histories of nearby galaxies; enable precise measurements of the local velocity field via the Tully–Fisher
and fundamental plane relations; serve as a reference sample of lasting legacy value for time-domain and
multimessenger astronomical events; and more.
A Search for Technosignatures Around 11,680 Stars with the Green Bank Telesco...Sérgio Sacani
We conducted a search for narrowband radio signals over four observing sessions in 2020–2023 with
the L-band receiver (1.15–1.73 GHz) of the 100 m diameter Green Bank Telescope. We pointed the
telescope in the directions of 62 TESS Objects of Interest, capturing radio emissions from a total of
∼11,860 stars and planetary systems in the ∼9 arcminute beam of the telescope. All detections were
either automatically rejected or visually inspected and confirmed to be of anthropogenic nature. In
this work, we also quantified the end-to-end efficiency of radio SETI pipelines with a signal injection
and recovery analysis. The UCLA SETI pipeline recovers 94.0% of the injected signals over the usable
frequency range of the receiver and 98.7% of the injections when regions of dense RFI are excluded. In
another pipeline that uses incoherent sums of 51 consecutive spectra, the recovery rate is ∼15 times
smaller at ∼6%. The pipeline efficiency affects SETI search volume calculations as well as calculations
of upper bounds on the number of transmitting civilizations. We developed an improved Drake Figure
of Merit for SETI search volume calculations that includes the pipeline efficiency and frequency drift
rate coverage. Based on our observations, we found that there is a high probability (94.0–98.7%) that
fewer than ∼0.014% of stars earlier than M8 within 100 pc host a transmitter that is detectable in
our search (EIRP > 1012 W). Finally, we showed that the UCLA SETI pipeline natively detects the
signals detected with AI techniques by Ma et al. (2023).
The Variable Detection of Atmospheric Escape around the Young, Hot Neptune AU...Sérgio Sacani
This document summarizes observations from the Hubble Space Telescope of the young hot Neptune exoplanet AU Mic b, which orbits the nearby M dwarf star AU Mic. The observations aimed to detect atmospheric escape of neutral hydrogen through absorption in the stellar Lyman-alpha emission line. Two visits were obtained, one in 2020 and one in 2021, corresponding to transits of the planet. A stellar flare was observed and removed from the first visit data. In the second visit, absorption was detected in the blue wing of the Lyman-alpha line 2.5 hours before the white light transit, indicating the presence of high-velocity neutral hydrogen escaping the planet's atmosphere and traveling toward the observer. Estimates place the column density of this material
The document provides an overview of the field of astrobiology, including its history and goals. It discusses the search for life on Mars, Europa and beyond Earth. The goals of astrobiology include understanding the origin and distribution of life, characterizing habitable environments in the solar system and beyond, and determining how life emerges and evolves in different environments. Both long term goals like searching for life on other worlds and short term goals like Mars exploration are mentioned.
Large-scale Volcanism and the Heat Death of Terrestrial WorldsSérgio Sacani
This document discusses the potential for large igneous provinces (LIPs) to cause the "heat death" of terrestrial planets through massive volcanic eruptions that overwhelm the climate system. It examines the timing of LIP events on Earth to estimate the likelihood of nearly simultaneous eruptions. Statistical analysis of Earth's LIP record finds that eruptions within 0.1-1 million years of each other are likely. Simultaneous LIPs could have driven Venus into a runaway greenhouse effect like its current state. The timing of LIP events on Earth provides insight into potential past LIP activity on Venus that may have ended its hypothesized earlier temperate climate.
This document describes a model of crater formation on the Moon and terrestrial planets based on the current understanding of the impactor population in the inner Solar System. The model calculates impact rates spatially across planetary surfaces to account for nonuniform cratering. It finds that the lunar cratering rate varies with latitude and longitude, being about 25% lower in some regions and higher in others. The model reconciles measured lunar crater size-frequency distributions with observations of near-Earth objects, assuming the presence of a porous lunar megaregolith affects the size of small craters. It provides revised estimates of the ages of some lunar and planetary geological features based on crater counts and the derived crater chronology.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
The vvv survey_reveals_classical_cepheids_tracing_a_young_and_thin_stellar_di...Sérgio Sacani
Com o auxílio do telescópio VISTA instalado no Observatório do Paranal do ESO, astrônomos descobriram uma componente anteriormente desconhecida da Via Láctea. Ao mapear a localização de uma classe de estrelas que variam em brilho chamadas Cefeidas, foi descoberto um disco de estrelas jovens enterradas por trás de espessas nuvens de poeira no bojo central.
O rastreio público do ESO VISTA Variables in the Vía Láctea (VVV) [1] usa o telescópio VISTA instalado no Observatório do Paranal para obter imagens múltiplas em épocas diferentes das regiões centrais da nossa Galáxia nos comprimentos de onda do infravermelho [2]. O rastreio está descobrindo uma enorme quantidade de novos objetos, incluindo estrelas variáveis, aglomerados e estrelas em explosão (eso1101, eso1128, eso1141).
Uma equipe de astrônomos, liderada por Istvan Dékány da Pontificia Universidad Católica de Chile, utilizou dados deste rastreio, obtidos entre 2010 e 2014, para fazer uma descoberta notável — um componente anteriormente desconhecido da Via Láctea, a Galáxia que nos acolhe.
Kinematics and simulations_of_the_stellar_stream_in_the_halo_of_the_umbrella_...Sérgio Sacani
This document summarizes a study of the stellar stream and substructures around the Umbrella Galaxy (NGC 4651). Deep imaging and spectroscopy were used to characterize the properties and kinematics of the stream. Tracer objects like globular clusters and planetary nebulae were identified and found to delineate a kinematically cold feature in position-velocity space. Dynamical modeling suggests the stream originated from the tidal disruption of a dwarf galaxy on a highly eccentric orbit about 6-10 billion years ago. This work demonstrates the feasibility of using discrete tracers to recover the kinematics and model the dynamics of low surface brightness stellar streams around distant galaxies.
Exploring the nature and synchronicity of early cluster formation in the Larg...Sérgio Sacani
We analyse Hubble Space Telescope observations of six globular clusters in the Large Magel- lanic Cloud (LMC) from programme GO-14164 in Cycle 23. These are the deepest available observations of the LMC globular cluster population; their uniformity facilitates a precise comparison with globular clusters in the Milky Way. Measuring the magnitude of the main- sequence turn-off point relative to template Galactic globular clusters allows the relative ages of the clusters to be determined with a mean precision of 8.4 per cent, and down to 6 per cent for individual objects. We find that the mean age of our LMC cluster ensemble is identical to the mean age of the oldest metal-poor clusters in the Milky Way halo to 0.2 ± 0.4 Gyr. This provides the most sensitive test to date of the synchronicity of the earliest epoch of globular cluster formation in two independent galaxies. Horizontal branch magnitudes and subdwarf fitting to the main sequence allow us to determine distance estimates for each cluster and examine their geometric distribution in the LMC. Using two different methods, we find an average distance to the LMC of 18.52 ± 0.05.
The document analyzes the merger fractions of radio-loud and radio-quiet active galactic nuclei (AGN) at z > 1 using new Hubble Space Telescope (HST) samples. It finds that 92% (+8%/-14%) of radio-loud galaxies at z > 1 show evidence of recent or ongoing mergers, while only 38% (+16%/-15%) of matched radio-quiet samples exhibit mergers. This provides strong evidence that mergers are the triggering mechanism for radio-loud AGN phenomena like relativistic jet launching, and that major black hole mergers may spin up central supermassive black holes in these objects.
The document discusses current research in the field of astrobiology. It covers research being done on Mars, Enceladus, and Titan to discover evidence of ancient or current life. On Mars, methane pulses detected by the Curiosity rover could potentially be produced by methanogens living underground. Enceladus shows signs of hydrothermal activity and a subsurface ocean, conditions that could support life. Titan, with its liquid hydrocarbon seas, may be able to support a hypothetical form of life called an azotosome, which could use nitrogen-based membranes instead of cell walls. The document argues that expanding our understanding of possible forms life could take is important for continuing progress in the search for life beyond Earth.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
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Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
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often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
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emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
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(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
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is very small (< 0.00003–0.002). We propose that the lack
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This document summarizes the discovery of additional late-type stellar companions to two exoplanet host stars, HD 2638 and 30 Ari B, using adaptive optics imaging. For both systems, the companions were found to share common proper motion with the primaries, indicating they are physically associated. The estimated orbital periods of the new companions are 130 years for HD 2638 and 80 years for 30 Ari B. This makes 30 Ari B the second confirmed quadruple star system known to host an exoplanet. The discoveries provide additional examples of how binary companions can influence exoplanet dynamics and formation.
This study analyzed high-resolution spectra of 125 compact stellar systems (CSSs) in the giant elliptical galaxy NGC 5128 to measure their radial velocities and velocity dispersions. Combining these measurements with structural parameters from imaging, dynamical masses were derived for 112 CSSs, including 89 for the first time. Two distinct sequences were found in the dynamical mass-to-light ratio vs dynamical mass plane, which can be approximated by power laws. The shallower sequence corresponds to bright globular clusters, while the steeper relation appears to be populated by objects requiring significant dark matter such as central black holes or concentrated dark matter. This suggests different formation histories for these CSSs compared to classical globular clusters in NGC 5128 and
This document outlines an Earth science curriculum for grades 1-5. It includes 9 units of study for each grade level with performance expectations aligned to disciplinary core ideas and science practices. The units cover topics like Earth's place in the universe and solar system, plate tectonics, weather and climate, and natural resources. Appendices provide templates for proficiency scales and curriculum refinement.
The SPHERE view of three interacting twin disc systems in polarised lightSérgio Sacani
Dense stellar environments as hosts of ongoing star formation increase the probability of gravitational encounters among stellar
systems during the early stages of evolution. Stellar interaction may occur through non-recurring, hyperbolic or parabolic passages
(a so-called ‘fly-by’), through secular binary evolution, or through binary capture. In all three scenarios, the strong gravitational
perturbation is expected to manifest itself in the disc structures around the individual stars. Here, we present near-infrared
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individuals’ contribution. This can produce nulls of polarised intensity in an image, as potentially observed in AS 205.We discuss
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The Dynamical Consequences of a Super-Earth in the Solar SystemSérgio Sacani
Placing the architecture of the solar system within the broader context of planetary architectures is one of the
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demographics is the relative prevalence of super-Earth planets, for which the solar system lacks a suitable analog,
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2–4 au, between the orbits of Mars and Jupiter. We show that, although the system dynamics remain largely
unaffected when the additional planet is placed near 3 au, Mercury experiences substantial instability when the
additional planet lies in the range 3.1–4.0 au, and perturbations to the Martian orbit primarily result when the
additional planet lies in the range 2.0–2.7 au. We further show that, although Jupiter and Saturn experience
relatively small orbital perturbations, the angular momentum transferred to the ice giants can result in their ejection
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The spectacular outbursts of energy associated with supernovae (SNe) have long motivated research into their
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the atmospheric damage associated with the prompt arrival of ionizing photons within days or months of the initial
outburst, and the high-energy cosmic rays that arrive thousands of years after the explosion. In this study, we turn
the focus to persistent X-ray emission, arising in certain SNe that have interactions with a dense circumstellar
medium and observed months and/or years after the initial outburst. The sustained high X-ray luminosity leads to
large doses of ionizing radiation out to formidable distances. We assess the threat posed by these X-ray-luminous
SNe for Earth-like planetary atmospheres; our results are rooted in the X-ray SN observations from Chandra, Swift-
XRT, XMM-Newton, NuSTAR, and others. We find that this threat is particularly acute for SNe showing evidence
of strong circumstellar interaction, such as Type IIn explosions, which have significantly larger ranges of influence
than previously expected and lethal consequences up to ∼50 pc away. Furthermore, X-ray-bright SNe could pose a
substantial and distinct threat to terrestrial biospheres and tighten the Galactic habitable zone. We urge follow-up
X-ray observations of interacting SNe for months and years after the explosion to shed light on the physical nature
and full-time evolution of the emission and to clarify the danger that these events pose for life in our galaxy and
other star-forming regions.
We present the 2020 version of the Siena Galaxy Atlas (SGA-2020), a multiwavelength optical and infrared
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Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys Data Release 9 and infrared imaging in
four bands (spanning 3.4–22 μm) from the 6 year unWISE coadds; it is more than 95% complete for galaxies larger
than R(26) ≈ 25″ and r < 18 measured at the 26 mag arcsec−2 isophote in the r band. The atlas delivers precise
coordinates, multiwavelength mosaics, azimuthally averaged optical surface-brightness profiles, model images and
photometry, and additional ancillary metadata for the full sample. Coupled with existing and forthcoming optical
spectroscopy from the DESI, the SGA-2020 will facilitate new detailed studies of the star formation and mass
assembly histories of nearby galaxies; enable precise measurements of the local velocity field via the Tully–Fisher
and fundamental plane relations; serve as a reference sample of lasting legacy value for time-domain and
multimessenger astronomical events; and more.
A Search for Technosignatures Around 11,680 Stars with the Green Bank Telesco...Sérgio Sacani
We conducted a search for narrowband radio signals over four observing sessions in 2020–2023 with
the L-band receiver (1.15–1.73 GHz) of the 100 m diameter Green Bank Telescope. We pointed the
telescope in the directions of 62 TESS Objects of Interest, capturing radio emissions from a total of
∼11,860 stars and planetary systems in the ∼9 arcminute beam of the telescope. All detections were
either automatically rejected or visually inspected and confirmed to be of anthropogenic nature. In
this work, we also quantified the end-to-end efficiency of radio SETI pipelines with a signal injection
and recovery analysis. The UCLA SETI pipeline recovers 94.0% of the injected signals over the usable
frequency range of the receiver and 98.7% of the injections when regions of dense RFI are excluded. In
another pipeline that uses incoherent sums of 51 consecutive spectra, the recovery rate is ∼15 times
smaller at ∼6%. The pipeline efficiency affects SETI search volume calculations as well as calculations
of upper bounds on the number of transmitting civilizations. We developed an improved Drake Figure
of Merit for SETI search volume calculations that includes the pipeline efficiency and frequency drift
rate coverage. Based on our observations, we found that there is a high probability (94.0–98.7%) that
fewer than ∼0.014% of stars earlier than M8 within 100 pc host a transmitter that is detectable in
our search (EIRP > 1012 W). Finally, we showed that the UCLA SETI pipeline natively detects the
signals detected with AI techniques by Ma et al. (2023).
The Variable Detection of Atmospheric Escape around the Young, Hot Neptune AU...Sérgio Sacani
This document summarizes observations from the Hubble Space Telescope of the young hot Neptune exoplanet AU Mic b, which orbits the nearby M dwarf star AU Mic. The observations aimed to detect atmospheric escape of neutral hydrogen through absorption in the stellar Lyman-alpha emission line. Two visits were obtained, one in 2020 and one in 2021, corresponding to transits of the planet. A stellar flare was observed and removed from the first visit data. In the second visit, absorption was detected in the blue wing of the Lyman-alpha line 2.5 hours before the white light transit, indicating the presence of high-velocity neutral hydrogen escaping the planet's atmosphere and traveling toward the observer. Estimates place the column density of this material
The document provides an overview of the field of astrobiology, including its history and goals. It discusses the search for life on Mars, Europa and beyond Earth. The goals of astrobiology include understanding the origin and distribution of life, characterizing habitable environments in the solar system and beyond, and determining how life emerges and evolves in different environments. Both long term goals like searching for life on other worlds and short term goals like Mars exploration are mentioned.
Large-scale Volcanism and the Heat Death of Terrestrial WorldsSérgio Sacani
This document discusses the potential for large igneous provinces (LIPs) to cause the "heat death" of terrestrial planets through massive volcanic eruptions that overwhelm the climate system. It examines the timing of LIP events on Earth to estimate the likelihood of nearly simultaneous eruptions. Statistical analysis of Earth's LIP record finds that eruptions within 0.1-1 million years of each other are likely. Simultaneous LIPs could have driven Venus into a runaway greenhouse effect like its current state. The timing of LIP events on Earth provides insight into potential past LIP activity on Venus that may have ended its hypothesized earlier temperate climate.
This document describes a model of crater formation on the Moon and terrestrial planets based on the current understanding of the impactor population in the inner Solar System. The model calculates impact rates spatially across planetary surfaces to account for nonuniform cratering. It finds that the lunar cratering rate varies with latitude and longitude, being about 25% lower in some regions and higher in others. The model reconciles measured lunar crater size-frequency distributions with observations of near-Earth objects, assuming the presence of a porous lunar megaregolith affects the size of small craters. It provides revised estimates of the ages of some lunar and planetary geological features based on crater counts and the derived crater chronology.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
The vvv survey_reveals_classical_cepheids_tracing_a_young_and_thin_stellar_di...Sérgio Sacani
Com o auxílio do telescópio VISTA instalado no Observatório do Paranal do ESO, astrônomos descobriram uma componente anteriormente desconhecida da Via Láctea. Ao mapear a localização de uma classe de estrelas que variam em brilho chamadas Cefeidas, foi descoberto um disco de estrelas jovens enterradas por trás de espessas nuvens de poeira no bojo central.
O rastreio público do ESO VISTA Variables in the Vía Láctea (VVV) [1] usa o telescópio VISTA instalado no Observatório do Paranal para obter imagens múltiplas em épocas diferentes das regiões centrais da nossa Galáxia nos comprimentos de onda do infravermelho [2]. O rastreio está descobrindo uma enorme quantidade de novos objetos, incluindo estrelas variáveis, aglomerados e estrelas em explosão (eso1101, eso1128, eso1141).
Uma equipe de astrônomos, liderada por Istvan Dékány da Pontificia Universidad Católica de Chile, utilizou dados deste rastreio, obtidos entre 2010 e 2014, para fazer uma descoberta notável — um componente anteriormente desconhecido da Via Láctea, a Galáxia que nos acolhe.
Kinematics and simulations_of_the_stellar_stream_in_the_halo_of_the_umbrella_...Sérgio Sacani
This document summarizes a study of the stellar stream and substructures around the Umbrella Galaxy (NGC 4651). Deep imaging and spectroscopy were used to characterize the properties and kinematics of the stream. Tracer objects like globular clusters and planetary nebulae were identified and found to delineate a kinematically cold feature in position-velocity space. Dynamical modeling suggests the stream originated from the tidal disruption of a dwarf galaxy on a highly eccentric orbit about 6-10 billion years ago. This work demonstrates the feasibility of using discrete tracers to recover the kinematics and model the dynamics of low surface brightness stellar streams around distant galaxies.
Exploring the nature and synchronicity of early cluster formation in the Larg...Sérgio Sacani
We analyse Hubble Space Telescope observations of six globular clusters in the Large Magel- lanic Cloud (LMC) from programme GO-14164 in Cycle 23. These are the deepest available observations of the LMC globular cluster population; their uniformity facilitates a precise comparison with globular clusters in the Milky Way. Measuring the magnitude of the main- sequence turn-off point relative to template Galactic globular clusters allows the relative ages of the clusters to be determined with a mean precision of 8.4 per cent, and down to 6 per cent for individual objects. We find that the mean age of our LMC cluster ensemble is identical to the mean age of the oldest metal-poor clusters in the Milky Way halo to 0.2 ± 0.4 Gyr. This provides the most sensitive test to date of the synchronicity of the earliest epoch of globular cluster formation in two independent galaxies. Horizontal branch magnitudes and subdwarf fitting to the main sequence allow us to determine distance estimates for each cluster and examine their geometric distribution in the LMC. Using two different methods, we find an average distance to the LMC of 18.52 ± 0.05.
The document analyzes the merger fractions of radio-loud and radio-quiet active galactic nuclei (AGN) at z > 1 using new Hubble Space Telescope (HST) samples. It finds that 92% (+8%/-14%) of radio-loud galaxies at z > 1 show evidence of recent or ongoing mergers, while only 38% (+16%/-15%) of matched radio-quiet samples exhibit mergers. This provides strong evidence that mergers are the triggering mechanism for radio-loud AGN phenomena like relativistic jet launching, and that major black hole mergers may spin up central supermassive black holes in these objects.
The document discusses current research in the field of astrobiology. It covers research being done on Mars, Enceladus, and Titan to discover evidence of ancient or current life. On Mars, methane pulses detected by the Curiosity rover could potentially be produced by methanogens living underground. Enceladus shows signs of hydrothermal activity and a subsurface ocean, conditions that could support life. Titan, with its liquid hydrocarbon seas, may be able to support a hypothetical form of life called an azotosome, which could use nitrogen-based membranes instead of cell walls. The document argues that expanding our understanding of possible forms life could take is important for continuing progress in the search for life beyond Earth.
Similar to Beyond the Drake Equation: A Time-Dependent Inventory of Habitable Planets and Life-Bearing Worlds in the Solar Neighborhood (20)
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Sérgio Sacani
Mars is a particularly attractive candidate among known astronomical objects
to potentially host life. Results from space exploration missions have provided
insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to
its toxicity. However, it can also provide potential benefits, such as producing
brines by deliquescence, like those thought to exist on present-day Mars. Here
we show perchlorate brines support folding and catalysis of functional RNAs,
while inactivating representative protein enzymes. Additionally, we show
perchlorate and other oxychlorine species enable ribozyme functions,
including homeostasis-like regulatory behavior and ribozyme-catalyzed
chlorination of organic molecules. We suggest nucleic acids are uniquely wellsuited to hypersaline Martian environments. Furthermore, Martian near- or
subsurface oxychlorine brines, and brines found in potential lifeforms, could
provide a unique niche for biomolecular evolution.
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
WASP-69b’s Escaping Envelope Is Confined to a Tail Extending at Least 7 RpSérgio Sacani
Studying the escaping atmospheres of highly irradiated exoplanets is critical for understanding the physical
mechanisms that shape the demographics of close-in planets. A number of planetary outflows have been observed
as excess H/He absorption during/after transit. Such an outflow has been observed for WASP-69b by multiple
groups that disagree on the geometry and velocity structure of the outflow. Here, we report the detection of this
planet’s outflow using Keck/NIRSPEC for the first time. We observed the outflow 1.28 hr after egress until the
target set, demonstrating the outflow extends at least 5.8 × 105 km or 7.5 Rp This detection is significantly longer
than previous observations, which report an outflow extending ∼2.2 planet radii just 1 yr prior. The outflow is
blueshifted by −23 km s−1 in the planetary rest frame. We estimate a current mass-loss rate of 1 M⊕ Gyr−1
. Our
observations are most consistent with an outflow that is strongly sculpted by ram pressure from the stellar wind.
However, potential variability in the outflow could be due to time-varying interactions with the stellar wind or
differences in instrumental precision.
X-rays from a Central “Exhaust Vent” of the Galactic Center ChimneySérgio Sacani
Using deep archival observations from the Chandra X-ray Observatory, we present an analysis of
linear X-ray-emitting features located within the southern portion of the Galactic center chimney,
and oriented orthogonal to the Galactic plane, centered at coordinates l = 0.08◦
, b = −1.42◦
. The
surface brightness and hardness ratio patterns are suggestive of a cylindrical morphology which may
have been produced by a plasma outflow channel extending from the Galactic center. Our fits of the
feature’s spectra favor a complex two-component model consisting of thermal and recombining plasma
components, possibly a sign of shock compression or heating of the interstellar medium by outflowing
material. Assuming a recombining plasma scenario, we further estimate the cooling timescale of this
plasma to be on the order of a few hundred to thousands of years, leading us to speculate that a
sequence of accretion events onto the Galactic Black Hole may be a plausible quasi-continuous energy
source to sustain the observed morphology
What is greenhouse gasses and how many gasses are there to affect the Earth.moosaasad1975
What are greenhouse gasses how they affect the earth and its environment what is the future of the environment and earth how the weather and the climate effects.
The use of Nauplii and metanauplii artemia in aquaculture (brine shrimp).pptxMAGOTI ERNEST
Although Artemia has been known to man for centuries, its use as a food for the culture of larval organisms apparently began only in the 1930s, when several investigators found that it made an excellent food for newly hatched fish larvae (Litvinenko et al., 2023). As aquaculture developed in the 1960s and ‘70s, the use of Artemia also became more widespread, due both to its convenience and to its nutritional value for larval organisms (Arenas-Pardo et al., 2024). The fact that Artemia dormant cysts can be stored for long periods in cans, and then used as an off-the-shelf food requiring only 24 h of incubation makes them the most convenient, least labor-intensive, live food available for aquaculture (Sorgeloos & Roubach, 2021). The nutritional value of Artemia, especially for marine organisms, is not constant, but varies both geographically and temporally. During the last decade, however, both the causes of Artemia nutritional variability and methods to improve poorquality Artemia have been identified (Loufi et al., 2024).
Brine shrimp (Artemia spp.) are used in marine aquaculture worldwide. Annually, more than 2,000 metric tons of dry cysts are used for cultivation of fish, crustacean, and shellfish larva. Brine shrimp are important to aquaculture because newly hatched brine shrimp nauplii (larvae) provide a food source for many fish fry (Mozanzadeh et al., 2021). Culture and harvesting of brine shrimp eggs represents another aspect of the aquaculture industry. Nauplii and metanauplii of Artemia, commonly known as brine shrimp, play a crucial role in aquaculture due to their nutritional value and suitability as live feed for many aquatic species, particularly in larval stages (Sorgeloos & Roubach, 2021).
The ability to recreate computational results with minimal effort and actionable metrics provides a solid foundation for scientific research and software development. When people can replicate an analysis at the touch of a button using open-source software, open data, and methods to assess and compare proposals, it significantly eases verification of results, engagement with a diverse range of contributors, and progress. However, we have yet to fully achieve this; there are still many sociotechnical frictions.
Inspired by David Donoho's vision, this talk aims to revisit the three crucial pillars of frictionless reproducibility (data sharing, code sharing, and competitive challenges) with the perspective of deep software variability.
Our observation is that multiple layers — hardware, operating systems, third-party libraries, software versions, input data, compile-time options, and parameters — are subject to variability that exacerbates frictions but is also essential for achieving robust, generalizable results and fostering innovation. I will first review the literature, providing evidence of how the complex variability interactions across these layers affect qualitative and quantitative software properties, thereby complicating the reproduction and replication of scientific studies in various fields.
I will then present some software engineering and AI techniques that can support the strategic exploration of variability spaces. These include the use of abstractions and models (e.g., feature models), sampling strategies (e.g., uniform, random), cost-effective measurements (e.g., incremental build of software configurations), and dimensionality reduction methods (e.g., transfer learning, feature selection, software debloating).
I will finally argue that deep variability is both the problem and solution of frictionless reproducibility, calling the software science community to develop new methods and tools to manage variability and foster reproducibility in software systems.
Exposé invité Journées Nationales du GDR GPL 2024
hematic appreciation test is a psychological assessment tool used to measure an individual's appreciation and understanding of specific themes or topics. This test helps to evaluate an individual's ability to connect different ideas and concepts within a given theme, as well as their overall comprehension and interpretation skills. The results of the test can provide valuable insights into an individual's cognitive abilities, creativity, and critical thinking skills
When I was asked to give a companion lecture in support of ‘The Philosophy of Science’ (https://shorturl.at/4pUXz) I decided not to walk through the detail of the many methodologies in order of use. Instead, I chose to employ a long standing, and ongoing, scientific development as an exemplar. And so, I chose the ever evolving story of Thermodynamics as a scientific investigation at its best.
Conducted over a period of >200 years, Thermodynamics R&D, and application, benefitted from the highest levels of professionalism, collaboration, and technical thoroughness. New layers of application, methodology, and practice were made possible by the progressive advance of technology. In turn, this has seen measurement and modelling accuracy continually improved at a micro and macro level.
Perhaps most importantly, Thermodynamics rapidly became a primary tool in the advance of applied science/engineering/technology, spanning micro-tech, to aerospace and cosmology. I can think of no better a story to illustrate the breadth of scientific methodologies and applications at their best.
Current Ms word generated power point presentation covers major details about the micronuclei test. It's significance and assays to conduct it. It is used to detect the micronuclei formation inside the cells of nearly every multicellular organism. It's formation takes place during chromosomal sepration at metaphase.
Travis Hills' Endeavors in Minnesota: Fostering Environmental and Economic Pr...Travis Hills MN
Travis Hills of Minnesota developed a method to convert waste into high-value dry fertilizer, significantly enriching soil quality. By providing farmers with a valuable resource derived from waste, Travis Hills helps enhance farm profitability while promoting environmental stewardship. Travis Hills' sustainable practices lead to cost savings and increased revenue for farmers by improving resource efficiency and reducing waste.
Phenomics assisted breeding in crop improvementIshaGoswami9
As the population is increasing and will reach about 9 billion upto 2050. Also due to climate change, it is difficult to meet the food requirement of such a large population. Facing the challenges presented by resource shortages, climate
change, and increasing global population, crop yield and quality need to be improved in a sustainable way over the coming decades. Genetic improvement by breeding is the best way to increase crop productivity. With the rapid progression of functional
genomics, an increasing number of crop genomes have been sequenced and dozens of genes influencing key agronomic traits have been identified. However, current genome sequence information has not been adequately exploited for understanding
the complex characteristics of multiple gene, owing to a lack of crop phenotypic data. Efficient, automatic, and accurate technologies and platforms that can capture phenotypic data that can
be linked to genomics information for crop improvement at all growth stages have become as important as genotyping. Thus,
high-throughput phenotyping has become the major bottleneck restricting crop breeding. Plant phenomics has been defined as the high-throughput, accurate acquisition and analysis of multi-dimensional phenotypes
during crop growing stages at the organism level, including the cell, tissue, organ, individual plant, plot, and field levels. With the rapid development of novel sensors, imaging technology,
and analysis methods, numerous infrastructure platforms have been developed for phenotyping.
ESPP presentation to EU Waste Water Network, 4th June 2024 “EU policies driving nutrient removal and recycling
and the revised UWWTD (Urban Waste Water Treatment Directive)”
Beyond the Drake Equation: A Time-Dependent Inventory of Habitable Planets and Life-Bearing Worlds in the Solar Neighborhood
1. Draft version September 22, 2023
Typeset using L
A
TEX twocolumn style in AASTeX631
Beyond the Drake Equation: A Time-Dependent Inventory of Habitable Planets and Life-Bearing
Worlds in the Solar Neighborhood
Piero Madau1
1Department of Astronomy & Astrophysics, University of California, 1156 High Street, Santa Cruz, CA 95064
ABSTRACT
We introduce a mathematical framework for statistical exoplanet population and astrobiology studies
that may help directing future observational efforts and experiments. The approach is based on a
set of differential equations and provides a time-dependent mapping between star formation, metal
enrichment, and the occurrence of exoplanets and potentially life-harboring worlds over the chemo-
population history of the solar neighborhood. Our results are summarized as follows: 1) the formation
of exoplanets in the solar vicinity was episodic, starting with the emergence of the thick disk about
11 Gyr ago; 2) within 100 pc from the Sun, there are as many as 11, 000 (η⊕/0.24) Earth-size planets
in the habitable zone (“temperate terrestrial planets” or TTPs) of K-type stars. The solar system is
younger than the median TTP, and was created in a star formation surge that peaked 5.5 Gyr ago and
was triggered by an external agent; 3) the metallicity modulation of the giant planet occurrence rate
results in a later typical formation time, with TTPs outnumbering giant planets at early times; 4) the
closest, life-harboring Earth-like planet would be ∼
< 20 pc away if microbial life arose as soon as it did
on Earth in ∼
> 1% of the TTPs around K stars. If simple life is abundant (fast abiogenesis), it is also
old, as it would have emerged more than 8 Gyr ago in about one third of all life-bearing planets today.
Older Earth analogs are more likely to have developed sufficiently complex life capable of altering the
environment and producing detectable oxygenic biosignatures.
Keywords: Astrobiology – Exoplanets – Habitable Planets – Metallicity – Solar Neighborhood – Star
Formation
1. INTRODUCTION
The search for habitable exoplanets and extraterres-
trial life beyond the solar system is a topic of cen-
tral interest for modern science, and one of the most
compelling and consequential endeavors for humankind.
Simple life emerged on Earth within the first billion
year of its habitable window, and the high frequency
of terrestrial planets in the habitable zones around GK
dwarf stars inferred from NASA’s Kepler observations
(Bryson et al. 2021) invites the question of how often (if
at all) life may have arisen on other worlds in the past.
This pursuit will ultimately require statistical analyses
of the population of habitable systems, in-depth stud-
ies of the climates of individual planets, and searches
for chemical biomarkers (Schwieterman et al. 2018), and
has motivated the development of the next generation of
large ground-based facilities and instrumentation. The
yield and characterization of Earth-like planets will be
a primary science metric for future space-based flagship
missions, but the optimal observational strategy for ad-
dressing the origin and properties of planetary systems
and the prevalence of habitable exoplanets and life be-
yond the solar system remains unclear (e.g., Batalha
et al. 2023; Sarkar 2022; Sandora & Silk 2020; Checlair
et al. 2021; Truitt et al. 2020; Bean et al. 2017; Tasker
et al. 2017). The gathering of comprehensive data for
each individual system is impractical if not impossi-
ble, so a statistical perspective is necessary to prioritize
targets for follow up observations. In particular, one
would like to identify – given a model of habitability
and biosignature genesis – how potential biosignature
yields change during the evolution of a stellar system
as a function of stellar properties like age, mass, and
metallicity.
This paper aims to present a theoretical framework
for exoplanet population and astrobiology studies that
may provide a better statistical understanding of the
formation history, frequency, age and metallicity distri-
butions of different planet types around stars of different
properties. Our approach may also establish a useful ba-
sis for testing hypotheses about habitable environments
arXiv:2309.11927v1
[astro-ph.EP]
21
Sep
2023
2. 2 Beyond the Drake Equation
and life beyond the solar system, for gaining a sense of
biosignature yields, and for informing future observa-
tional efforts and experiments. A well-known parame-
terization of the present-day abundance of life-bearing
worlds in the Galaxy, Nℓ, is represented by the first four
terms in the probabilistic Drake equation (Drake 1965),
which can be rewritten as
Nℓ = NMS(t0) fp ne fℓ. (1)
Here, NMS(t0) is the total number of stars that are on
the main sequence today and can provide their planets
a stable habitable zone, fp is the fraction of these stars
that have planetary systems, ne is the average number
per planetary system of Earth-size planets that are in
the habitable zone (HZ), and fℓ is the subset of these
rocky exoplanets that are “Earth-like” in a more detailed
biochemical and geophysical sense and where simple life
eventually arises. The first three terms (NMS, fp, ne) in
Equation (1) have already experimental measurements,
and the fourth (fℓ) is a conditional probability that
may potentially be observable in the coming decades
via spectroscopic searches for biosignature gases in ex-
oplanet atmospheres (Schwieterman et al. 2018; Seager
2018). In Drake’s famous formulation, in order to esti-
mate the number of active, communicative extraterres-
trial civilizations around us today, the right-hand side
of Equation (1) gets multiplied by the fraction fi of life-
bearing planets on which intelligent life emerges, times
the percentage fc of such civilizations that produces a
detectable signal, times the fractional longevity fL of a
technological species.
The Drake equation and its ‘Biosignature’ version
(Seager 2018) amount to a pedagogical and organiza-
tional summary of the factors that may affect the likeli-
hood of detecting technologically advanced civilizations
or just simple microbial life evolving on a habitable
planet. They are only meant to guide the observa-
tional inputs needed to make an educated guess, rather
than provide a time-dependent mapping between star
formation, environment, exoplanets, and life-harboring
worlds. Their inherent limitations include both the lack
of temporal structure (e.g., Kipping 2021; Cai et al.
2021; Forgan 2009; Ćirković 2004) – an assumption of
uniformity with time that precludes the inclusion of evo-
lutionary effects associated with, e.g., the star formation
and chemical enrichment history of the local Galactic
disk and the timeline of life emergence – as well as the
difficulty of casting in a probabilistic argument the vari-
ety of phenomena and associated timescales that may
influence anything quantified by probability f-factors
and multiplicity ne. Recent rapid developments in as-
trophysics and planetary sciences warrant a more in-
formative and modern evolutionary framework, a rate-
equation approach based on a system of first order dif-
ferential equations. These describe the changing rates
of star, metal, planet, and habitable world formation
over the history of a given stellar system, and can easily
be adapted to incorporate the hierarchy of astrophysical
and biological processes that regulate the age-dependent
inventory of any key planet population.
The field of Galactic habitability and the formation
history of Earth-like and giant planets in the Milky
Way and the Universe as a whole have been a research
topic for more than two decades (e.g., Gonzalez et al.
2001; Lineweaver et al. 2004; Gowanlock et al. 2011;
Behroozi & Peeples 2015; Zackrisson et al. 2016; Go-
bat & Hong 2016; Forgan et al. 2017; Balbi et al. 2020).
Our approach expands upon some of the ideas employed
in these early papers and develops new ones, focus-
ing instead on the time-varying incidence of exoplan-
ets and potentially habitable worlds over the chemo-
population history of the solar neighborhood, the target
of current and next-generation stellar and planetary sur-
veys. This is the locale where more detailed calculations
are justified by an avalanche of new data and actually
needed in order to estimate, given a model of habitabil-
ity and biosignature genesis, the relative biosignature
yields among potential target stars.
The plan of this paper is as follows. In Section 2 we
present the basic rationale and main ingredients of our
modeling: the star formation history (SFH) and metal-
licity distribution function (MDF) in the solar vicinity,
the planet occurrence rate around GK stars, and vari-
ous metallicity-dependent effects. In Section 3 we cast
and integrate our rate equations for the time evolution
of the local abundance of dwarf stars and the giant plan-
ets and rocky planets in the HZ around them. We track
giant planets to gauge the impact of their enhanced oc-
currence rate at higher host star metallicities relative to
the weaker frequency-metallicity correlation of terres-
trial planets. In Section 4 we extend our formalism to
speculate about the formation history of life-harboring
environments in the local volume under the hypothesis
of a rapid abiogenesis process on Earth-like planets, and
estimate the prevalence of nearby biospheres in terms of
the exoplanet census as a whole. Finally, we summarize
our findings and conclusions in Section 5.
2. BASIC STELLAR AND PLANETARY
ASTROPHYSICS
In order to provide absolute number counts in the so-
lar vicinity we shall use the recent tally of main-sequence
stars, giants, and white dwarfs within 100 pc of the Sun
from the Gaia Early Data Release 3 (EDR3). The Gaia
3. Madau 3
catalog of Nearby Stars contains
N⋆(t0) = 331, 312 (2)
objects and is estimated to be > 92% complete down to
faint stellar type M9 (Gaia Collaboration et al. 2021).
Apart for a minor correction (a fraction of a percent for
the initial mass function in Eq. 4) associated with the
contribution of remnant neutron stars and black holes,
N⋆(t0) represents the total number of stars ever formed
in the Solar neighborhood. Below, we shall use this nor-
malization together with a star formation history and
an initial mass function to compute the number of main
sequence stars as a function of time.
2.1. Star Formation History
Let ϕ(m) and ψ(t) be the (universal) initial mass func-
tion (IMF) and star formation history (SFH) by num-
ber, respectively. The IMF and SFH are normalized so
that
R t0
0
ψ(t)dt = 1 =
R mu
ml
ϕ(m)dm. The number of
stars that are on the main sequence at time t, NMS(t),
evolves at the rate
ṄMS(t) = N⋆(t0)
Z
ϕ(m)[ψ(t) − ψ(t − tMS)]dm, (3)
where the dot denotes the time derivative, tMS(m) < t
is the main-sequence lifetime, and the second term in
the square brackets corrects the rate of newly formed
main-sequence stars for the number of stars that have
evolved off the main sequence. In the following, we shall
assume a Kroupa (2001) IMF,
ϕ(m) =
0.2530 m−1.3
(0.08 ≤ m < 0.5)
0.1265 m−2.3
(0.5 ≤ m < 100),
(4)
where m is measured in solar masses. The main-
sequence lifetime tMS can be computed using the an-
alytical fitting formulae of Hurley et al. (2000) (based
on the evolutionary tracks of Pols et al. 1998) as a func-
tion of m and metallicity Z (see Fig. 1).1
A G-type
m = 1 main-sequence star, for example, has a lifetime
of tMS = 11 Gyr at solar metallicity, and tMS = 6.5 Gyr
at Z = 0.1 Z⊙.
The SFH of the solar neighborhood has been recently
reconstructed by Alzate et al. (2021) using all 120,452
stars brighter than G = 15 mag within 100 pc of the the
1 Other stellar evolution models could be adopted (Valle et al.
2014; Truitt et al. 2015; Stancliffe et al. 2016), but the resulting
changes would not be significant in this context, as uncertainties
in the input physics and solar composition lead to errors that are
small compared to those associated with, e.g., uncertainties in
the local SFH and exoplanet occurrence rates.
Figure 1. Main-sequence lifetimes tms for stars with masses
of 0.7, 0.8, 0.9, and 1.0 M⊙ (from top to bottom) at different
metallicities, −2.2 < log10(Z/Z⊙) < 0.4 (Hurley et al. 2000,
“old” solar composition). The points show the results of
the more recent stellar evolution calculations by Truitt et al.
(2015) (“enhanced oxygen abundance” model).
Sun in the Gaia DR2 catalog. In broad agreement with
previous determinations based on different techniques
and data sets (e.g., Ruiz-Lara et al. 2020; Mor et al.
2019; Snaith et al. 2015), their results show two main
early episodes of star formation: 1) a peak of activity oc-
curing 10 Gyr ago that produced a significant number of
stars with sub-solar metallicities, followed by a star for-
mation minimum (quenching) around 8 Gyr ago; and 2)
a more recent burst about 5.5 Gyr ago. Since then, star
formation has been declining until recent times, making
stars with super-solar metallicities in short-lived bursts
of activity.
Most low-metallicity 10 Gyr-old stars belong to the
thick Galactic disk population (e.g. Haywood et al. 2019;
Robin et al. 2014), as opposed to the thin disk for the
rest of them. Clear evidence of a thick disk peak at age
9.8 ± 0.3 Gyr is also seen in the local white dwarf lumi-
nosity function by Fantin et al. (2019). An intense phase
of star formation between 9 and 13 Gyr ago during the
emergence of the thick disc, producing about as much
mass in stars as that manufactured in the next 8 Gyr,
and followed by a minimum in the star formation rate
at an age of ∼ 8 Gyr, was also apparent in the SFH re-
construction of Snaith et al. (2015, 2014). In the 2-kpc
bubble around the Sun, Ruiz-Lara et al. (2020) inferred
three recent episodes of enhanced star formation dated
∼ 5.7, 1.9 and 1 Gyr, in synchrony with the estimated
Sagittarius dwarf galaxy pericentre passages.
Figure 2 shows the marginalized posterior SFH of so-
lar neighborhood stars from Alzate et al. (2021) together
with a reasonable reconstruction involving four Gaus-
sians centered at ages of 10, 5.5, 2.0 and 0.7 Gyr, and
4. 4 Beyond the Drake Equation
Figure 2. The star formation history of the solar neigh-
borhood. The blue pentagons with error bars show the
marginalized age distirbution (the fraction of stars formed
per unit time at age t0 − t) inferred by Alzate et al. (2021)
(grid C, extinction corrected) for stars brighter than G = 15
mag in Gaia DR2. The solid curve displays a reasonable re-
construction of the local SFH involving four Gaussians cen-
tered at ages of 10, 5.5, 2.0 and 0.7 Gyr, having widths of
1.2, 0.9, 0.35, and 0.3 Gyr, respectively, and relative peaks
1:1.36:0.71:0.86. The dotted line indicates the three late
peaks in the SFH (with a different normalization for illus-
tration purposes) of the (kinematically defined) thin stellar
disk derived by Ruiz-Lara et al. (2020).
having widths of 1.2, 0.9, 0.35, and 0.3 Gyr, respectively.
In this reconstruction, which we use in the rest of this
paper, about one third of all stars belong to the old > 9
Gyr population, and only 17% to the youngest, < 3 Gyr
component. There are periods of very little star forma-
tion around 7 − 8 Gyr ago and then again 3 Gyr ago.
Note that, although the analysis by Alzate et al. (2021)
uses a local sample, radial migration predicts that stars
in the close solar vicinity may represent a mixture of
stars born at various Galactocentric distances over the
disk (see, e.g., Lian et al. 2022, and references therein).
2.2. Metallicity PDF and Age-Metallicity Relation
To study the influence of stellar metallicity on the oc-
currence rates of planets and planetary systems, we shall
adopt here the metallicity distribution function (MDF)
from the GALAH+TGAS spectroscopic survey of dwarf
stars in the solar galactic zone (Buder et al. 2019). Fig-
ure 3 shows the data histogram and the correspond-
ing best-fit skewed distribution, G(M), with moments
⟨M⟩ = −0.07, σM = 0.23, and Skew = −0.51, that ac-
counts for the asymmetry of the extended metal-poor
tail as well as the sharper truncation of the MDF on the
metal-rich side. Here and below, we use the symbol M
interchangeably with log10(Z/Z⊙) for compactness, and
Figure 3. Metallicity distribution function of the
GALAH+TGAS sample (red histogram, Buder et al. 2019).
The distribution is skewed towards the metal-poor tail, with
59% of the stars having metallicities below solar. Note
that, for plotting purposes, the histogram is expressed in
densities and not in frequencies. The blue line shows a
best-fit distribution in bins of M of the form G(M) =
a(10M
)b
exp(−c10M
), where M ≡ log10 Z/Z⊙, a = 128,
b = 4.1, and c = 4.25. The mean metallicity, standard de-
viation, and skewness of the distribution are provided in the
text.
the metallicity distribution g(Z) is related to the MDF
in bins of M as g(Z) = G(M)/(10M
ln 10).
Solar neighborhood stars exhibit an age–metallicity
relation, such that young age correlates with high metal-
licity, a temporal sequence that is the fossil record of the
enrichment history of the Galactic disc (e.g., Haywood
et al. 2019; Hayden et al. 2015; Haywood et al. 2013).
Observations have shown that this relation has a signifi-
cant scatter, attributed to the effects of radial migration
and chemical mixing. Since our aim here is to correctly
characterize only the prevalent metallicity in each star
formation episode, we shall impose an age-metallicity
relationship ignoring the dispersion around the mean –
this is found to increase steadily with stellar age from
0.17 dex at age 2 Gyr to 0.35 dex at 13 Gyr (Buder et al.
2019). Within this framework, the fraction of stars that
formed between time t and t + dt, ψ(t)dt, is then equal
to the fraction of stars with metallicity between Z(t)
and Z(t) + dZ, g(Z)dZ. The typical stellar metallicity
therefore evolves with time as
Ż(t) = ψ(t)/g(Z). (5)
The derived age-metallicity relation Z(t) is depicted in
Figure 4. In broad agreement with previous results, it
exhibits a rapid increase in metallicity at early epochs
with an enrichment timescale of about 4 Gyr, followed
5. Madau 5
by a slow evolution around solar values at ages between
4 and 10 Gyr and an upward trend towards super-solar
metallicities at more recent times (e.g., Sharma et al.
2021; Snaith et al. 2015; Haywood et al. 2013).
Figure 4. Stellar age-metallicity relation in the solar neigh-
borhood. The solid curve shows the result of the integration
of Eq. (5) for the assumed SFH ψ(t) (Fig. 2), and MDF
g(Z) (Fig. 3). The inferred relationship is in broad agree-
ment with the mean abundance trends versus age recovered
by Snaith et al. (2015) for the inner (dashed curve) and outer
(dot-dashed curve) Milky Way disk. Note that stars in the
solar vicinity have none of the characteristics of inner disk
stars, and are better described as outer disk objects (Hay-
wood et al. 2019).
We note in passing that the age-metallicity distribu-
tion may actually consist of two distinct populations, an
old and a younger sequence corresponding to the forma-
tion of respectively the thick and the thin disk (Nissen
et al. 2020). An analysis of the implications of this sce-
nario is postponed to future work.
2.3. Planet Occurrence Frequency Around FGK Stars
Exoplanet statistics in the inner regions of FGK dwarf
stars has been investigated using the large and homoge-
neous sample from the Kepler mission (Thompson et al.
2018). Kepler planets commonly reside in multi-planet
systems, and the integrated occurrence rate (the av-
erage number of planets per star) for exoplanets with
radii in the range 1 − 20 R⊕ and orbital periods up to
P = 400 days is (Zhu & Dong 2021)
ηP = 1.23 ± 0.06. (6)
Earth-size exoplanets in Earth-like orbits are not well
probed by Kepler, and estimates of their frequencies
are more uncertain. A recent analysis by Bryson et al.
(2020) (see also Burke et al. 2015) yields
η1 = 0.015+0.011
−0.0007 (7)
for the occurrence rate around GK dwarf stars of terres-
trial planets within 20% of Earth’s orbital period and
radius.
The planet radius-orbital period parameter space
defining η1 is a subset of the larger parameter space
for η⊕, the occurrence rate of Earth-size rocky planets
in the HZ (hereafter “temperate terrestrial planets” or
TTPs for short), roughly defined as the region around
a Sun-like star in which a rocky planet with an Earth-
like atmospheric composition can sustain liquid water
on its surface (Kasting et al. 1993). The basic require-
ment for surface liquid water is predicated on a subset of
the minimum conditions needed for a simple, microbial
biosphere. Defining η⊕ as the occurrence rate of TTPs
with radii between 0.5 and 1.5 R⊕ and orbiting stars
with effective temperatures between 4,800 and 6,300 K,
Bryson et al. (2021) recently derived
0.37+0.48
−0.21 < η⊕ < 0.60+0.90
−0.36, (8)
where the errors reflect 68% confidence intervals and the
lower and upper bounds correspond to different com-
pleteness corrections. This occurrence rate uses the con-
servative HZ estimates from Kopparapu et al. (2014).
Below, we shall adopt a fiducial present-day occur-
rence rate of η⊕ = 0.24. This is the standard value
used in forecasting TTP yields from direct-imaging fu-
ture flagship missions like HabEx and LUVOIR, and is
based on the NASA ExoPAG SAG13 meta-analysis of
Kepler data (Kopparapu et al. 2018). Note that, in the
language of Drake’s Equation (1), η⊕ ≡ fpne.
For comparison, the frequency of giant gaseous planets
with radii > 4 R⊕ and orbital periods P < 400 days is
estimated by Zhu & Dong (2021) to be
ηGP = 0.16 ± 0.015. (9)
2.4. Dependence of Planet Frequency on Stellar
Metallicity
In the context of core-accretion planet formation the-
ory, metal-rich proto-planetary disks have enhanced sur-
face densities of solids, leading to the more-efficient for-
mation of the rocky cores of gas giant planets (Ida & Lin
2004; Pollack et al. 1996). Is is well established obser-
vationally that metal-rich stars are more likely to host
close-in giant planets (e.g., Zhu 2019; Petigura et al.
2018; Fischer & Valenti 2005), with an occurrence rate
enhancement as a function of metallicity of the form
f(Z) = A(Z/Z⊙)2
. (10)
For a sample of stars with metallicity distribution g(Z),
the normalization constant A above is related to the
integrated frequency of giant planets by (Zhu et al. 2016)
6. 6 Beyond the Drake Equation
ηGP =
Z
g(Z)f(Z)dZ. (11)
With the adopted MDF (Fig. 3), one derives A =
0.1369.
Small planets show a weaker frequency-metallicity
correlation (Petigura et al. 2018; Buchhave et al. 2012;
Sousa et al. 2008). Most recently, Lu et al. (2020)
were unable to confirm or reject a relationship between
planet occurrence and host star metallicity for rocky
planets with radii ∼
< 2R⊕. In line with these analy-
ses, no frequency-metallicity correlation for terrestrial
planets will be assumed in our treatment. We shall also
ignore possible correlations between small planet occur-
rence rates and α-element enhancement (Bashi et al.
2020).
2.5. Critical Metallicity for Terrestrial Planet
Formation
In the core accretion model of planet formation heavy
elements are necessary to form the dust grains and plan-
etesimals that build planetary cores. Johnson & Li
(2012) estimated a minimum metallicity Zc for planet
formation by comparing the timescale for dust grain
growth and settling to that for proto-planetary disk
photoevaporation. They found that, for an Earth-size
planet to form, a disk of surface density Σ(r) must have
a metallicity
Z ∼
> 0.1 Z⊙
Σ(1 AU)
103 g cm−2
−0.48
. (12)
Given the observed MDF (Fig. 3), the existence of a
fiducial metallicity floor Zc = 0.1 Z⊙ for the formation of
terrestrial planets will only impact a small fraction of the
census population in the solar neighborhood. Neverthe-
less, in our equations below we shall formally multiply
the integrated occurrence rate of TTPs by the Heaviside
function θ(Z–Zc).
2.6. Effect of Metallicity on the Habitable Zone
Low-metallicity stars have higher luminosities LZAMS
and higher effective temperatures Teff than metal-rich
stars of the same mass (e.g., Tout et al. 1996). An m = 1
zero-age main-sequence (ZAMS) star of metallicity Z =
0.1 Z⊙, for example, is 80% brighter, 13% hotter, and
has a larger HZ than its solar metallicity counterpart.
Conversely, an F-type star with m = 1.5 and Z = 0.1 Z⊙
has a main-sequence lifetime of only 1.8 Gyr (vs. 2.7
Gyr at solar metallicity), and is unlikely to be a good
candidate for harboring continuously habitable planets.
We assess the impact of stellar metallicity on the hab-
itability of terrestrial exoplanets around GK stars (see
Figure 5. ZAMS habitable zone limits for a 1 M⊕ planet
around m = 1 G-type host stars of different metallici-
ties. The inner HZ (blue curve) is defined by the run-
away greenhouse limit, while the red curve marks the
outer HZ – the maximum greenhouse limit. Stellar effec-
tive temperatures and luminosities were computed follow-
ing Tout et al. (1996), and the y-axis covers the range
from (LZAMS/L⊙, Teff ) = (0.70, 5635 K) at Z = 1.6 Z⊙ to
(LZAMS/L⊙, Teff ) = (1.34, 6464 K) at Z = 0.1 Z⊙. The effec-
tive incident fluxes determining the inner and outer HZ were
estimated using the parametric formulae of Kopparapu et al.
(2014).
also Truitt et al. 2015; Valle et al. 2014; Danchi Lopez
2013) adopting the conservative HZ estimates of Kop-
parapu et al. (2014), where the inner and outer edges
of the continuously HZ are defined by the “runaway
greenhouse” (atmosphere becomes opaque to outgoing
thermal radiation owing to excess amounts of H2O) and
“maximum greenhouse” (increased reflectivity of a thick
CO2 atmosphere wins out over greenhouse effect) limits.
The 1D, radiative–convective, cloud-free climate models
of Kopparapu et al. (2013) provide critical values for the
effective flux Seff – the normalized value of solar constant
required to maintain a given surface temperature – as a
function of the effective temperature of the host star,
Seff = Seff,⊙ + aT⋆ + bT2
⋆ + cT3
⋆ + dT4
⋆ , (13)
where T⋆ = Teff − 5760 K and the coefficients (a, b, c, d)
for the runaway greenhouse and maximum greenhouse
limits are listed in Kopparapu et al. (2014). Stellar effec-
tive temperatures and luminosities on the ZAMS were
computed as a function of metallicity following Tout
et al. (1996). The corresponding HZ distances can be
calculated using the relation
dZAMS =
LZAMS/L⊙
Seff
0.5
AU, (14)
7. Madau 7
where LZAMS/L⊙ is the luminosity of the star in solar
units.2
Figure 5 depicts the predicted variations in HZ
boundaries as a function of stellar metallicity for an m =
1 star. The effective stellar fluxes at the inner and outer
edge of the HZ increase at low Z’s because the calculated
planetary albedos become higher as the star’s radiation
is shifted toward the blue, a dependence that is stronger
at the outer HZ boundary because of the importance of
Rayleigh scattering in dense CO2 atmospheres (Kasting
et al. 2014). Note, e.g., how a 1 M⊕ planet at 1 AU from
an m = 1 ZAMS G-class dwarf of metallicity 0.1 Z⊙ is
just outside the inner edge of its host’s HZ, as this is
evaluated at 1.05 − 1.83 AU.
Figure 5 shows how, at low metallicities, the HZ moves
further away from the host star and is about 25% wider.
These differences in HZ boundaries may be relevant for
present and upcoming planet-finding surveys around low
metallicity stars (Dedrick et al. 2020). Because old age
correlates with low stellar metallicity, one might expect
η⊕ to be larger at earlier times if other factors, like the
efficiency of planetary formation and planetary spacing,
were equal. Given the relatively flat period distribution,
df/d ln p ∝ p0.2
, observed for long-period Kepler planets
(e.g., Bryson et al. 2020), however, the impact of such a
shift in HZ boundaries on the predicted occurrence rates
of TTPs around GK dwarfs in the young Galaxy should
be rather minor.
2.7. Habitable Zone Lifetime
The boundaries of a radiative HZ are not temporally
or spatially static but “migrate” outward over the course
of a star main sequence phase. The secular increase in
stellar luminosity results in a runaway greenhouse event,
which, in the case of Earth, will cause the cessation of
habitable condition and the likely extinction of our bio-
sphere about 1.5-2 Gyr in the future (e.g., De Sousa
Mello Santos Friaça 2020; Goldblatt Watson 2012),
well before the Sun becomes a red giant. The transitory
nature of the residence of a TTP within the HZ has
strong astrobiological implications and can be described
by the time a planet, located at a given distance from
a star, spends within the HZ (Waltham 2017; Danchi
Lopez 2013; Rushby et al. 2013). Here, we have used
the formulae and best-fitting coefficients of Hurley et al.
(2000) for the time-dependent luminosities and radii of
stars on the main-sequence to derive estimates for the
change in the HZ boundaries over time.
Figure 6 (top panel) shows the evolution of the inner
edge of the HZ, computed as before from the prescrip-
2 Throughout this paper, the ⊙ subscript denotes present-day val-
ues.
Figure 6. Time-dependent HZ boundaries around GK
dwarf stars. Top panel: Evolution of the inner boundary
of the HZ, di (in AU), from the ZAMS (corresponding to
τ = 0) to the end of the main sequence, as a function of
τ = t/tMS for stars of different mass and metallicities. Solid
lines: m = 0.7 (blue), m = 0.9 (orange), and m = 1.1
(green), all calculated at Z = 0.1 Z⊙. Dashed lines: same
for Z = Z⊙. The point on each curve denotes the time
when a hypothetical planet, formed in the center of the HZ
at the ZAMS stage, becomes uninhabitable. Bottom panel:
Habitable Zone lifetime tHZ (in Gyr) as a function of stellar
mass and metallicity. Solid blue line: Z = 0.1 Z⊙. Dashed
red line: Z = Z⊙. The dotted lines show the corresponding
main-sequence timescale.
tions of (Kopparapu et al. 2014), as a function of time
τ = t/tMS for GK dwarf stars of different mass and
metallicities. The point on each curve marks the char-
acteristic “HZ lifetime”, tHZ(m, Z), when a hypothetical
planet formed in the center of the HZ at the ZAMS stage
enters into the hot zone of the host star, undergoes a
runaway greenhouse event, and becomes uninhabitable
8. 8 Beyond the Drake Equation
(Rushby et al. 2013).3
Lower mass stars, while charac-
terized by longer main-sequence lifetimes, have propor-
tionally smaller tHZ/tMS ratios than higher-mass stars,
the result of their lower rates of stellar luminosity evolu-
tion (Rushby et al. 2013). At fixed mass, main-sequence
lifetimes are shorter and the total luminosity change over
the main-sequence is larger for lower metallicity stars
(Truitt et al. 2015). In the bottom panel of Figure 6
we compare the “HZ lifetime” with the main-sequence
timescale as a function of stellar mass and metallicity.
Over the plotted mass interval, the ratio tHZ/tMS ranges
from 0.75 to 0.90 at solar metallicities, and from 0.65 to
0.75 at 0.1 Z⊙. In absolute value terms, we find HZ life-
times that are longer than the age of the Galaxy for
m 0.9 (Z = Z⊙) and m 0.75 (Z = 0.1 Z⊙).
Below, we shall assume that the evolution of main-
sequence stars – rather than biogeochemical processes –
is the only factor controlling the collapse of the HZ zone
and the reduction of the biosphere lifespan. As the HZ
expands outward due to the effects of stellar evolution,
any planets that were initially beyond the boundaries of
the HZ – so-called “cold start” icy planets – could poten-
tially become habitable at later times as the HZ reaches
them. We shall neglect this possibility below as the de-
layed habitability of such globally-glaciated exoplanets
remains dubious (e.g., Yang et al. 2017).
3. EXOPLANETS AROUND K DWARFS
We can now cast our model for the time evolution of
the exoplanet population in the solar neighborhood into
a set of rate equations that can be then be integrated
as a function of time. Let us focus on K-class dwarfs
with masses between m1 = 0.45 and m2 = 0.80 and
main-sequence and HZ lifetimes that are typically longer
than the age of the Galaxy at the metallicities of interest
here. K stars may be better candidates in the search for
biosignatures than G dwarfs, as they are more abundant,
evolve less quickly on the main sequence, and provide
their planets a stable habitable zone (e.g., Tuchow
Wright 2020). They also offer a longer photochemical
lifetime of methane in the presence of oxygen compared
to G dwarfs and, being dimmer, provide a better planet-
star contrast ratio in direct imaging observations (Arney
3 Note that the habitable lifetime in fact changes with star-planet
separation, gradually increasing between the inner and outer
edges of the HZ, and that the full distribution of tHZ with dis-
tance should be taken into account in more advanced modelling
(e.g. Waltham 2017).
2019).4
For the assumed Kroupa IMF, the fraction of
stars that are classified as K-type is
F(m1, m2) ≡
Z 0.80
0.45
ϕ(m)dm = 0.14. (15)
Note that if the lower bound on habitability corre-
sponded to the spectral type K5 instead (m = 0.65 M⊙),
the factor F in Equation (15) would decrease by a fac-
tor of 3.5, while the inclusion of M dwarfs below 0.45
M⊙ would boost the same integral by a factor of 6. Of
course, for the occurrence rate of TTPs what matters is
the product η⊕ × F, so one could group some of the un-
certainties related to the lower habitability bound into
the factor η⊕.
3.1. Rate Equations
We can now track the evolution of the mean number
of K-type stars in the solar neighborhood, NK(t), and
the abundance of giant planets and TTPs around them,
NGP(t) and N⊕(t), by numerically integrating over time
the corresponding rates:
ṄK(t) = N⋆(t0)ψ(t)F,
ṄGP(t) = f[Z(t)]ṄK(t),
Ṅ⊕(t) = η⊕θ[Z(t) − Zc]ṄK(t).
(16)
Here, in the equation for Ṅ⊕(t), we have assumed that
exoplanets enter the HZ immediately after formation,
and interpreted the parameter η⊕ as the occurrence rate
of TTPs around K-class stars on the ZAMS. 5
The equa-
tions above must be supplemented by Equation (5) for
the evolution of the stellar metallicity Z(t).
Figure 7 shows the episodic formation history of ex-
oplanets that results from the integration of Equations
(16) for ηGP = 0.16 and η⊕ = 0.24. In our “solar vicin-
ity” sphere of 100 pc radius, there are currently about
4 The photochemical lifetime of methane in oxygenated atmo-
spheres is even longer around M dwarfs (Segura et al. 2005), but
M dwarf planet habitability may be hindered by extreme stel-
lar activity and a prolonged superluminous pre-main sequence
phase.
5 For more massive FG-type stars with main-sequence and HZ life-
times that are shorter than the age of the Galaxy, the rate equa-
tions (16) take the more complicated form:
ṄFG(t) = N⋆(t0)
Z
ϕ(m)[ψ(t) − ψ(t − tMS)]dm,
ṄGP(t) = f[Z(t)] ṄF G(t),
Ṅ⊕(t) = η⊕θ[Z(t) − Zc]ṄF G(t)
− η⊕θ[Z(t − t̄HZ) − Zc]ṄFG(t − t̄HZ).
(17)
The second term in the last equation approximately corrects the
rate of newly formed TTPs for the amount that has “migrated”
out of the HZ over the course of the star’s main sequence lifetime.
9. Madau 9
Figure 7. Exoplanet formation history in the solar neigh-
borhood. Top panel: K-class dwarf (solid curve), giant
planet (dashed curve), and TTP (dot-dashed curve) forma-
tion rates in a “solar vicinity” sphere of 100 pc radius, as a
function of age t0 − t. These estimates assume ηGP = 0.16
and η⊕ = 0.24 (see text for details). Bottom panel: Cumu-
lative number counts resulting from the integration of Eqs.
(16). Note how the solar system is younger than 77% of all
TTPs, and has an age that is comparable to that of the me-
dian giant planet.
11, 000 (η⊕/0.24) TTPs around K dwarfs. They have a
median age of 6.2 Gyr and 77% of them are older than
the solar system. The minimum metallicity threshold for
Earth-size planet formation of Johnson Li (2012) does
not significantly affect these numbers as the vast major-
ity of star formation has taken place at Z 0.1 Z⊙. By
contrast, the f(Z) modulation of the giant planet occur-
rence rate results in later typical formation times and
shifts their median age to 3.9 Gyr, with terrestrial plan-
ets vastly outnumbering giant planets at early times.
The early formation of TTPs in the solar vicinity oc-
curred largely in two major episodes of enhanced star
formation, starting with the emergence of the thick
disk about 11 Gyr ago and followed by a second event
that lasted 3.5 Gyr, peaked 5.5 Gyr ago, and involved
more than 40% of the total stellar counts today. The
five planet system Kepler-444, orbiting a metal-poor
11.2±1.0 Gyr old star, shows that thick-disk stars were
indeed the hosts of some of the oldest terrestrial planets
(Campante et al. 2015). The duration and size of the
second major star formation surge suggest an external
agent, perhaps a merger with a gas-rich satellite galaxy
(Mor et al. 2019) or the first passage of the Sagittarius
dwarf galaxy through the Milky Way’s disk (Ruiz-Lara
et al. 2020). Consistently with the Principle of Medi-
ocrity, the solar system formed near the peak of this
second episode. Over the last 4 Gyr the abundance of
TTPs around K stars has increased by +24%, while that
of giant planets has actually doubled.
4. SIMPLE LIFE IN THE SOLAR
NEIGHBORHOOD
In the coming decades, advanced space- and ground-
based observatories will allow an unprecedented oppor-
tunity to probe the atmospheres and surfaces of TTPs
in search for signs of life or habitability. The discov-
ery of extraterrestrial life would be a landmark mo-
ment in the history of science, with implications that
would reverberate throughout all of society. Much of
the early history of life on Earth has been dominated by
methanogenic microorganisms, and methane in anoxic,
Archean-like atmospheres is one of the most promising
exoplanet spectroscopic biosignatures (Thompson et al.
2022; Schwieterman et al. 2018). In spite of the re-
cent swift developments in astrophysics and planetary
sciences described in the previous sections, however,
the probability of abiogenesis on Earth-like planets is
currently unknown, as unknown are the characteristic
timescales over which biochemical complexity actually
evolves. The rapid emergence of life in the history of
Earth has been used to argue for a high abiogenesis rate
(e.g., Whitmire 2022; Kipping 2020; Lineweaver Davis
2002). A Bayesian framework may naturally account
for the anthropic bias that, if the timescale for intelli-
gence evolution is long, life’s early start may simply be
a prerequisite to our existence, rather than evidence for
simple primitive life being common on Earth-like worlds
(Spiegel Turner 2012). By means of this methodology,
the recent analysis by Kipping (2020) shows that a fast
abiogenesis scenario is at least 3 times more likely than
a slow one.
In preparation for the next generation of space- and
ground-based instruments, it seems interesting to con-
jecture on today’s prevalence and time-varying incidence
of microbial life-harboring worlds in the solar neighbor-
hood under the hypothesis of a rapid abiogenesis pro-
cess. We follow previous work (Kipping 2020; Chen
Kipping 2018; Scharf Cronin 2016; Spiegel Turner
10. 10 Beyond the Drake Equation
2012) and describe abiogenesis as a stochastic Poisson
process defined by a (uniform) rate parameter λℓ – the
mean number of abiogenesis events occurring per Earth-
like planet in a fixed time span, which we set equal to 1
Gyr. The probability of achieving at least one successful
abiogenesis event over a time interval t−t′
since a given
planet first became habitable at t′
is then given by
Pℓ(t − t′
) = 1 − e−λℓ (t−t′
)
. (18)
The time-dependent probability that life emerges on
a TTP can then be expressed as the product Pℓ(t −
t′
)P(ℓ|HZ), i.e. we distinguish here between the popu-
lation of planets that are “temperate” (i.e. Earth-size
rocky planets in the continuously HZ) and the subset
that are actually “habitable”, i.e. “Earth-like” in a more
detailed biochemical and geophysical sense, and where
simple life will eventually arise. The number of these
“Earth analogs” that formed (and became habitable)
between time t′
and t′
+ dt′
and where life emerged by
time t is dNℓ(t) = P(ℓ|HZ)Pℓ(t−t′
)Ṅ⊕(t′
)dt′
. Assuming
a probability P(ℓ|HZ) that is independent of time, we
can then write the mean number of life-hosting worlds
present at time t as the convolution integral
Nℓ(t) = P(ℓ|HZ)
Z t
0
Ṅ⊕(t′
)
h
1 − e−λℓ(t−t′
)
i
dt′
. (19)
Their formation rate must be given by the time deriva-
tive of Equation (19), yielding
Ṅℓ(t) = P(ℓ|HZ)
Z t
0
Ṅ⊕(t′
) λℓ e−λℓ(t−t′
)
dt′
. (20)
Note that, in the formalism of Drake’s Equation (1),
P(ℓ|HZ) = fℓ in the limit of fast abiogenesis.
The oldest, generally accepted evidence for life on
Earth comes from observations of microbial sulfate re-
duction in the 3.48 Gyr Dresser Formation (e.g., Lepot
2020). The Earth formed 4.54 ± 0.05 Gyr ago (Dalrym-
ple 2001), and mineralogical evidence from detrital zir-
cons indicates that liquid oceans must have been present
on Earth’s surface 4.404 ± 0.008 Gy ago (Wilde et al.
2001). The maximum plausible value for the time inter-
val over which at least one successful abiogenesis event
occurred on Earth is therefore ≃ 0.9−1 Gyr. This is con-
servatively long compared to the maximum-likelihood
timescale for life to first appear after conditions became
habitable, ∼ 190 Myr, inferred by Kipping (2020), and
much larger than the uncertainty as to when Earth be-
came suitable for life, justifying our approximation of
starting the “habitability clock” at formation.
Figure 8. Abiogenesis in the solar neighborhood. Long-
dashed green curve: Formation rate, Ṅℓ, of life-bearing ex-
oplanets as a function of age t0 − t. The calculation (Eq.
20) assumes a rapid abiogenesis process with rate parameter
λℓ = 1 Gyr−1
, and simple life eventually arising in all TTPs,
P(ℓ|HZ) = 1. Dot-dashed green curve: Cumulative number
counts of life-hosting exoplanets, Nℓ, resulting from the in-
tegration of Eq. (19). Blue curves: Same for life-hosting
planets undergoing a “Neoproterozoic Oxygenation Event”
(NOE) with rate parameter λ−1
O = 3.9 Gyr.
We have integrated Equations (19) and (20) above
assuming λℓ = 1 Gyr−1
, and plotted in Figure 8 the re-
sulting differential and cumulative number counts, Ṅℓ
and Nℓ. For illustration, we have assumed in the fig-
ure a conversion factor P(ℓ|HZ) = 1 between TTPs and
life-hosting Earths. Naturally, life would be abundant
(again, we are concerned here with the appearance of
the earliest life forms, not of intelligent life) in the so-
lar vicinity if abiogenesis was fast and early Earth-like
conditions existed and were relatively common on other
worlds for 1 Gy or more. The closest life-harboring ex-
oplanet would be only 20 pc away if simple life arose as
soon as it did on Earth in just 1% of TTPs around K
stars. Conversely, Earth would be the only life-hosting
planet in the solar neighborhood if abiogenesis was suc-
cessful in about 1-in-10,000 TTPs. If microbial life is
abundant it is also old, as it would have emerged more
than 8 Gyr ago in about one third of all life-bearing
planets today. Note how the convolution integral in
Equation (20) tends to smooth out the oscillations in
Ṅℓ compared to the star and planet formation rates de-
picted in Figure 7, and that the assumed abiogenesis
characteristic timescale of 1/λℓ = 1 Gyr shifts the me-
dian age of the ∼ 10, 000 P(ℓ|HZ) extrasolar biospheres
predicted in the solar neighborhood to 5.7 Gyr.
4.1. The Emergence of Oxygenic Atmospheres
A critical issue in the search for extraterrestrial life
is whether Earth-like conditions lead to ecosystems
11. Madau 11
that progressively oxygenate their planet atmospheres
roughly following Earth’s oxygenation history. The
first oxygenation of Earth’s atmosphere due to the
emergence of photosynthesizing cyanobacteria happened
about halfway through Earth’s history (Luo et al. 2016),
but O2 rose irreversibly to near present atmospheric lev-
els only about between 800 and 550 Myr ago, during
the Neoproterozoic Oxygenation Event (or NOE) (Lyons
et al. 2021; Och Shields-Zhou 2012), an event accom-
panied by major biological upgrades. While the precise
timing of the NOE remains subject of debate, our find-
ings inevitably invite the question of whether and how
often, given an habitable environment and following a
successful abiogenesis event, the conditions for the be-
ginnings of complex life may have arisen on exoplanets in
the solar neighborhood. We can then consider a second
stochastic process, labeled “O” for “oxygenation” and
defined by a rate parameter λO, which can proceed only
once abiogenesis (“ℓ”) is successful. The inverse of λO
is the characteristic timescale it takes for the earliest
forms of life to evolve and produce an NOE-like junc-
ture. Consider again an Earth-like planet that formed
at time t′
. The joint probability density that abiogen-
esis was first successful at time t′′
and was followed by
an oxygenation event at time t is then given by
pO(t′′
− t′
, t − t′′
) = λℓλO e−λℓ(t′′
−t′
)−λO(t−t′′
)
. (21)
The formation rate of simple life-hosting planets under-
going an NOE can then be written as
ṄO(t) = P(ℓ|HZ)
Z t
0
dt′′
Z t′′
0
dt′
Ṅ⊕(t′
)pO. (22)
We have integrated this equation assuming λ−1
O =
3.9 Gyr and plotted the results in Figure 8. Because
of the considerable delay between planet formation and
NOE, the ∼ 7500 P(ℓ|HZ) worlds with strong oxygenic
atmospheric biosignatures predicted to exist in the solar
neighborhood have a formation rate that peaked 5 Gyr
ago and a median age comparable to that of the solar
system.
5. SUMMARY AND DISCUSSION
The search for habitable exoplanets and extraterres-
trial life beyond Earth is one of the greatest scientific
endeavors of all time. The high frequency of terrestrial
planets in the habitable zones around dwarf stars im-
plied by Kepler observations makes it timely to develop
and explore new tools – beyond the probabilistic Drake
equation – for statistical exoplanet population and as-
trobiology studies that may help directing future mis-
sion designs and observational efforts. In particular, one
would like to understand – given a model of habitability
and biosignature genesis – the formation history of sim-
ple life-harboring environments in the local volume, and
identify how potential atmospheric biosignature yields
change as a function of stellar properties like age, mass,
and metallicity.
The approach we have described in this work is based
on a system of simple ODEs, rewritten below for the
convenience of the reader:
ṄK(t) = N⋆(t0)ψ(t)F,
Ż(t) = ψ(t)/g(Z),
ṄGP(t) = f(Z)ṄK,
Ṅ⊕(t) = η⊕θ(Z − Zc)ṄK,
Ṅℓ(t) = P(ℓ|HZ)
Z t
0
Ṅ⊕(t′
) λℓ e−λℓ(t−t′
)
dt′
,
ṄO(t) = P(ℓ|HZ)
Z t
0
dt′′
Z t′′
0
dt′
Ṅ⊕(t′
)pO,
(23)
which track the evolution of the mean number NK of
K-type stars in the solar neighborhood, their metal-
licity Z = Z(t), and the abundances NGP, N⊕, Nℓ,
and NO of giant planets, TTPs, life-harboring worlds,
and planets with oxygen-righ atmospheres, respectively
These rate equations provide a time-dependent map-
ping between star formation, metal enrichment, and
the occurrence of potentially habitable exoplanets over
the chemo-population history of the solar neighborhood,
and presents a useful basis for testing hypotheses about
Earth-like environments and life beyond the Solar sys-
tem. The new framework can be easily adapted to in-
corporate the hierarchy of astrophysical and biological
processes that regulate the age-dependent inventory of
any key planet population.
We have numerically integrated the equations above
adopting the recent tally of Nearby Stars (N⋆) and
white dwarfs from Gaia EDR3 (Gaia Collaboration et al.
2021), the episodic star formation history (ψ) of the so-
lar neighborhood as reconstructed by Alzate et al. (2021)
and Ruiz-Lara et al. (2020), the metallicity distribution
function (g) from the GALAH+TGAS spectroscopic
survey of dwarf stars in the solar galactic zone (Buder
et al. 2019), and assuming an age-metallicity relation.
In our model, the function f(Z) describes the metallic-
ity modulation of the occurrence rate of giant gaseous
planets (with integrated frequency today ηGP = 0.16,
Zhu Dong 2021), and we take η⊕ = 0.24 for the fidu-
cial occurrence rate of TTPs (Kopparapu et al. 2018)
around K-class stars on the ZAMS. There is a minimum
metallicity threshold for Earth-size planet formation of
Zc = 0.1 Z⊙ (Johnson Li 2012). Following earlier
12. 12 Beyond the Drake Equation
work (e.g. Spiegel Turner 2012), we describe abiogen-
esis as a stochastic Poisson process defined by a (uni-
form) rate parameter λℓ, and denote with P(ℓ|HZ) the
(constant) probability that a seemingly potentially hab-
itable planet in the HZ was at early times “Earth-like” in
a more detailed biochemical and geophysical sense and
eventually became inhabited by life. A second stochastic
process, an oxygenation event defined by a rate param-
eter λO, can proceed only once abiogenesis is successful.
Our main results can be summarized as follows:
1. The formation of exoplanets in the solar vicinity
followed two major events of enhanced star forma-
tion, starting with the emergence of the thick disk
about 11 Gyr ago and followed by a second event
that peaked 5.5 Gyr ago, lasted 3.5 Gyr, and pro-
duced more than 40% of all stars today. The solar
system formed in the second star formation surge
and was likely triggered by an external agent, per-
haps a merger with a gas-rich satellite galaxy (Mor
et al. 2019) or the first passage of the Sagittarius
dwarf galaxy through the Milky Way’s disk (Ruiz-
Lara et al. 2020);
2. Within 100 pc from the Sun, there are as many
as 11, 000 (η⊕/0.24) TTPs around K-type stars.
About 77% of all TTPs in the solar neighborhood
are older than the solar system;
3. The metallicity modulation of the giant planet oc-
currence rate results in a later typical formation
time, with TTPs vastly outnumbering giant plan-
ets at early times. Over the last 4 Gyr, the abun-
dance of TTPs around K stars has increased by
only +24%, while that of giant planets has dou-
bled. The existence of a fiducial metallicity floor
for the formation of terrestrial planets impacts
only a small fraction of the census population in
the solar neighborhood, as the vast majority of
star formation has taken place at Z 0.1 Z⊙;
4. The closest life-harboring Earth analog would be
less than 20 pc away if microbial life arose as soon
as it did on Earth in ∼
1% of the TTPs around
K stars. Conversely, Earth would be the only life-
hosting planet in the solar neighborhood if abio-
genesis was successful in about 1-in-10,000 TTPs.
If simple life is abundant (fast abiogenesis with
characteristic timescales 1/λℓ = 1 Gyr), it is also
old, as it would have emerged more than 8 Gyr
ago in about one third of all life-bearing planets
today.
We finally note that errors in the number counts of ex-
oplanets are likely dominated by planet occurrence rates
(ηGP and η⊕), which are uncertain at the ∼ 0.1–0.5 dex
level due to incompleteness in long-period candidates.
Comparable systematic errors may be associated with
uncertainties in the IMF, SFH, and metallicity effects.
Needless to say, in the case of life-hosting worlds, the
precise values of P(ℓ|HZ), λℓ, and λO are currently un-
known and remain a matter of speculation. Our work
says nothing about how difficult or easy abiogenesis re-
ally is, a question that must ultimately be answered em-
pirically. Still, given a model of habitability and biosig-
nature genesis, our approach may provide a blueprint
for assessing the prevalence of exoplanets and microbial
life-harboring worlds over the chemo-population history
of the solar neighborhood, gaining a sense of the atmo-
spheric biosignature yields among potential target stars
of different masses, ages, and metallicities, and guiding
future observational efforts and experiments.
ACKNOWLEDGEMENTS
Support for this work was provided by NASA through
grant 80NSSC21K027. We acknowledge useful discus-
sions on this project with J. Alzate, M. Bisazza, F.
Haardt, D. Lin, and R. Murray-Clay, and the hospitality
of New York University Abu Dhabi during the comple-
tion of this study. The author would also like to thank
the referee for a number of constructive comments and
suggestions that greatly improved the paper.
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