We have studied the conditions of through passage of asteroids with diameters 200, 100, and
50 m, consisting of three types of materials – iron, stone, and water ice, across the Earth’s
atmosphere with a minimum trajectory altitude in the range 10–15 km. The conditions of this
passage with a subsequent exit into outer space with the preservation of a substantial fraction
of the initial mass have been found. The results obtained support our idea explaining one of the
long-standing problems of astronomy – the Tunguska phenomenon, which has not received
reasonable and comprehensive interpretations to date. We argue that the Tunguska event was
caused by an iron asteroid body, which passed through the Earth’s atmosphere and continued
to the near-solar orbit.
Very regular high-frequency pulsation modes in young intermediate-mass starsSérgio Sacani
Asteroseismology probes the internal structures of stars by using their natural
pulsation frequencies1. It relies on identifying sequences of pulsation modes that can
be compared with theoretical models, which has been done successfully for many
classes of pulsators, including low-mass solar-type stars2, red giants3, high-mass stars4
and white dwarfs5. However, a large group of pulsating stars of intermediate mass—the
so-called δ Scuti stars—have rich pulsation spectra for which systematic mode
identification has not hitherto been possible6,7. This arises because only a seemingly
random subset of possible modes are excited and because rapid rotation tends to
spoil regular patterns8–10. Here we report the detection of remarkably regular
sequences of high-frequency pulsation modes in 60 intermediate-mass
main-sequence stars, which enables definitive mode identification. The space
motions of some of these stars indicate that they are members of known associations
of young stars, as confirmed by modelling of their pulsation spectra.
High-resolution UV/Optical/IR Imaging of Jupiter in 2016–2019Sérgio Sacani
Imaging observations of Jupiter with high spatial resolution were acquired beginning in 2016, with a cadence of 53
days to coincide with atmospheric observations of the Juno spacecraft during each perijove pass. The Wide Field
Camera 3 (WFC3) aboard the Hubble Space Telescope (HST) collected Jupiter images from 236 to 925 nm in 14
filters. The Near-Infrared Imager (NIRI) at Gemini North imaged Jovian thermal emission using a lucky-imaging
approach (co-adding the sharpest frames taken from a sequence of short exposures), using the M′ filter at 4.7 μm.
We discuss the data acquisition and processing and an archive collection that contains the processed WFC3 and
NIRI data (doi:10.17909/T94T1H). Zonal winds remain steady over time at most latitudes, but significant
evolution of the wind profile near 24°N in 2016 and near 15°S in 2017 was linked with convective superstorm
eruptions. Persistent mesoscale waves were seen throughout the 2016–2019 period. We link groups of lightning
flashes observed by the Juno team with water clouds in a large convective plume near 15°S and in cyclones near
35°N–55°N. Thermal infrared maps at the 10.8 micron wavelength obtained at the Very Large Telescope show
consistent high brightness temperature anomalies, despite a diversity of aerosol properties seen in the HST data.
Both WFC3 and NIRI imaging reveal depleted aerosols consistent with downwelling around the periphery of the
15°S storm, which was also observed by the Atacama Large Millimeter/submillimeter Array. NIRI imaging of
the Great Red Spot shows that locally reduced cloud opacity is responsible for dark features within the vortex. The
HST data maps multiple concentric polar hoods of high-latitude hazes.
A suppression of differential rotation in Jupiter’s deep interiorSérgio Sacani
Jupiter’s atmosphere is rotating differentially, with zones and
belts rotating at speeds that differ by up to 100 metres per
second. Whether this is also true of the gas giant’s interior has
been unknown1,2
, limiting our ability to probe the structure and
composition of the planet3,4
. The discovery by the Juno spacecraft
that Jupiter’s gravity field is north–south asymmetric5
and the
determination of its non-zero odd gravitational harmonics J3, J5, J7
and J9 demonstrates that the observed zonal cloud flow must persist
to a depth of about 3,000 kilometres from the cloud tops6
. Here we
report an analysis of Jupiter’s even gravitational harmonics J4, J6,
J8 and J10 as observed by Juno5
and compared to the predictions
of interior models. We find that the deep interior of the planet
rotates nearly as a rigid body, with differential rotation decreasing
by at least an order of magnitude compared to the atmosphere.
Moreover, we find that the atmospheric zonal flow extends to more
than 2,000 kilometres and to less than 3,500 kilometres, making
it fully consistent with the constraints obtained independently
from the odd gravitational harmonics. This depth corresponds
to the point at which the electric conductivity becomes large and
magnetic drag should suppress differential rotation7
. Given that
electric conductivity is dependent on planetary mass, we expect the
outer, differentially rotating region to be at least three times deeper
in Saturn and to be shallower in massive giant planets and brown
dwarfs.
Clusters of cyclones encircling Jupiter’s polesSérgio Sacani
The familiar axisymmetric zones and belts that characterize
Jupiter’s weather system at lower latitudes give way to pervasive
cyclonic activity at higher latitudes1
. Two-dimensional turbulence
in combination with the Coriolis β-effect (that is, the large
meridionally varying Coriolis force on the giant planets of the Solar
System) produces alternating zonal flows2
. The zonal flows weaken
with rising latitude so that a transition between equatorial jets and
polar turbulence on Jupiter can occur3,4
. Simulations with shallowwater
models of giant planets support this transition by producing
both alternating flows near the equator and circumpolar cyclones
near the poles5–9. Jovian polar regions are not visible from Earth
owing to Jupiter’s low axial tilt, and were poorly characterized by
previous missions because the trajectories of these missions did
not venture far from Jupiter’s equatorial plane. Here we report
that visible and infrared images obtained from above each pole
by the Juno spacecraft during its first five orbits reveal persistent
polygonal patterns of large cyclones. In the north, eight circumpolar
cyclones are observed about a single polar cyclone; in the south, one
polar cyclone is encircled by five circumpolar cyclones. Cyclonic
circulation is established via time-lapse imagery obtained over
intervals ranging from 20 minutes to 4 hours. Although migration of
cyclones towards the pole might be expected as a consequence of the
Coriolis β-effect, by which cyclonic vortices naturally drift towards
the rotational pole, the configuration of the cyclones is without
precedent on other planets (including Saturn’s polar hexagonal
features). The manner in which the cyclones persist without merging
and the process by which they evolve to their current configuration
are unknown.
Measurement of Jupiter’s asymmetric gravity fieldSérgio Sacani
The gravity harmonics of a fluid, rotating planet can be decomposed
into static components arising from solid-body rotation and dynamic
components arising from flows. In the absence of internal dynamics,
the gravity field is axially and hemispherically symmetric and is
dominated by even zonal gravity harmonics J2n that are approximately
proportional to qn, where q is the ratio between centrifugal
acceleration and gravity at the planet’s equator1
. Any asymmetry in the
gravity field is attributed to differential rotation and deep atmospheric
flows. The odd harmonics, J3, J5, J7, J9 and higher, are a measure of the
depth of the winds in the different zones of the atmosphere2,3
. Here
we report measurements of Jupiter’s gravity harmonics (both even
and odd) through precise Doppler tracking of the Juno spacecraft
in its polar orbit around Jupiter. We find a north–south asymmetry,
which is a signature of atmospheric and interior flows. Analysis of
the harmonics, described in two accompanying papers4,5
, provides
the vertical profile of the winds and precise constraints for the depth
of Jupiter’s dynamical atmosphere.
Jupiter’s atmospheric jet streams extend thousands of kilometres deepSérgio Sacani
The depth to which Jupiter’s observed east–west jet streams extend
has been a long-standing question1,2
. Resolving this puzzle has
been a primary goal for the Juno spacecraft3,4
, which has been in
orbit around the gas giant since July 2016. Juno’s gravitational
measurements have revealed that Jupiter’s gravitational field
is north–south asymmetric5
, which is a signature of the planet’s
atmospheric and interior flows6
. Here we report that the measured
odd gravitational harmonics J3, J5, J7 and J9 indicate that the
observed jet streams, as they appear at the cloud level, extend
down to depths of thousands of kilometres beneath the cloud level,
probably to the region of magnetic dissipation at a depth of about
3,000 kilometres7,8
. By inverting the measured gravity values into a
wind field9
, we calculate the most likely vertical profile of the deep
atmospheric and interior flow, and the latitudinal dependence of its
depth. Furthermore, the even gravity harmonics J8 and J10 resulting
from this flow profile also match the measurements, when taking
into account the contribution of the interior structure10. These
results indicate that the mass of the dynamical atmosphere is about
one per cent of Jupiter’s total mass
Very regular high-frequency pulsation modes in young intermediate-mass starsSérgio Sacani
Asteroseismology probes the internal structures of stars by using their natural
pulsation frequencies1. It relies on identifying sequences of pulsation modes that can
be compared with theoretical models, which has been done successfully for many
classes of pulsators, including low-mass solar-type stars2, red giants3, high-mass stars4
and white dwarfs5. However, a large group of pulsating stars of intermediate mass—the
so-called δ Scuti stars—have rich pulsation spectra for which systematic mode
identification has not hitherto been possible6,7. This arises because only a seemingly
random subset of possible modes are excited and because rapid rotation tends to
spoil regular patterns8–10. Here we report the detection of remarkably regular
sequences of high-frequency pulsation modes in 60 intermediate-mass
main-sequence stars, which enables definitive mode identification. The space
motions of some of these stars indicate that they are members of known associations
of young stars, as confirmed by modelling of their pulsation spectra.
High-resolution UV/Optical/IR Imaging of Jupiter in 2016–2019Sérgio Sacani
Imaging observations of Jupiter with high spatial resolution were acquired beginning in 2016, with a cadence of 53
days to coincide with atmospheric observations of the Juno spacecraft during each perijove pass. The Wide Field
Camera 3 (WFC3) aboard the Hubble Space Telescope (HST) collected Jupiter images from 236 to 925 nm in 14
filters. The Near-Infrared Imager (NIRI) at Gemini North imaged Jovian thermal emission using a lucky-imaging
approach (co-adding the sharpest frames taken from a sequence of short exposures), using the M′ filter at 4.7 μm.
We discuss the data acquisition and processing and an archive collection that contains the processed WFC3 and
NIRI data (doi:10.17909/T94T1H). Zonal winds remain steady over time at most latitudes, but significant
evolution of the wind profile near 24°N in 2016 and near 15°S in 2017 was linked with convective superstorm
eruptions. Persistent mesoscale waves were seen throughout the 2016–2019 period. We link groups of lightning
flashes observed by the Juno team with water clouds in a large convective plume near 15°S and in cyclones near
35°N–55°N. Thermal infrared maps at the 10.8 micron wavelength obtained at the Very Large Telescope show
consistent high brightness temperature anomalies, despite a diversity of aerosol properties seen in the HST data.
Both WFC3 and NIRI imaging reveal depleted aerosols consistent with downwelling around the periphery of the
15°S storm, which was also observed by the Atacama Large Millimeter/submillimeter Array. NIRI imaging of
the Great Red Spot shows that locally reduced cloud opacity is responsible for dark features within the vortex. The
HST data maps multiple concentric polar hoods of high-latitude hazes.
A suppression of differential rotation in Jupiter’s deep interiorSérgio Sacani
Jupiter’s atmosphere is rotating differentially, with zones and
belts rotating at speeds that differ by up to 100 metres per
second. Whether this is also true of the gas giant’s interior has
been unknown1,2
, limiting our ability to probe the structure and
composition of the planet3,4
. The discovery by the Juno spacecraft
that Jupiter’s gravity field is north–south asymmetric5
and the
determination of its non-zero odd gravitational harmonics J3, J5, J7
and J9 demonstrates that the observed zonal cloud flow must persist
to a depth of about 3,000 kilometres from the cloud tops6
. Here we
report an analysis of Jupiter’s even gravitational harmonics J4, J6,
J8 and J10 as observed by Juno5
and compared to the predictions
of interior models. We find that the deep interior of the planet
rotates nearly as a rigid body, with differential rotation decreasing
by at least an order of magnitude compared to the atmosphere.
Moreover, we find that the atmospheric zonal flow extends to more
than 2,000 kilometres and to less than 3,500 kilometres, making
it fully consistent with the constraints obtained independently
from the odd gravitational harmonics. This depth corresponds
to the point at which the electric conductivity becomes large and
magnetic drag should suppress differential rotation7
. Given that
electric conductivity is dependent on planetary mass, we expect the
outer, differentially rotating region to be at least three times deeper
in Saturn and to be shallower in massive giant planets and brown
dwarfs.
Clusters of cyclones encircling Jupiter’s polesSérgio Sacani
The familiar axisymmetric zones and belts that characterize
Jupiter’s weather system at lower latitudes give way to pervasive
cyclonic activity at higher latitudes1
. Two-dimensional turbulence
in combination with the Coriolis β-effect (that is, the large
meridionally varying Coriolis force on the giant planets of the Solar
System) produces alternating zonal flows2
. The zonal flows weaken
with rising latitude so that a transition between equatorial jets and
polar turbulence on Jupiter can occur3,4
. Simulations with shallowwater
models of giant planets support this transition by producing
both alternating flows near the equator and circumpolar cyclones
near the poles5–9. Jovian polar regions are not visible from Earth
owing to Jupiter’s low axial tilt, and were poorly characterized by
previous missions because the trajectories of these missions did
not venture far from Jupiter’s equatorial plane. Here we report
that visible and infrared images obtained from above each pole
by the Juno spacecraft during its first five orbits reveal persistent
polygonal patterns of large cyclones. In the north, eight circumpolar
cyclones are observed about a single polar cyclone; in the south, one
polar cyclone is encircled by five circumpolar cyclones. Cyclonic
circulation is established via time-lapse imagery obtained over
intervals ranging from 20 minutes to 4 hours. Although migration of
cyclones towards the pole might be expected as a consequence of the
Coriolis β-effect, by which cyclonic vortices naturally drift towards
the rotational pole, the configuration of the cyclones is without
precedent on other planets (including Saturn’s polar hexagonal
features). The manner in which the cyclones persist without merging
and the process by which they evolve to their current configuration
are unknown.
Measurement of Jupiter’s asymmetric gravity fieldSérgio Sacani
The gravity harmonics of a fluid, rotating planet can be decomposed
into static components arising from solid-body rotation and dynamic
components arising from flows. In the absence of internal dynamics,
the gravity field is axially and hemispherically symmetric and is
dominated by even zonal gravity harmonics J2n that are approximately
proportional to qn, where q is the ratio between centrifugal
acceleration and gravity at the planet’s equator1
. Any asymmetry in the
gravity field is attributed to differential rotation and deep atmospheric
flows. The odd harmonics, J3, J5, J7, J9 and higher, are a measure of the
depth of the winds in the different zones of the atmosphere2,3
. Here
we report measurements of Jupiter’s gravity harmonics (both even
and odd) through precise Doppler tracking of the Juno spacecraft
in its polar orbit around Jupiter. We find a north–south asymmetry,
which is a signature of atmospheric and interior flows. Analysis of
the harmonics, described in two accompanying papers4,5
, provides
the vertical profile of the winds and precise constraints for the depth
of Jupiter’s dynamical atmosphere.
Jupiter’s atmospheric jet streams extend thousands of kilometres deepSérgio Sacani
The depth to which Jupiter’s observed east–west jet streams extend
has been a long-standing question1,2
. Resolving this puzzle has
been a primary goal for the Juno spacecraft3,4
, which has been in
orbit around the gas giant since July 2016. Juno’s gravitational
measurements have revealed that Jupiter’s gravitational field
is north–south asymmetric5
, which is a signature of the planet’s
atmospheric and interior flows6
. Here we report that the measured
odd gravitational harmonics J3, J5, J7 and J9 indicate that the
observed jet streams, as they appear at the cloud level, extend
down to depths of thousands of kilometres beneath the cloud level,
probably to the region of magnetic dissipation at a depth of about
3,000 kilometres7,8
. By inverting the measured gravity values into a
wind field9
, we calculate the most likely vertical profile of the deep
atmospheric and interior flow, and the latitudinal dependence of its
depth. Furthermore, the even gravity harmonics J8 and J10 resulting
from this flow profile also match the measurements, when taking
into account the contribution of the interior structure10. These
results indicate that the mass of the dynamical atmosphere is about
one per cent of Jupiter’s total mass
We report the discovery of a new Kepler transiting circumbinary planet (CBP).
This latest addition to the still-small family of CBPs defies the current trend of known
short-period planets orbiting near the stability limit of binary stars. Unlike the previous
discoveries, the planet revolving around the eclipsing binary system Kepler-1647 has
a very long orbital period ( 1100 days) and was at conjunction only twice during
the Kepler mission lifetime. Due to the singular configuration of the system, Kepler-
1647b is not only the longest-period transiting CBP at the time of writing, but also one
of the longest-period transiting planets. With a radius of 1:060:01 RJup it is also the
largest CBP to date. The planet produced three transits in the light-curve of Kepler-
1647 (one of them during an eclipse, creating a syzygy) and measurably perturbed the
times of the stellar eclipses, allowing us to measure its mass to be 1:520:65 MJup.
The planet revolves around an 11-day period eclipsing binary consisting of two Solarmass
stars on a slightly inclined, mildly eccentric (ebin = 0:16), spin-synchronized
orbit. Despite having an orbital period three times longer than Earth’s, Kepler-1647b is
in the conservative habitable zone of the binary star throughout its orbit.
Beyond the Kuiper Belt Edge: New High Perihelion Trans-Neptunian Objects With...Sérgio Sacani
We are conducting a survey for distant solar system objects beyond the Kuiper
Belt edge ( 50 AU) with new wide-field cameras on the Subaru and CTIO tele-
scopes. We are interested in the orbits of objects that are decoupled from the
giant planet region in order to understand the structure of the outer solar sys-
tem, including whether a massive planet exists beyond a few hundred AU as first
reported in Trujillo and Sheppard (2014). In addition to discovering extreme
trans-Neptunian objects detailed elsewhere, we have found several objects with
high perihelia (q > 40 AU) that differ from the extreme and inner Oort cloud
objects due to their moderate semi-major axes (50 < a < 100 AU) and eccen-
tricities (e . 0.3). Newly discovered objects 2014 FZ71 and 2015 FJ345 have
the third and fourth highest perihelia known after Sedna and 2012 VP113, yet
their orbits are not nearly as eccentric or distant. We found several of these high
perihelion but moderate orbit objects and observe that they are mostly near Nep-
tune mean motion resonances and have significant inclinations (i > 20 degrees).
These moderate objects likely obtained their unusual orbits through combined
interactions with Neptune’s mean motion resonances and the Kozai resonance,
similar to the origin scenarios for 2004 XR190. We also find the distant 2008
ST291 has likely been modified by the MMR+KR mechanism through the 6:1
Neptune resonance. We discuss these moderately eccentric, distant objects along
with some other interesting low inclination outer classical belt objects like 2012
FH84 discovered in our ongoing survey.
Is there an_exoplanet_in_the_solar_systemSérgio Sacani
We investigate the prospects for the capture of the proposed Planet 9 from other
stars in the Sun’s birth cluster. Any capture scenario must satisfy three conditions:
the encounter must be more distant than ∼ 150 au to avoid perturbing the Kuiper
belt; the other star must have a wide-orbit planet (a & 100 au); the planet must be
captured onto an appropriate orbit to sculpt the orbital distribution of wide-orbit
Solar System bodies. Here we use N-body simulations to show that these criteria may
be simultaneously satisfied. In a few percent of slow close encounters in a cluster,
bodies are captured onto heliocentric, Planet 9-like orbits. During the ∼ 100 Myr
cluster phase, many stars are likely to host planets on highly-eccentric orbits with
apastron distances beyond 100 au if Neptune-sized planets are common and susceptible
to planet–planet scattering. While the existence of Planet 9 remains unproven, we
consider capture from one of the Sun’s young brethren a plausible route to explain such
an object’s orbit. Capture appears to predict a large population of Trans-Neptunian
Objects (TNOs) whose orbits are aligned with the captured planet, and we propose
that different formation mechanisms will be distinguishable based on their imprint on
the distribution of TNOs
A 2 4_determination_of_the_local_value_of_the_hubble_constantSérgio Sacani
We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to
reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%.
The bulk of this improvement comes from new, near-infrared observations of Cepheid
variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling
the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these
in turn leverage the magnitude-redshift relation based on 300 SNe Ia at z <0.15. All
19 hosts as well as the megamaser system NGC4258 have been observed with WFC3
in the optical and near-infrared, thus nullifying cross-instrument zeropoint errors in the
relative distance estimates from Cepheids. Other noteworthy improvements include a
33% reduction in the systematic uncertainty in the maser distance to NGC4258, a larger
sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to
the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of
Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW)
Cepheids.
TEMPORAL EVOLUTION OF THE HIGH-ENERGY IRRADIATION AND WATER CONTENT OF TRAPPI...Sérgio Sacani
The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could
harbour liquid water on their surfaces. UV observations are essential to measure their high-energy
irradiation, and to search for photodissociated water escaping from their putative atmospheres. Our
new observations of TRAPPIST-1 Ly-α line during the transit of TRAPPIST-1c show an evolution of
the star emission over three months, preventing us from assessing the presence of an extended hydrogen
exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history
of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the
orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape.
However, TRAPPIST-1e to h might have lost less than 3 Earth oceans if hydrodynamic escape stopped
once they entered the habitable zone. We caution that these estimates remain limited by the large
uncertainty on the planet masses. They likely represent upper limits on the actual water loss because
our assumptions maximize the XUV-driven escape, while photodissociation in the upper atmospheres
should be the limiting process. Late-stage outgassing could also have contributed significant amounts
of water for the outer, more massive planets after they entered the habitable zone. While our results
suggest that the outer planets are the best candidates to search for water with the JWST, they also
highlight the need for theoretical studies and complementary observations in all wavelength domains
to determine the nature of the TRAPPIST-1 planets, and their potential habitability.
Keywords: planetary systems - Stars: individual: TRAPPIST-1
The completeness-corrected rate of stellar encounters with the Sun from the f...Sérgio Sacani
I report on close encounters of stars to the Sun found in the first Gaia data release (GDR1). Combining Gaia astrometry with radial
velocities of around 320 000 stars drawn from various catalogues, I integrate orbits in a Galactic potential to identify those stars which
come within a few parsecs. Such encounters could influence the solar system, for example through gravitational perturbations of the
Oort cloud. 16 stars are found to come within 2 pc (although a few of these have dubious data). This is fewer than were found in a
similar study based on Hipparcos data, even though the present study has many more candidates. This is partly because I reject stars
with large radial velocity uncertainties (>10 km s−1
), and partly because of missing stars in GDR1 (especially at the bright end). The
closest encounter found is Gl 710, a K dwarf long-known to come close to the Sun in about 1.3 Myr. The Gaia astrometry predict
a much closer passage than pre-Gaia estimates, however: just 16 000 AU (90% confidence interval: 10 000–21 000 AU), which will
bring this star well within the Oort cloud. Using a simple model for the spatial, velocity, and luminosity distributions of stars, together
with an approximation of the observational selection function, I model the incompleteness of this Gaia-based search as a function
of the time and distance of closest approach. Applying this to a subset of the observed encounters (excluding duplicates and stars
with implausibly large velocities), I estimate the rate of stellar encounters within 5 pc averaged over the past and future 5 Myr to be
545±59 Myr−1
. Assuming a quadratic scaling of the rate within some encounter distance (which my model predicts), this corresponds
to 87 ± 9 Myr−1 within 2 pc. A more accurate analysis and assessment will be possible with future Gaia data releases.
T he effect_of_orbital_configuration)_on_the_possible_climates_and_habitabili...Sérgio Sacani
As lower-mass stars often host multiple rocky planets, gravitational interactions among planets can have significant
effects on climate and habitability over long timescales. Here we explore a specific case, Kepler-62f (Borucki et al.,
2013), a potentially habitable planet in a five-planet system with a K2V host star. N-body integrations reveal the
stable range of initial eccentricities for Kepler-62f is 0.00 £ e £ 0.32, absent the effect of additional, undetected
planets. We simulate the tidal evolution of Kepler-62f in this range and find that, for certain assumptions, the planet
can be locked in a synchronous rotation state. Simulations using the 3-D Laboratoire de Me´te´orologie Dynamique
(LMD) Generic global climate model (GCM) indicate that the surface habitability of this planet is sensitive to
orbital configuration.With 3 bar of CO2 in its atmosphere, we find that Kepler-62f would only be warm enough for
surface liquid water at the upper limit of this eccentricity range, providing it has a high planetary obliquity
(between 60 and 90). A climate similar to that of modern-day Earth is possible for the entire range of stable
eccentricities if atmospheric CO2 is increased to 5 bar levels. In a low-CO2 case (Earth-like levels), simulations
with version 4 of the Community Climate System Model (CCSM4) GCM and LMD Generic GCM indicate that
increases in planetary obliquity and orbital eccentricity coupled with an orbital configuration that places the
summer solstice at or near pericenter permit regions of the planet with above-freezing surface temperatures. This
may melt ice sheets formed during colder seasons. If Kepler-62f is synchronously rotating and has an ocean, CO2
levels above 3 bar would be required to distribute enough heat to the nightside of the planet to avoid atmospheric
freeze-out and permit a large enough region of open water at the planet’s substellar point to remain stable. Overall,
we find multiple plausible combinations of orbital and atmospheric properties that permit surface liquid water on
Kepler-62f. Key Words: Extrasolar planets—Habitability—Planetary environments. Astrobiology 16, xxx–xxx.
We present deep optical images of the Large and Small Magellanic Clouds (LMC and SMC) using
a low cost telephoto lens with a wide field of view to explore stellar substructure in the outskirts
of the stellar disk of the LMC (r < 10 degrees from the center). These data have higher resolution
than existing star count maps, and highlight the existence of stellar arcs and multiple spiral arms in
the northern periphery, with no comparable counterparts in the South. We compare these data to
detailed simulations of the LMC disk outskirts, following interactions with its low mass companion,
the SMC. We consider interaction in isolation and with the inclusion of the Milky Way tidal field.
The simulations are used to assess the origin of the northern structures, including also the low density
stellar arc recently identified in the DES data by Mackey et al. (2015) at ∼ 15 degrees. We conclude
that repeated close interactions with the SMC are primarily responsible for the asymmetric stellar
structures seen in the periphery of the LMC. The orientation and density of these arcs can be used to
constrain the LMC’s interaction history with and impact parameter of the SMC. More generally, we
find that such asymmetric structures should be ubiquitous about pairs of dwarfs and can persist for
1-2 Gyr even after the secondary merges entirely with the primary. As such, the lack of a companion
around a Magellanic Irregular does not disprove the hypothesis that their asymmetric structures are
driven by dwarf-dwarf interactions.
The importance of comets for the origin of life on Earth has been advocated for many decades. Amino acids are
key ingredients in chemistry, leading to life as we know it. Many primitive meteorites contain amino acids, and it
is generally believed that these are formed by aqueous alterations. In the collector aerogel and foil samples of the
Stardust mission after the flyby at comet Wild 2, the simplest form of amino acids, glycine, has been found
together with precursor molecules methylamine and ethylamine. Because of contamination issues of the samples,
a cometary origin was deduced from the 13C isotopic signature. We report the presence of volatile glycine
accompanied by methylamine and ethylamine in the coma of 67P/Churyumov-Gerasimenko measured by
the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) mass spectrometer, confirming the
Stardust results. Together with the detection of phosphorus and a multitude of organic molecules, this result
demonstrates that comets could have played a crucial role in the emergence of life on Earth.
The ASTRODEEP Frontier Fields catalogues II. Photometric redshifts and rest f...Sérgio Sacani
Aims. We present the first public release of photometric redshifts, galaxy rest frame properties and associated magnification values
in the cluster and parallel pointings of the first two Frontier Fields, Abell-2744 and MACS-J0416. The released catalogues aim to
provide a reference for future investigations of extragalactic populations in these legacy fields: from lensed high-redshift galaxies to
cluster members themselves.
Methods.We exploit a multiwavelength catalogue, ranging from Hubble Space Telescope (HST) to ground-based K and Spitzer IRAC,
which is specifically designed to enable detection and measurement of accurate fluxes in crowded cluster regions. The multiband
information is used to derive photometric redshifts and physical properties of sources detected either in the H-band image alone, or
from a stack of four WFC3 bands. To minimize systematics, median photometric redshifts are assembled from six dierent approaches
to photo-z estimates. Their reliability is assessed through a comparison with available spectroscopic samples. State-of-the-art lensing
models are used to derive magnification values on an object-by-object basis by taking into account sources positions and redshifts.
Results. We show that photometric redshifts reach a remarkable 3–5% accuracy. After accounting for magnification, the H-band
number counts are found to be in agreement at bright magnitudes with number counts from the CANDELS fields, while extending
the presently available samples to galaxies that, intrinsically, are as faint as H 32 33, thanks to strong gravitational lensing. The
Frontier Fields allow the galaxy stellar mass distribution to be probed, depending on magnification, at 0.5–1.5 dex lower masses with
respect to extragalactic wide fields, including sources at Mstar 107–108 M at z > 5. Similarly, they allow the detection of objects
with intrinsic star formation rates (SFRs) >1 dex lower than in the CANDELS fields reaching 0.1–1 M=yr at z 6–10.
Proper-motion age dating of the progeny of Nova Scorpii ad 1437Sérgio Sacani
‘Cataclysmic variables’ are binary star systems in which one
star of the pair is a white dwarf, and which often generate bright
and energetic stellar outbursts. Classical novae are one type of
outburst: when the white dwarf accretes enough matter from its
companion, the resulting hydrogen-rich atmospheric envelope
can host a runaway thermonuclear reaction that generates a rapid
brightening1–4. Achieving peak luminosities of up to one million
times that of the Sun5
, all classical novae are recurrent, on timescales
of months6
to millennia7
. During the century before and after an
eruption, the ‘novalike’ binary systems that give rise to classical
novae exhibit high rates of mass transfer to their white dwarfs8
.
Another type of outburst is the dwarf nova: these occur in binaries
that have stellar masses and periods indistinguishable from those
of novalikes9
but much lower mass-transfer rates10, when accretiondisk
instabilities11 drop matter onto the white dwarfs. The coexistence
at the same orbital period of novalike binaries and dwarf
novae—which are identical but for their widely varying accretion
rates—has been a longstanding puzzle9
. Here we report the recovery
of the binary star underlying the classical nova eruption of 11 March
ad 1437 (refs 12, 13), and independently confirm its age by propermotion
dating. We show that, almost 500 years after a classical-nova
event, the system exhibited dwarf-nova eruptions. The three other
oldest recovered classical novae14–16 display nova shells, but lack
firm post-eruption ages17,18, and are also dwarf novae at present.
We conclude that many old novae become dwarf novae for part of
the millennia between successive nova eruptions19,
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
We report the discovery of an optical Einstein Ring in the Sculptor constellation,
IAC J010127-334319, in the vicinity of the Sculptor Dwarf Spheroidal Galaxy. It is
an almost complete ring ( 300◦) with a diameter of 4.5 arcsec. The discovery was
made serendipitously from inspecting Dark Energy Camera (DECam) archive imaging
data. Confirmation of the object nature has been obtained by deriving spectroscopic
redshifts for both components, lens and source, from observations at the 10.4 m Gran
Telescopio CANARIAS (GTC) with the spectrograph OSIRIS. The lens, a massive
early-type galaxy, has a redshift of z = 0.581 while the source is a starburst galaxy
with redshift of z = 1.165. The total enclosed mass that produces the lensing effect
has been estimated to be Mtot = (1.86 ± 0.23) · 1012M⊙.
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
WHERE IS THE FLUX GOING? THE LONG-TERM PHOTOMETRIC VARIABILITY OF BOYAJIAN’S ...Sérgio Sacani
We present ∼ 800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the AllSky
Automated Survey for Supernovae (ASAS-SN) and ∼ 4000 days of monitoring from the All Sky
Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star
has steadily decreased at a rate of 6.3 ± 1.4 mmag yr−1
, such that the star is now 1.5% fainter than it
was in February 2015. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian’s
Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a
monotonic decline. We analyze a sample of ∼ 1000 comparison stars of similar brightness located in
the same ASAS-SN field and demonstrate that the recent fading is significant at & 99.4% confidence.
The 2015 − 2017 dimming rate is consistent with that measured with Kepler data for the time period
from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models
for the star’s behavior proposed to date
PROBING FOR EVIDENCE OF PLUMES ON EUROPA WITH HST/STISSérgio Sacani
Roth et al. (2014a) reported evidence for plumes of water venting from a southern high latitude
region on Europa – spectroscopic detection of off-limb line emission from the dissociation
products of water. Here, we present Hubble Space Telescope (HST) direct images of Europa in
the far ultraviolet (FUV) as it transited the smooth face of Jupiter, in order to measure absorption
from gas or aerosols beyond the Europa limb. Out of ten observations we found three in which
plume activity could be implicated. Two show statistically significant features at latitudes similar
to Roth et al., and the third, at a more equatorial location. We consider potential systematic
effects that might influence the statistical analysis and create artifacts, and are unable to find any
that can definitively explain the features, although there are reasons to be cautious. If the
apparent absorption features are real, the magnitude of implied outgassing is similar to that of the
Roth et al. feature, however the apparent activity appears more frequently in our data.
The 19 Feb. 2016 Outburst of Comet 67P/CG: An ESA Rosetta Multi-Instrument StudySérgio Sacani
On 19 Feb. 2016 nine Rosetta instruments serendipitously observed an outburst of gas and dust
from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras
and spectrometers ranging from UV over visible to microwave wavelengths, in-situ gas, dust and
plasma instruments, and one dust collector. At 9:40 a dust cloud developed at the edge of an image
in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature
of the outburst that signicantly exceeded the background. The enhancement ranged from 50% of
the neutral gas density at Rosetta to factors >100 of the brightness of the coma near the nucleus.
Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest
enhancements (factors >10). However, even the electron density at Rosetta increased by a factor 3
and consequently the spacecraft potential changed from 16V to 20V during the outburst. A
clear sequence of events was observed at the distance of Rosetta (34 km from the nucleus): within 15
minutes the Star Tracker camera detected fast particles ( 25 ms 1) while 100 m radius particles
were detected by the GIADA dust instrument 1 hour later at a speed of 6 ms 1. The slowest
were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst
originated just outside the FOV of the instruments, the source region and the magnitude of the
outburst could be determined.
Chemical interactions between Saturn’s atmosphere and its ringsSérgio Sacani
Past remote observations of
Saturn by Pioneer 11, Voyager 1 and 2, Earthbased
observatories, and the Cassini prime and
solstice missions suggested an inflow of water
from the rings to the atmosphere. This would
modify the chemistry of Saturn’s upper atmosphere
and ionosphere. In situ observations
during the Cassini Grand Finale provided an
opportunity to study this chemical interaction
We report the discovery of a new Kepler transiting circumbinary planet (CBP).
This latest addition to the still-small family of CBPs defies the current trend of known
short-period planets orbiting near the stability limit of binary stars. Unlike the previous
discoveries, the planet revolving around the eclipsing binary system Kepler-1647 has
a very long orbital period ( 1100 days) and was at conjunction only twice during
the Kepler mission lifetime. Due to the singular configuration of the system, Kepler-
1647b is not only the longest-period transiting CBP at the time of writing, but also one
of the longest-period transiting planets. With a radius of 1:060:01 RJup it is also the
largest CBP to date. The planet produced three transits in the light-curve of Kepler-
1647 (one of them during an eclipse, creating a syzygy) and measurably perturbed the
times of the stellar eclipses, allowing us to measure its mass to be 1:520:65 MJup.
The planet revolves around an 11-day period eclipsing binary consisting of two Solarmass
stars on a slightly inclined, mildly eccentric (ebin = 0:16), spin-synchronized
orbit. Despite having an orbital period three times longer than Earth’s, Kepler-1647b is
in the conservative habitable zone of the binary star throughout its orbit.
Beyond the Kuiper Belt Edge: New High Perihelion Trans-Neptunian Objects With...Sérgio Sacani
We are conducting a survey for distant solar system objects beyond the Kuiper
Belt edge ( 50 AU) with new wide-field cameras on the Subaru and CTIO tele-
scopes. We are interested in the orbits of objects that are decoupled from the
giant planet region in order to understand the structure of the outer solar sys-
tem, including whether a massive planet exists beyond a few hundred AU as first
reported in Trujillo and Sheppard (2014). In addition to discovering extreme
trans-Neptunian objects detailed elsewhere, we have found several objects with
high perihelia (q > 40 AU) that differ from the extreme and inner Oort cloud
objects due to their moderate semi-major axes (50 < a < 100 AU) and eccen-
tricities (e . 0.3). Newly discovered objects 2014 FZ71 and 2015 FJ345 have
the third and fourth highest perihelia known after Sedna and 2012 VP113, yet
their orbits are not nearly as eccentric or distant. We found several of these high
perihelion but moderate orbit objects and observe that they are mostly near Nep-
tune mean motion resonances and have significant inclinations (i > 20 degrees).
These moderate objects likely obtained their unusual orbits through combined
interactions with Neptune’s mean motion resonances and the Kozai resonance,
similar to the origin scenarios for 2004 XR190. We also find the distant 2008
ST291 has likely been modified by the MMR+KR mechanism through the 6:1
Neptune resonance. We discuss these moderately eccentric, distant objects along
with some other interesting low inclination outer classical belt objects like 2012
FH84 discovered in our ongoing survey.
Is there an_exoplanet_in_the_solar_systemSérgio Sacani
We investigate the prospects for the capture of the proposed Planet 9 from other
stars in the Sun’s birth cluster. Any capture scenario must satisfy three conditions:
the encounter must be more distant than ∼ 150 au to avoid perturbing the Kuiper
belt; the other star must have a wide-orbit planet (a & 100 au); the planet must be
captured onto an appropriate orbit to sculpt the orbital distribution of wide-orbit
Solar System bodies. Here we use N-body simulations to show that these criteria may
be simultaneously satisfied. In a few percent of slow close encounters in a cluster,
bodies are captured onto heliocentric, Planet 9-like orbits. During the ∼ 100 Myr
cluster phase, many stars are likely to host planets on highly-eccentric orbits with
apastron distances beyond 100 au if Neptune-sized planets are common and susceptible
to planet–planet scattering. While the existence of Planet 9 remains unproven, we
consider capture from one of the Sun’s young brethren a plausible route to explain such
an object’s orbit. Capture appears to predict a large population of Trans-Neptunian
Objects (TNOs) whose orbits are aligned with the captured planet, and we propose
that different formation mechanisms will be distinguishable based on their imprint on
the distribution of TNOs
A 2 4_determination_of_the_local_value_of_the_hubble_constantSérgio Sacani
We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to
reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%.
The bulk of this improvement comes from new, near-infrared observations of Cepheid
variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling
the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these
in turn leverage the magnitude-redshift relation based on 300 SNe Ia at z <0.15. All
19 hosts as well as the megamaser system NGC4258 have been observed with WFC3
in the optical and near-infrared, thus nullifying cross-instrument zeropoint errors in the
relative distance estimates from Cepheids. Other noteworthy improvements include a
33% reduction in the systematic uncertainty in the maser distance to NGC4258, a larger
sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to
the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of
Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW)
Cepheids.
TEMPORAL EVOLUTION OF THE HIGH-ENERGY IRRADIATION AND WATER CONTENT OF TRAPPI...Sérgio Sacani
The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could
harbour liquid water on their surfaces. UV observations are essential to measure their high-energy
irradiation, and to search for photodissociated water escaping from their putative atmospheres. Our
new observations of TRAPPIST-1 Ly-α line during the transit of TRAPPIST-1c show an evolution of
the star emission over three months, preventing us from assessing the presence of an extended hydrogen
exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history
of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the
orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape.
However, TRAPPIST-1e to h might have lost less than 3 Earth oceans if hydrodynamic escape stopped
once they entered the habitable zone. We caution that these estimates remain limited by the large
uncertainty on the planet masses. They likely represent upper limits on the actual water loss because
our assumptions maximize the XUV-driven escape, while photodissociation in the upper atmospheres
should be the limiting process. Late-stage outgassing could also have contributed significant amounts
of water for the outer, more massive planets after they entered the habitable zone. While our results
suggest that the outer planets are the best candidates to search for water with the JWST, they also
highlight the need for theoretical studies and complementary observations in all wavelength domains
to determine the nature of the TRAPPIST-1 planets, and their potential habitability.
Keywords: planetary systems - Stars: individual: TRAPPIST-1
The completeness-corrected rate of stellar encounters with the Sun from the f...Sérgio Sacani
I report on close encounters of stars to the Sun found in the first Gaia data release (GDR1). Combining Gaia astrometry with radial
velocities of around 320 000 stars drawn from various catalogues, I integrate orbits in a Galactic potential to identify those stars which
come within a few parsecs. Such encounters could influence the solar system, for example through gravitational perturbations of the
Oort cloud. 16 stars are found to come within 2 pc (although a few of these have dubious data). This is fewer than were found in a
similar study based on Hipparcos data, even though the present study has many more candidates. This is partly because I reject stars
with large radial velocity uncertainties (>10 km s−1
), and partly because of missing stars in GDR1 (especially at the bright end). The
closest encounter found is Gl 710, a K dwarf long-known to come close to the Sun in about 1.3 Myr. The Gaia astrometry predict
a much closer passage than pre-Gaia estimates, however: just 16 000 AU (90% confidence interval: 10 000–21 000 AU), which will
bring this star well within the Oort cloud. Using a simple model for the spatial, velocity, and luminosity distributions of stars, together
with an approximation of the observational selection function, I model the incompleteness of this Gaia-based search as a function
of the time and distance of closest approach. Applying this to a subset of the observed encounters (excluding duplicates and stars
with implausibly large velocities), I estimate the rate of stellar encounters within 5 pc averaged over the past and future 5 Myr to be
545±59 Myr−1
. Assuming a quadratic scaling of the rate within some encounter distance (which my model predicts), this corresponds
to 87 ± 9 Myr−1 within 2 pc. A more accurate analysis and assessment will be possible with future Gaia data releases.
T he effect_of_orbital_configuration)_on_the_possible_climates_and_habitabili...Sérgio Sacani
As lower-mass stars often host multiple rocky planets, gravitational interactions among planets can have significant
effects on climate and habitability over long timescales. Here we explore a specific case, Kepler-62f (Borucki et al.,
2013), a potentially habitable planet in a five-planet system with a K2V host star. N-body integrations reveal the
stable range of initial eccentricities for Kepler-62f is 0.00 £ e £ 0.32, absent the effect of additional, undetected
planets. We simulate the tidal evolution of Kepler-62f in this range and find that, for certain assumptions, the planet
can be locked in a synchronous rotation state. Simulations using the 3-D Laboratoire de Me´te´orologie Dynamique
(LMD) Generic global climate model (GCM) indicate that the surface habitability of this planet is sensitive to
orbital configuration.With 3 bar of CO2 in its atmosphere, we find that Kepler-62f would only be warm enough for
surface liquid water at the upper limit of this eccentricity range, providing it has a high planetary obliquity
(between 60 and 90). A climate similar to that of modern-day Earth is possible for the entire range of stable
eccentricities if atmospheric CO2 is increased to 5 bar levels. In a low-CO2 case (Earth-like levels), simulations
with version 4 of the Community Climate System Model (CCSM4) GCM and LMD Generic GCM indicate that
increases in planetary obliquity and orbital eccentricity coupled with an orbital configuration that places the
summer solstice at or near pericenter permit regions of the planet with above-freezing surface temperatures. This
may melt ice sheets formed during colder seasons. If Kepler-62f is synchronously rotating and has an ocean, CO2
levels above 3 bar would be required to distribute enough heat to the nightside of the planet to avoid atmospheric
freeze-out and permit a large enough region of open water at the planet’s substellar point to remain stable. Overall,
we find multiple plausible combinations of orbital and atmospheric properties that permit surface liquid water on
Kepler-62f. Key Words: Extrasolar planets—Habitability—Planetary environments. Astrobiology 16, xxx–xxx.
We present deep optical images of the Large and Small Magellanic Clouds (LMC and SMC) using
a low cost telephoto lens with a wide field of view to explore stellar substructure in the outskirts
of the stellar disk of the LMC (r < 10 degrees from the center). These data have higher resolution
than existing star count maps, and highlight the existence of stellar arcs and multiple spiral arms in
the northern periphery, with no comparable counterparts in the South. We compare these data to
detailed simulations of the LMC disk outskirts, following interactions with its low mass companion,
the SMC. We consider interaction in isolation and with the inclusion of the Milky Way tidal field.
The simulations are used to assess the origin of the northern structures, including also the low density
stellar arc recently identified in the DES data by Mackey et al. (2015) at ∼ 15 degrees. We conclude
that repeated close interactions with the SMC are primarily responsible for the asymmetric stellar
structures seen in the periphery of the LMC. The orientation and density of these arcs can be used to
constrain the LMC’s interaction history with and impact parameter of the SMC. More generally, we
find that such asymmetric structures should be ubiquitous about pairs of dwarfs and can persist for
1-2 Gyr even after the secondary merges entirely with the primary. As such, the lack of a companion
around a Magellanic Irregular does not disprove the hypothesis that their asymmetric structures are
driven by dwarf-dwarf interactions.
The importance of comets for the origin of life on Earth has been advocated for many decades. Amino acids are
key ingredients in chemistry, leading to life as we know it. Many primitive meteorites contain amino acids, and it
is generally believed that these are formed by aqueous alterations. In the collector aerogel and foil samples of the
Stardust mission after the flyby at comet Wild 2, the simplest form of amino acids, glycine, has been found
together with precursor molecules methylamine and ethylamine. Because of contamination issues of the samples,
a cometary origin was deduced from the 13C isotopic signature. We report the presence of volatile glycine
accompanied by methylamine and ethylamine in the coma of 67P/Churyumov-Gerasimenko measured by
the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) mass spectrometer, confirming the
Stardust results. Together with the detection of phosphorus and a multitude of organic molecules, this result
demonstrates that comets could have played a crucial role in the emergence of life on Earth.
The ASTRODEEP Frontier Fields catalogues II. Photometric redshifts and rest f...Sérgio Sacani
Aims. We present the first public release of photometric redshifts, galaxy rest frame properties and associated magnification values
in the cluster and parallel pointings of the first two Frontier Fields, Abell-2744 and MACS-J0416. The released catalogues aim to
provide a reference for future investigations of extragalactic populations in these legacy fields: from lensed high-redshift galaxies to
cluster members themselves.
Methods.We exploit a multiwavelength catalogue, ranging from Hubble Space Telescope (HST) to ground-based K and Spitzer IRAC,
which is specifically designed to enable detection and measurement of accurate fluxes in crowded cluster regions. The multiband
information is used to derive photometric redshifts and physical properties of sources detected either in the H-band image alone, or
from a stack of four WFC3 bands. To minimize systematics, median photometric redshifts are assembled from six dierent approaches
to photo-z estimates. Their reliability is assessed through a comparison with available spectroscopic samples. State-of-the-art lensing
models are used to derive magnification values on an object-by-object basis by taking into account sources positions and redshifts.
Results. We show that photometric redshifts reach a remarkable 3–5% accuracy. After accounting for magnification, the H-band
number counts are found to be in agreement at bright magnitudes with number counts from the CANDELS fields, while extending
the presently available samples to galaxies that, intrinsically, are as faint as H 32 33, thanks to strong gravitational lensing. The
Frontier Fields allow the galaxy stellar mass distribution to be probed, depending on magnification, at 0.5–1.5 dex lower masses with
respect to extragalactic wide fields, including sources at Mstar 107–108 M at z > 5. Similarly, they allow the detection of objects
with intrinsic star formation rates (SFRs) >1 dex lower than in the CANDELS fields reaching 0.1–1 M=yr at z 6–10.
Proper-motion age dating of the progeny of Nova Scorpii ad 1437Sérgio Sacani
‘Cataclysmic variables’ are binary star systems in which one
star of the pair is a white dwarf, and which often generate bright
and energetic stellar outbursts. Classical novae are one type of
outburst: when the white dwarf accretes enough matter from its
companion, the resulting hydrogen-rich atmospheric envelope
can host a runaway thermonuclear reaction that generates a rapid
brightening1–4. Achieving peak luminosities of up to one million
times that of the Sun5
, all classical novae are recurrent, on timescales
of months6
to millennia7
. During the century before and after an
eruption, the ‘novalike’ binary systems that give rise to classical
novae exhibit high rates of mass transfer to their white dwarfs8
.
Another type of outburst is the dwarf nova: these occur in binaries
that have stellar masses and periods indistinguishable from those
of novalikes9
but much lower mass-transfer rates10, when accretiondisk
instabilities11 drop matter onto the white dwarfs. The coexistence
at the same orbital period of novalike binaries and dwarf
novae—which are identical but for their widely varying accretion
rates—has been a longstanding puzzle9
. Here we report the recovery
of the binary star underlying the classical nova eruption of 11 March
ad 1437 (refs 12, 13), and independently confirm its age by propermotion
dating. We show that, almost 500 years after a classical-nova
event, the system exhibited dwarf-nova eruptions. The three other
oldest recovered classical novae14–16 display nova shells, but lack
firm post-eruption ages17,18, and are also dwarf novae at present.
We conclude that many old novae become dwarf novae for part of
the millennia between successive nova eruptions19,
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
We report the discovery of an optical Einstein Ring in the Sculptor constellation,
IAC J010127-334319, in the vicinity of the Sculptor Dwarf Spheroidal Galaxy. It is
an almost complete ring ( 300◦) with a diameter of 4.5 arcsec. The discovery was
made serendipitously from inspecting Dark Energy Camera (DECam) archive imaging
data. Confirmation of the object nature has been obtained by deriving spectroscopic
redshifts for both components, lens and source, from observations at the 10.4 m Gran
Telescopio CANARIAS (GTC) with the spectrograph OSIRIS. The lens, a massive
early-type galaxy, has a redshift of z = 0.581 while the source is a starburst galaxy
with redshift of z = 1.165. The total enclosed mass that produces the lensing effect
has been estimated to be Mtot = (1.86 ± 0.23) · 1012M⊙.
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
WHERE IS THE FLUX GOING? THE LONG-TERM PHOTOMETRIC VARIABILITY OF BOYAJIAN’S ...Sérgio Sacani
We present ∼ 800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the AllSky
Automated Survey for Supernovae (ASAS-SN) and ∼ 4000 days of monitoring from the All Sky
Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star
has steadily decreased at a rate of 6.3 ± 1.4 mmag yr−1
, such that the star is now 1.5% fainter than it
was in February 2015. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian’s
Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a
monotonic decline. We analyze a sample of ∼ 1000 comparison stars of similar brightness located in
the same ASAS-SN field and demonstrate that the recent fading is significant at & 99.4% confidence.
The 2015 − 2017 dimming rate is consistent with that measured with Kepler data for the time period
from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models
for the star’s behavior proposed to date
PROBING FOR EVIDENCE OF PLUMES ON EUROPA WITH HST/STISSérgio Sacani
Roth et al. (2014a) reported evidence for plumes of water venting from a southern high latitude
region on Europa – spectroscopic detection of off-limb line emission from the dissociation
products of water. Here, we present Hubble Space Telescope (HST) direct images of Europa in
the far ultraviolet (FUV) as it transited the smooth face of Jupiter, in order to measure absorption
from gas or aerosols beyond the Europa limb. Out of ten observations we found three in which
plume activity could be implicated. Two show statistically significant features at latitudes similar
to Roth et al., and the third, at a more equatorial location. We consider potential systematic
effects that might influence the statistical analysis and create artifacts, and are unable to find any
that can definitively explain the features, although there are reasons to be cautious. If the
apparent absorption features are real, the magnitude of implied outgassing is similar to that of the
Roth et al. feature, however the apparent activity appears more frequently in our data.
The 19 Feb. 2016 Outburst of Comet 67P/CG: An ESA Rosetta Multi-Instrument StudySérgio Sacani
On 19 Feb. 2016 nine Rosetta instruments serendipitously observed an outburst of gas and dust
from the nucleus of comet 67P/Churyumov-Gerasimenko. Among these instruments were cameras
and spectrometers ranging from UV over visible to microwave wavelengths, in-situ gas, dust and
plasma instruments, and one dust collector. At 9:40 a dust cloud developed at the edge of an image
in the shadowed region of the nucleus. Over the next two hours the instruments recorded a signature
of the outburst that signicantly exceeded the background. The enhancement ranged from 50% of
the neutral gas density at Rosetta to factors >100 of the brightness of the coma near the nucleus.
Dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest
enhancements (factors >10). However, even the electron density at Rosetta increased by a factor 3
and consequently the spacecraft potential changed from 16V to 20V during the outburst. A
clear sequence of events was observed at the distance of Rosetta (34 km from the nucleus): within 15
minutes the Star Tracker camera detected fast particles ( 25 ms 1) while 100 m radius particles
were detected by the GIADA dust instrument 1 hour later at a speed of 6 ms 1. The slowest
were individual mm to cm sized grains observed by the OSIRIS cameras. Although the outburst
originated just outside the FOV of the instruments, the source region and the magnitude of the
outburst could be determined.
Chemical interactions between Saturn’s atmosphere and its ringsSérgio Sacani
Past remote observations of
Saturn by Pioneer 11, Voyager 1 and 2, Earthbased
observatories, and the Cassini prime and
solstice missions suggested an inflow of water
from the rings to the atmosphere. This would
modify the chemistry of Saturn’s upper atmosphere
and ionosphere. In situ observations
during the Cassini Grand Finale provided an
opportunity to study this chemical interaction
Heterogeneous delivery of silicate and metal to the Earth by large planetesimalsSérgio Sacani
After the Moon’s formation, Earth experienced a protracted bombardment by leftover planetesimals. The mass delivered during
this stage of late accretion has been estimated to be approximately 0.5% of Earth’s present mass, based on highly siderophile
element concentrations in the Earth’s mantle and the assumption that all highly siderophile elements delivered by impacts
were retained in the mantle. However, late accretion may have involved mostly large (≥ 1,500 km in diameter)—and therefore
differentiated—projectiles in which highly siderophile elements were sequestered primarily in metallic cores. Here we present
smoothed-particle hydrodynamics impact simulations that show that substantial portions of a large planetesimal’s core may
descend to the Earth’s core or escape accretion entirely. Both outcomes reduce the delivery of highly siderophile elements to
the Earth’s mantle and imply a late accretion mass that may be two to five times greater than previously thought. Further, we
demonstrate that projectile material can be concentrated within localized domains of Earth’s mantle, producing both positive
and negative 182W isotopic anomalies of the order of 10 to 100 ppm. In this scenario, some isotopic anomalies observed in terrestrial
rocks can be explained as products of collisions after Moon formation.
Artigo relata como a Terra sofreu com os impactos de ateroides a 4 bilhões de anos atrás, e como a superfície do planeta foi remodelada e os oceanos formados.
Different Martian Crustal Seismic Velocities across the Dichotomy Boundary fr...Sérgio Sacani
Article This article is protected by copyright. All rights reserved.
Abstract
We have observed both minor-arc (R1) and major-arc (R2) Rayleigh waves for the largest marsquake (magnitude
of 4.7 ± 0.2) ever recorded. Along the R1 path (in the lowlands), inversion results show that a simple, two-layer
model with an interface located at 21 - 29 km and an upper crustal shear-wave velocity of 3.05 - 3.17 km/s can fit the
group velocity measurements. Along the R2 path, observations can be explained by upper crustal thickness models
constrained from gravity data and upper crustal shear-wave velocities of 2.61 - 3.27 km/s and 3.28 - 3.52 km/s in the
lowlands and highlands, respectively. The shear-wave velocity being faster in the highlands than in the lowlands
indicates the possible existence of sedimentary rocks, and relatively higher porosity in the lowlands.
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 provide an assessment of the threat posed by these X-ray
luminous SNe by analyzing the collective X-ray 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 of the emission and its full time evolution, and to
clarify the danger that these events pose for life in our Galaxy and other star-forming regions.
Micrometeoroid infall onto Saturn’s rings constrains their age to no more tha...Sérgio Sacani
There is ongoing debate as to whether Saturn’s main rings are relatively young or ancient— having been formed
shortly after Saturn or during the Late Heavy Bombardment. The rings are mostly water-ice but are polluted by
non-icy material with a volume fraction ranging from ∼0.1 to 2%. Continuous bombardment by micrometeoroids exogenic to the Saturnian system is a source of this non-icy material. Knowledge of the incoming mass flux
of these pollutants allows estimation of the rings’ exposure time, providing a limit on their age. Here we report
the final measurements by Cassini’s Cosmic Dust Analyzer of the micrometeoroid flux into the Saturnian system.
Several populations are present, but the flux is dominated by low-relative velocity objects such as from the
Kuiper belt. We find a mass flux between 6.9 · 10−17 and 2.7 · 10−16 kg m−2
s
−1 from which we infer a ring exposure time ≲100 to 400 million years in support of recent ring formation scenarios.
Lunar ejecta origin of near-Earth asteroid Kamo’oalewa is compatible with rar...Sérgio Sacani
Near-Earth asteroid, Kamo’oalewa (469219), is one of a small number of known quasisatellites of Earth; it transitions between quasi-satellite and horseshoe orbital states on
centennial timescales, maintaining this dynamics over megayears. The similarity of its
reflectance spectrum to lunar silicates and its Earth-like orbit both suggest that it originated
from the lunar surface. Here we carry out numerical simulations of the dynamical evolution of
particles launched from different locations on the lunar surface with a range of ejection
velocities in order to assess the hypothesis that Kamo‘oalewa originated as a debris-fragment
from a meteoroidal impact with the lunar surface. As these ejecta escape the Earth-Moon
environment, they face a dynamical barrier for entry into Earth’s co-orbital space. However, a
small fraction of launch conditions yields outcomes that are compatible with Kamo‘oalewa’s
orbit. The most favored conditions are launch velocities slightly above the escape velocity
from the trailing lunar hemisphere.
Investigating Coronal Holes and CMEs as Sources of Brightness Depletion Detec...Sérgio Sacani
The Parker Solar Probe (PSP) mission provides a unique opportunity to observe the solar corona from distances
below 20 R☉. In this work, we utilize white light images from the Wide-field Imager for Solar PRobe aboard the
PSP from solar encounters 10 through 13 to examine the causes of brightness depletions of the corona during the
rapid transit of PSP through the perihelia of its orbit. We analyze the effect of (1) coronal holes (CHs) and (2)
energetic coronal mass ejection (CME) events on the observed brightness of the images. We speculate on the
causes of the brightness depletions, ascribing them to the evacuation of (1) free electrons (reduced K-corona) and
(2) interplanetary dust (reduced F-corona). In particular, we show that (1) the presence of CHs in all of the orbits is
directly correlated with the depletion of the global white light emission recorded, and (2) a huge CME event in
encounter 13 caused a very deep depletion in its wake that removed the electron content as well as some of the
interplanetary dust.
Hot Earth or Young Venus? A nearby transiting rocky planet mysterySérgio Sacani
Venus and Earth provide astonishingly different views of the evolution of a rocky planet, raising the question of why these two rock y worlds evolv ed so differently. The recently disco v ered transiting Super-Earth LP 890-9c (TOI-4306c, SPECULOOS-2c) is a key to the question. It circles a nearby M6V star in 8.46 d. LP890-9c receives similar flux as modern Earth, which puts it very close to the inner edge of the Habitable Zone (HZ), where models differ strongly in their prediction of how long rocky planets can hold onto their water. We model the atmosphere of a hot LP890-9c at the inner edge of the HZ, where the planet could sustain several very different environments. The resulting transmission spectra differ considerably between a hot, wet exo-Earth, a steamy planet caught in a runaway greenhouse, and an exo-Venus. Distinguishing these scenarios from the planet’s spectra will provide critical new insights into the evolution of hot terrestrial planets into exo-Venus. Our model and spectra are available online as a tool to plan observations. They show that observing LP890-9c can provide key insights into the evolution of a rocky planet at the inner edge of the HZ as well as the long-term future of Earth.
The dynamic geophysical environment of (101955) Bennu based on OSIRIS-REx mea...Sérgio Sacani
The top-shaped morphology characteristic of asteroid (101955) Bennu, often found among fast-spinning asteroids and binary
asteroid primaries, may have contributed substantially to binary asteroid formation. Yet a detailed geophysical analysis of
this morphology for a fast-spinning asteroid has not been possible prior to the Origins, Spectral Interpretation, Resource
Identification, and Security-Regolith Explorer (OSIRIS-REx) mission. Combining the measured Bennu mass and shape obtained
during the Preliminary Survey phase of the OSIRIS-REx mission, we find a notable transition in Bennu’s surface slopes within
its rotational Roche lobe, defined as the region where material is energetically trapped to the surface. As the intersection of
the rotational Roche lobe with Bennu’s surface has been most recently migrating towards its equator (given Bennu’s increasing
spin rate), we infer that Bennu’s surface slopes have been changing across its surface within the last million years. We also find
evidence for substantial density heterogeneity within this body, suggesting that its interior is a mixture of voids and boulders.
The presence of such heterogeneity and Bennu’s top shape are consistent with spin-induced failure at some point in its past,
although the manner of its failure cannot yet be determined. Future measurements by the OSIRIS-REx spacecraft will provide
insight into and may resolve questions regarding the formation and evolution of Bennu’s top-shape morphology and its link to
the formation of binary asteroids.
The Expansion of the X-Ray Nebula Around η CarSérgio Sacani
The massive colliding wind binary system η Car is embedded in an X-ray emitting region having a characteristic
temperature of a few million degrees, associated with ejecta produced during the 1840s, and in earlier outbursts.
We use CHANDRA X-ray imaging observations obtained over the past two decades to directly measure the
expansion of the X-ray nebula for the first time. A combined CHANDRA/ACIS image shows a faint, nearly
uniform elliptic structure. This faint elliptical “shell” has a similar orientation and shape as the Homunculus nebula
but is about 3 times larger. We measure proper motions of brighter regions associated with the X-ray emitting ring.
We compare spectra of the soft X-ray emitting plasma in CHANDRA/ACIS and XMM-Newton PN observations
and show that the PN observations indicate a decline in X-ray flux which is comparable to that derived from
NICER observations. We associate the diffuse elliptical emission surrounding the bright X-ray “ring” with the blast
wave produced during the Great Eruption. We suggest that the interaction of this blast wave with pre-existing
clumps of ejecta produces the bright, broken X-ray emitting ring. We extrapolate the trend in X-ray energy back to
the time of the Great Eruption using a simple model and show that the X-ray energy was comparable to the kinetic
energy of the Homunculus, suggesting equipartition of energy between fast, low-density ejecta and slower, dense
ejecta.
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.
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.
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.
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.
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.
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.
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
Richard's entangled aventures in wonderlandRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Cancer cell metabolism: special Reference to Lactate PathwayAADYARAJPANDEY1
Normal Cell Metabolism:
Cellular respiration describes the series of steps that cells use to break down sugar and other chemicals to get the energy we need to function.
Energy is stored in the bonds of glucose and when glucose is broken down, much of that energy is released.
Cell utilize energy in the form of ATP.
The first step of respiration is called glycolysis. In a series of steps, glycolysis breaks glucose into two smaller molecules - a chemical called pyruvate. A small amount of ATP is formed during this process.
Most healthy cells continue the breakdown in a second process, called the Kreb's cycle. The Kreb's cycle allows cells to “burn” the pyruvates made in glycolysis to get more ATP.
The last step in the breakdown of glucose is called oxidative phosphorylation (Ox-Phos).
It takes place in specialized cell structures called mitochondria. This process produces a large amount of ATP. Importantly, cells need oxygen to complete oxidative phosphorylation.
If a cell completes only glycolysis, only 2 molecules of ATP are made per glucose. However, if the cell completes the entire respiration process (glycolysis - Kreb's - oxidative phosphorylation), about 36 molecules of ATP are created, giving it much more energy to use.
IN CANCER CELL:
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
introduction to WARBERG PHENOMENA:
WARBURG EFFECT Usually, cancer cells are highly glycolytic (glucose addiction) and take up more glucose than do normal cells from outside.
Otto Heinrich Warburg (; 8 October 1883 – 1 August 1970) In 1931 was awarded the Nobel Prize in Physiology for his "discovery of the nature and mode of action of the respiratory enzyme.
WARNBURG EFFECT : cancer cells under aerobic (well-oxygenated) conditions to metabolize glucose to lactate (aerobic glycolysis) is known as the Warburg effect. Warburg made the observation that tumor slices consume glucose and secrete lactate at a higher rate than normal tissues.
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
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.
(May 29th, 2024) Advancements in Intravital Microscopy- Insights for Preclini...Scintica Instrumentation
Intravital microscopy (IVM) is a powerful tool utilized to study cellular behavior over time and space in vivo. Much of our understanding of cell biology has been accomplished using various in vitro and ex vivo methods; however, these studies do not necessarily reflect the natural dynamics of biological processes. Unlike traditional cell culture or fixed tissue imaging, IVM allows for the ultra-fast high-resolution imaging of cellular processes over time and space and were studied in its natural environment. Real-time visualization of biological processes in the context of an intact organism helps maintain physiological relevance and provide insights into the progression of disease, response to treatments or developmental processes.
In this webinar we give an overview of advanced applications of the IVM system in preclinical research. IVIM technology is a provider of all-in-one intravital microscopy systems and solutions optimized for in vivo imaging of live animal models at sub-micron resolution. The system’s unique features and user-friendly software enables researchers to probe fast dynamic biological processes such as immune cell tracking, cell-cell interaction as well as vascularization and tumor metastasis with exceptional detail. This webinar will also give an overview of IVM being utilized in drug development, offering a view into the intricate interaction between drugs/nanoparticles and tissues in vivo and allows for the evaluation of therapeutic intervention in a variety of tissues and organs. This interdisciplinary collaboration continues to drive the advancements of novel therapeutic strategies.
Astronomy Update- Curiosity’s exploration of Mars _ Local Briefs _ leadertele...
On the possibility of through passage of asteroid bodies across the Earth’s atmosphere
1. MNRAS 493, 1344–1351 (2020) doi:10.1093/mnras/staa329
Advance Access publication 2020 February 4
On the possibility of through passage of asteroid bodies across the Earth’s
atmosphere
Daniil E. Khrennikov,1
Andrei K. Titov,2
Alexander E. Ershov,1,3
Vladimir I. Pariev4‹
and Sergei V. Karpov1,5,6‹
1Siberian Federal University, Svobodny Av. 79/10, Krasnoyarsk 660041, Russia
2Moscow Institute of Physics and Technology, Institusky Per. 9, Dolgoprudny 141700, Russia
3Institute of Computational Modeling SB RAS, Akademgorodok 50/44, Krasnoyarsk 660036, Russia
4P. N. Lebedev Physical Institute, Leninsky Prosp. 53, Moscow 119991, Russia
5L. V. Kirensky Institute of Physics, Federal Research Center KSC SB RAS, Akademgorodok 50/38, Krasnoyarsk 660036, Russia
6Siberian State University of Science and Technology, Krasnoyarsky Rabochy Av. 31, Krasnoyarsk 660014, Russia
Accepted 2020 January 15. Received 2020 January 12; in original form 2019 June 28
ABSTRACT
We have studied the conditions of through passage of asteroids with diameters 200, 100, and
50 m, consisting of three types of materials – iron, stone, and water ice, across the Earth’s
atmosphere with a minimum trajectory altitude in the range 10–15 km. The conditions of this
passage with a subsequent exit into outer space with the preservation of a substantial fraction
of the initial mass have been found. The results obtained support our idea explaining one of the
long-standing problems of astronomy – the Tunguska phenomenon, which has not received
reasonable and comprehensive interpretations to date. We argue that the Tunguska event was
caused by an iron asteroid body, which passed through the Earth’s atmosphere and continued
to the near-solar orbit.
Key words: meteorites, meteors, meteoroids – minor planets, asteroids: general.
1 INTRODUCTION
The problem of the motion in the Earth’s atmosphere of a large
space body (SB), capable of falling on to the surface of the planet in
the form of meteorites, is now of great interest. An equally urgent
concern is the study of the conditions for the passage of such bodies
through the upper atmosphere, even without collision with the
Earth’s surface, since the shock waves produced by this passage have
a colossal destructive effect (Loh 1963; Hawkins 1964; Martin 1966;
Bronshten 1983; Tom Gehrels 1994; Stulov, Mirskiy & Vyslyi 1995;
Nemchinov, Popova & Teterev 1999; Andruschenko, Syzranova &
Shevelev 2013; Morrison & Robertson 2019; Robertson & Mathias
2019).
Large SBs (1–10 km in size and larger) that carry the poten-
tial danger of collision with the Earth are detected by ordinary
astronomical observations. The bodies of intermediate dimensions
began to be registered relatively recently. Observations of such
bodies and the interpretation of observational data make it possible
to determine the probability of their collision with the Earth, their
properties, and the characteristic features of passage through the
atmosphere, as well as the consequences of fall. The clarification of
these questions will enable us to assess more accurately the degree
of asteroid hazard.
E-mail: vpariev@td.lpi.ru (VIP); karpov@iph.krasn.ru (SVK)
One of the fundamental problems of meteor physics is the
determination of the pre-atmospheric mass of SBs, since the
intensity of the meteor phenomenon is determined by the kinetic
energy of the body when entering the atmosphere of the planet.
It is known that the velocity of the bodies belonging to the Solar
system at the entrance to the Earth’s atmosphere should be inside
a relatively narrow range 11.2 < Vsn < 72.8 km s−1
(Bronshten
1983), so that the variance of the contribution of the velocity-
squared factor to the kinetic energy does not exceed 50 times. At
the same time, the mass of a meteor body can vary in a much wider
range: from fractions of a gram (micrometeor) to tens of millions of
tons or more (the Tunguska space body), that is, by 13–15 orders of
magnitude.
The goal of this paper is to evaluate the effect on the trajectory
of the SB of its passage through dense layers of the atmosphere,
taking into account the acting forces, the initial velocity, and the
mass and its variation during the flight, to determine the conditions
for possible passage of a large SB through the atmosphere with a
minimum loss of mass without collision with the Earth’s surface.
The obtained results are compared with observational data on the
Tunguska space body with an estimated altitude of maximum energy
release of about 10–15 km to receive evidence in favour of a
new explanation of the Tunguska phenomenon, which attributes
the absence of meteoritic material on the Earth’s surface near the
epicentre to the through passage of the SB across the atmosphere
with a small loss of velocity.
C 2020 The Author(s)
Published by Oxford University Press on behalf of the Royal Astronomical Society
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2. Passage of asteroid bodies 1345
Figure 1. Schematic diagram of the motion of a space body in the Earth’s
atmosphere and the angle of entry into the atmosphere (β) at a given point
relative to the X–Y coordinate system. Re is the radius of the Earth. Thickness
of the atmosphere is exaggerated. The trajectory of SB and its length within
the atmosphere are indicated by the line with the arrow.
2 PHYSICAL MODEL
First of all, let us imagine a model explaining the entry of the SB into
the Earth’s atmosphere with respect to the chosen X–Y coordinate
system coinciding with the centre of the Earth and corotating with
the rotation of the Earth (Fig. 1). The altitude of the entry of the SB
into the atmosphere is measured from the starting value h = 160 km,
at which the temperature of the SB begins to increase (Bronshten
1983). This layer of the atmosphere is indicated in Fig. 1 by the
value of h (the same parameter denotes the current altitude of SB
over the Earth’s surface). The angle of entry into the atmosphere
relative to the local horizontal line at the altitude h is one of the
most important parameters of the problem and is denoted by β.
We denote by L the length along the curved trajectory of SB in
the atmosphere, dL =
√
dX2 + dY2, and L = 0 corresponds to the
entry point of the SB into the atmosphere at h = 160 km.
2.1 The equation of motion with a variable mass
Ballistics of the SB are described by a system of equations, including
the equation of motion under the action of applied forces: the
force of the aerodynamic drag Ff and the gravitational force Fg =
Mg (Stulov et al. 1995):
M
dV
dt
= −
1
2
cdρhV 2
S
V
V
+ M g,
g = −
GMe
r3
r,
dr
dt
= V. (1)
Here M is the mass, V is the velocity of the body relative to the
Earth, t is time, G is the gravitational constant, g is the acceleration
of gravity, Me is the mass of the Earth, cd is the drag coefficient,
and ρh is the density of the atmosphere at altitude h (NASA 1976).
S is the area of the body’s middle cross-section, r is the current
radius vector, and r is the absolute value of the current radius vector
(the distance from the SB to the centre of the Earth). The time
dependence of M is implied in equations (1)–(3).
We note that the contribution of the lifting force to the ballistic
of the SB is also neglected in equation (1) because we assume
that the shape of the SB is close to spherical. The Coriolis and
centrifugal forces in the rotating reference frame are negligible
for fast-moving SBs compared to the aerodynamical forces from
stratospheric winds, which we also neglect here because SBs move
much faster than the wind speed.
In accordance with the existing ideas, e.g. Stulov et al. (1995),
the main contribution to the force of aerodynamic drag is made by
the difference in pressure between the frontal and rear parts of the
SB surface (low-pressure cavity forms near the rear surface). The
expression for the force of aerodynamic drag corresponds to the
first term in equation (1). The area S depends on the current mass
and size of SB (equation 2). In equation (2), the initial values of the
cross-sectional area and the mass of the SB are indicated as S0 and
M0:
S(t, M) = S0
M(t)
M0
μ
. (2)
We apply the simplified approach of isotropic loss of material
from the SB surface, which corresponds to the case μ = 2/3.
Determining the exponent μ is the subject of a separate study
(Bronshten 1983) taking into account the complexity of the problem
in a general case. The dependence S(t, M) is used in the numerical
solution of the differential equation (1) at each time iteration step
together with the change in the SB mass (see equation 3).
The value of the SB drag coefficient (Kutateladze 1990), in a
general case, depends on the Reynolds number Re = V R
ν
, where R
is the radius of SB and ν is the kinematic viscosity of the air. At a
velocity in the range 10 < V < 40 km s−1
, the radius of SB is of
the order of several dozens of metres, kinematic viscosity of air at
a trajectory altitude is of the order of 5 × 10−5
m2
s-1
and greater.
Therefore, the Reynolds number exceeds 1010
(Bronshten 1983).
According to Kutateladze (1990), Spearman & Braswell (1993),
and Zhdan et al. (2007), if the Reynolds number exceeds the value
1.5 × 105
, then a sharp drop of cd to 0.1 with a subsequent raise
on average of up to 0.9–1 takes place. In our case, the value of
cd = 0.9 corresponds to the most extreme conditions for the motion
of spherical SB in the atmosphere.
2.2 The loss of the space body mass and the heat transfer with
the shock wave boundary layer
The following equation describes the loss of SB mass when moving
in the atmosphere:
dM
dt
= −
chρhV 3
S
2H
. (3)
Here H is the specific heat of sublimation of the SB material and ch
is the coefficient of radiation heat transfer, defined as the fraction of
the kinetic energy of the oncoming stream of molecules that goes
into the sublimation of the SB material (Bronshten 1983).
Mass-loss of SB occurs due to heating to a temperature much
higher than the melting point (Stulov et al. 1995). In our case,
the main contributor to this heating is the radiant heat transfer
between the SB and the boundary layer of the shock wave, whose
temperature reaches several thousand degrees close to the surface
of the SB (Bronshten 1983). One of the most difficult problems
in calculating the radiant heat transfer is the determination of the
radiant heat transfer coefficient (ch). Its magnitude is affected by
the velocity of motion in the atmosphere, flight altitude, air density,
temperature of the boundary layer and the nature of the processes in
the boundary layer (dissociation and ionization of air molecules),
the degree of blackness of the radiating and absorbing surfaces, etc.
According to the available data, depending on the altitude and the
SB velocity, the values of the radiant heat transfer coefficient lie in
the range 0.01 ≤ ch ≤ 0.1 (Svetsov, Nemtchinov & Teterev 1995;
MNRAS 493, 1344–1351 (2020)
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3. 1346 D. E. Khrennikov et al.
Andruschenko et al. 2013; Johnson, Stern & Wheeller 2018) (the
maximum value is reached at an altitude of about 10 km). Taking
into account that the mass-loss rate reaches a maximum at ch = 0.1,
this value will be used in further calculations. According to Svetsov
et al. (1995), this value gives the best fit with observational data.
The degree of blackness for the radiating and absorbing surfaces
was taken to be equal to 1 in the calculations because of the
high temperature of the surfaces and the formation of a dense
high-temperature plasma (Bronshten 1983). The solution of the
system of differential equations (1) and (3) together with algebraic
equation (2) was carried out by the explicit Runge–Kutta method
of the fourth order.
Note that the employed model does not involve the process of SB
fragmentation (Stulov & Titova 2001; Barri 2010; Dudorov et al.
2015), since the initial dimensions of the SB are taken to be quite
significant (from 50 to 200 m) as well as moderate velocities, when
most of the SB remains intact, despite extreme external influences.
First of all, maximum resistance to fragmentation is characteristic
of iron SBs, which is associated with the high homogeneity of
their internal structure. In contrast to the iron SBs, the internal
structure of stone and ice SBs is heterogeneous with an abundance
of numerous microcracks. The results of the study of the conditions
for the fragmentation of iron SBs will be presented in our next
paper.
We denote the mass-loss by the term ‘ablation’, which includes
two processes: The first process is the low-temperature blowing off
a liquid film from the SB surface (at a temperature about 1000◦
C)
with the formation of small droplets. These droplets are typical
for a slow fall of small SBs or their fragments at the final stage
of the flight in the atmosphere. The second process is the high-
temperature sublimation of material occurring when the surface
temperature exceeds several thousand degrees. In this case, a mass-
loss occurs in the form of vapours of single atoms and their ions.
Under the conditions in consideration, the employed model includes
the sublimation as a dominant process responsible for the mass-loss
at high velocities – over 11.2 km s−1
.
3 RESULTS AND DISCUSSION
As a typical example of our calculations, Fig. 2 illustrates the results
of calculating the trajectory of the spherical iron SB with a radius
R = 50 m entering into the atmosphere at 20 km s-1
when passing
through it at the entry angle β = 11.◦
2 and a minimum altitude of
11 km. As can be seen from this figure, the perturbation of the
trajectory of the SB deviates it from the initial direction by an angle
α1 = 11.◦
25 when neglecting the aerodynamic drag effect and α1 =
16.◦
9 when the aerodynamic drag effect is taken into account. These
results demonstrate the significant effect of aerodynamic drag on
the SB trajectory.
Fig. 3 shows the dependence of the minimum trajectory altitude
for iron SBs with R = 100 m on the angle of entry into the atmo-
sphere for three velocities. Calculations did not reveal significant
differences for the SBs with radii R = 100, 50, and 25 m.
The complex pattern of aerodynamic fluxes around a spherical
SB, vortex formation, and stagnation zone in its rear part are
shown in Fig. 4. This figure demonstrates the extreme conditions
for the passage of a spherical SB through the dense layers of
the atmosphere as well as clearly shows the conditions for the
occurrence of the aerodynamic drag taking into account the structure
of fluxes in the stagnation zone. The results illustrated in Fig. 4
were obtained with the software package ANSYS FLUENT (Hutton
2017). This package is a universal software system of the finite-
Figure 2. Changes in the trajectory of SB during a through passage via the
atmosphere. The SB parameters are radius R = 50 m, the velocity of entry
into the atmosphere is 20 km s−1, and the minimum altitude is 11 km. The
angle of deflection α1 = 11.◦25 at cd = 0 and α2 = 16.◦9 at cd = 0.9. The
trajectory lengths correspond to the time moment 1000 s after the entrance
into the atmosphere.
Figure 3. Dependence of the minimum trajectory altitude on the entry angle
for the R = 100 m iron SB at different velocities.
volume method applied for solving various problems in aero- and
hydrodynamics (Hutton 2017). To calculate the pressure distribution
at the surface of an SB with the effect of air compression due to
pressure–density dependence, the FLUENT ‘ideal gas’ model was
used with the laminar flow regime. Zero static pressure was set to
absolute pressure 26 500 Pa at an altitude of 10 km (NASA 1976).
The default air temperature was set to 219 K.
Fig. 5 shows the trajectories of an SB at different angles of entry
into the atmosphere corresponding to the passage of SBs through the
atmosphere at different minimum altitudes over the Earth’s surface.
In this section, we present the results of calculations for bodies of
several sizes, consisting of iron, stone, and ice. Calculations were
carried out for the values of the radii of the SBs with R = 25,
50, and 100 m and for three materials: For iron, the specific heat of
sublimation of iron is H = 6380 kJ kg-1
(Luchinsky 1985), for stone,
H = 3965 kJ/kg for a specimen of lunar rock (Ahrens & O’Keefe
1971) and H = 9300 kJ kg-1
for quartz (Chirikhin 2011), and for
water ice, H = 2853 kJ kg-1
(Voitkovskiy 1999). In calculations with
a stone SB, we used a larger value of H for quartz, since SiO2 is
the basis of many natural minerals. The use of a smaller value of H
(3965 kJ kg-1
for lunar rock) results in an increase in the mass-loss
of stone SBs.
Figs 6 and 7 illustrate the mass-loss of an iron SB and its rate
when it is moving through the atmosphere at different velocities
and at a minimum trajectory altitude of 11 km. This altitude lies
MNRAS 493, 1344–1351 (2020)
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4. Passage of asteroid bodies 1347
Figure 4. (a): Distribution of the velocity modulus around a spherical SB
with radius R = 100 m; and (b): distribution of the velocity vectors.
Figure 5. The trajectories of the passage of SB through the atmosphere at
entry angles (β) in the range 5◦–12◦. Material is iron, radius of SB is R =
100 m, and initial velocity is 25 km s−1.
in the range of generally accepted values of the minimum altitude
for the Tunguska space body: 10–15 km (e.g. Bronshten 1983).
These dependencies are affected both by the velocity of SB, which
increases the loss of material, and by the time of flight through the
atmosphere, which reduces this loss.
Besides less loss of mass at lower velocity (15 km s−1
), we can
see the effect of lengthening of trajectory in the atmosphere from
3000 to 5000 km, which takes place for smaller size SBs as well
(Fig. 6f).
The main results of our calculation are presented in Table 1, which
can be considered as upper estimates of the residual masses of SBs
for different sizes and materials after through passage of the Earth’s
atmosphere for a trajectory length of 3000 km. As can be seen from
Table 1, the maximum fraction of the preserved mass is observed in
the iron SBs with a radius of 100 m at lower initial velocities. When
the velocities grow, the residual mass falls considerably. Similar
tendencies are observed for the stone SBs (without regard to their
fragmentation) with a significantly greater relative mass-loss. For
the case of ice SBs, at initial velocities higher than 15 km s−1
, a
Figure 6. Change in the residual mass of the iron SBs [M(L)] along the
trajectory through the atmosphere at two values of initial velocities and for
three SB radii. L is the length along the trajectory measured from the entry
point into the atmosphere at altitude h = 160 km. The curves end when
the SB reaches the exit point from the atmosphere at the same altitude h =
160 km. The minimum altitude hmin = 11 km and cd = 0.9.
complete loss of mass may take place. A faster mass-loss of stone
SBs compared to iron SBs of the same size is associated with a
lower mass of stone SBs due to much lower material density. That
is, if the amount of absorbed energy from the boundary layer of
shock wave is the same for equal sizes, then the fraction of the lost
mass (relative to the initial one) will be greater for the stone SB
compared to the iron one. Complete loss of mass of the ice SBs at
any initial velocities and sizes is explained by their low mass due to
low ice density. Another reason is a low specific heat of sublimation
of ice. Larger minimum altitudes of trajectory in calculations (hmin)
indicated in the table caption for stone and ice SBs were used to
prevent these SBs from falling.
Fig. 8 illustrates the variation of the velocity of SBs along the
trajectory with radii R = 100, 50, and 25 m. The calculations were
carried out with drag coefficient cd = 0.9 for a spherical body. The
obtained results show that the smaller the SB size, the higher the
deceleration. There is a more notable decrease in SB velocity with
a radius of 25 m in comparison with the radii of 100 and 50 m.
Fig. 8 contains a very important result for further consideration,
reflecting our conclusion that this dependence lies in the basis of
the mechanism of the SB tail formation when the fragmentation of
the SB occurs – the smaller the fragment and the lower its kinetic
energy, the greater its deceleration and the lower its final velocity
compared to larger fragments.
Fig. 9 demonstrates the changes in trajectories of the iron SB with
R = 25 m passing through the atmosphere with initial velocities 20
and 15 km s−1
and the effect of lengthening of the trajectory from
3000 to 5000 km at slower velocity and a minimum trajectory
altitude of 11 km. Both SBs exit the atmosphere but at different
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5. 1348 D. E. Khrennikov et al.
Figure 7. Change in the rate of the mass-loss of the iron SBs [dM(L)/dt]
along the trajectory through the atmosphere at two different initial velocities
and for three SB radii. The curves end when the SB exits from the atmosphere
at altitude h = 160 km. The minimum altitude hmin = 11 km and cd = 0.9.
moments of time. The effect of lengthening of the SB trajectory is
also shown in Fig. 6.
4 APPLICATION OF THE THROUGH PASSAGE
MODEL TO THE TUNGUSKA PHENOMENON
At present, there are over 100 hypotheses about the nature of
the Tunguska phenomenon, among which three to four versions
are predominant theories (e.g. Fesenkov 1962; Bronshten 2000a;
Farinella et al. 2001; Kundt 2003; Gladysheva 2008). They include
the fall on to the Earth of a small asteroid measuring several dozen
metres (Kundt 2003), consisting of typical asteroid materials, either
metal or stone, as well as ice, which is characteristic of cometary
nuclei (Fesenkov 1962; Bronshten 2000b; Morrison & Robertson
2019). The most probable material of the Tunguska SB mentioned
in literature is ice. According to the available observational data,
there are several variants of the direction and the trajectory length
of the Tunguska SB – from 450 to 600 km, in particular, with a
propagation direction from ‘south–north’ to ‘east–west’. The value
Figure 8. Changes in the velocity of the iron SBs along the trajectory when
passing through the atmosphere for the radii R = 100, 50, and 25 m at a
minimum altitude of 11 km (cd = 0.9). The curves end when the SB exits
from the atmosphere at an altitude h = 160 km.
Figure 9. Difference in the iron SB trajectories with radius R = 25 m when
passing through the atmosphere with two different initial velocities and a
minimum altitude of 11 km (cd = 0.9).
of the angle of entry into the atmosphere mentioned in literature is
30◦
–40◦
. The radius of the Tunguska SB was estimated based on the
amplitude of the shock wave recorded by the seismic stations and
amounted to about 25 m. The minimum trajectory altitude of the
Tunguska SB approximately corresponded to the point of maximum
energy release.
In Fig. 10, we show the results of comparative calculations of the
velocity variations of the iron, stone, and ice SBs with radii 100 and
50 m along the trajectory of through passage across the atmosphere
for an initial velocity of 20 km s−1
. Stone SBs lose their velocity
faster than iron SBs and ice SBs do not survive passage through the
atmosphere.
In Fig. 11, we demonstrate an unusual trajectory of a stone SB
with R = 50 m compared to an iron one with the same size. At point
1, the SB penetrates the atmosphere at altitude 160 km, at point 2,
it reaches the minimum altitude of 11 km, at point 3, it exits the
atmosphere at altitude 160 km with a subsequent re-entry due to a
significant decrease in velocity, and at point 4, it is near the point of
fall. There is a considerable lengthening of trajectory of the stone
SB compared to the iron body, which passes through the atmosphere
Table 1. The ratios of the preserved mass of SB Mout to the initial mass Min for different materials
at different initial velocities V and initial sizes R. Calculations are performed for minimum altitude
hmin = 11 km, except for the stone SB with R = 25 m (hmin = 18 km), and for the ice SBs with radii
R = 100, 50, and 25 m with corresponding hmin = 18, 23, and 28 km.
Material Iron Stone Ice
R (m) 100 50 25 100 50 25 100 50 25
Mout/Min (V = 15 km s-1) 0.69 0.48 0.25 0.49 0.32 0.3 0.017 0.014 0.01
Mout/Min (V = 20 km s-1) 0.52 0.27 0.08 0.298 0.11 0.1 0 0 0
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6. Passage of asteroid bodies 1349
Figure 10. Comparative variation of the velocity of the iron, stone, and
ice SBs along the trajectory with R = 100 m (a) and R = 50 m (b). The
initial velocity 20 km s−1 and the minimum trajectory altitude is 11 km.
The curves for iron and stone SBs in panel (a) end when the SB exits the
atmosphere at an altitude h = 160 km. The curves for ice SBs end when the
mass of the SBs vanishes completely. The long curve for the stone SB in
panel (b) corresponds to an unusually long trajectory of the stone SB shown
in Fig. 11.
Figure 11. The trajectory of a stone SB with radius R = 50 m. Initial
velocity is V = 20 km s−1 and minimum altitude is 11 km. At point 1:
V = 20 km s-1, relative mass M/Min = 1, and h = 160 km; at point 2: V =
14.2 km s-1, M/Min = 0.3, and h = 11.26 km; at point 3: V = 7.6 km s-1,
M/Min = 0.13, and h = 159.7 km; at point 4: V = 5.9 km s-1, M/Min = 0.11,
and h = 11 km (with a subsequent fall). The inset shows the comparison of
trajectories of the stone and iron SBs with an equal radius R = 50 m.
with a minimum loss of velocity and minimum deflection due to a
high initial mass (its trajectory is shown in the inset). Although quite
improbable, such an SB could manifest itself as a pair of explosive
phenomena in the atmosphere separated by thousands of kilometres
in distance and tens of minutes in time.
Fig. 12 shows trajectories of an ice SB with R = 100 m at
different entry angles and changes in mass. This figure demonstrates
Figure 12. Variation of the ice SB mass along the trajectory with an
initial velocity 20 km s−1 and an entry angle in the range 10◦ ≤ β ≤
15◦ for different minimum altitudes of the trajectory. The initial SB radius is
100 m.
Figure 13. Variation of the ice SB mass along the trajectory of fall with an
initial velocity 25 and 15 km s−1 and entry angle 30◦.
a dramatic loss of mass at angles over 11◦
. At angle 10◦
, the initial
mass is preserved due to the high altitude – over 50 km (Fig. 3).
Fig. 13 shows the reduction of the masses of ice SBs with
R = 100, 50, and 25 m on the trajectory of collision with the
surface of the Earth. The residual fractions of the mass at an initial
velocity of 15 km s −1
are 49 per cent, 21.3 per cent, and 4.8 per cent,
respectively, for radii R = 100, 50, and 25 m of the SBs. The length
of the trajectory until the moment of the collision with the surface
of the Earth is about 325 km for the initial velocity of 15 km s -1
.
At an entry velocity of 25 km s−1
for radii R = 100 and 50 m, SBs
fall with a preservation of 6 per cent and 0.000 04 per cent of the
initial mass respectively. For radius R = 25 m and entry velocity
of 25 km s −1
, an ice SB loses all its mass completely within a
trajectory length of about 329 km.
Of course, the fall of SB with preservation of a significant part of
the initial mass results in the formation of a crater with a diameter
larger than 1 km (Stulov et al. 1995). But the fact is that there
are no craters near the epicentre and around. The actual length
of the trajectory based on the results of visual observations was
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7. 1350 D. E. Khrennikov et al.
estimated to be about 450–700 km, which is over 1.5 times longer
than the calculated value for the ice SB. Therefore, the hypothesis
of the ice origin of the Tunguska SB, which enters the atmosphere
at an angle β = 30◦
–40◦
, is hardly justified from this point of
view.
Moreover, Fig. 12 shows the decrease in the mass of the ice SB
with an initial radius of 100 m along the trajectory at small angles
of entry into the atmosphere. As can be seen from the figure, the
passage of the ice SB through the atmosphere while preserving a
significant fraction of mass is possible only at a minimum altitude
above 40 km, which contradicts with the estimated minimum
altitude of about 10–15 km in the Tunguska event.
Our calculations showed that the trajectory length of the ice SB
when it passes through the atmosphere at a minimum altitude of
15.5 km and small entry angles (less than 15◦
) until the moment of its
complete loss of mass even at a radius of 100 m is two times shorter
compared to the case of the iron SB. Thus, the through passage of
the ice SB at small entry angles with a minimum trajectory altitude
10–15 km is impossible.
For the ice SB with a radius of 25 m, the length of the trajectory to
the moment of the total loss of mass is reduced by four to five times.
In addition, it was shown that a considerable part of the initial mass
is preserved by iron and stone SBs with radii of 100, 50, and 25 m
at an entry angle of 30◦
. But their fall would be accompanied by the
formation of craters with a diameter larger than 1 km and a depth
over 200 m.
As the final comments, which can be considered as the plan
for future research, we can mention the following problems. In
our work, we did not deal with the problem of the formation of a
shock wave, although when comparing the Tunguska phenomenon
with the Chelyabinsk meteorite with a size of about 10 m and an
altitude of maximum energy release of about 30 km, we have no
reason to doubt that the body that is 10–20 times larger with an
altitude of maximum energy release of 10–15 km at a velocity
of 20 km s−1
will create a shock wave with a huge amplitude
and destructive force, capable of causing tree-fall over an area
exceeding 1600 km2
. Experimental modelling of the knock-down
effect of a shock wave from the source with cylindrical geometry
was performed by Zotkin & Tsikulin (1966). The cylindrical source
of the shock wave was modelled by a long detonating cord inclined
at a certain angle to a plane planted with small sticks, which
imitated trees in the Siberian forest. It was shown that the shape
of the area of fallen sticks was similar to the shape of real tree-
fall territory. However, Zotkin & Tsikulin (1966) did not model
the dependence of the strength of the cylindrical shock wave on
the height of its source above the ground. Instead, they added a
point explosive at the lower end of their cord to model a presumed
spherical component of the shock wave. Because rates of the
mass and energy losses of the SB that caused the Tunguska event
depend strongly on its altitude above the ground (as evident from
Fig. 7), a sharp increase in energy release close to the minimum
altitude reached by the through passing SB can be interpreted as
an explosion creating a spherical component of the shock wave.
Clearly, making a detailed prediction for the patterns of tree-fall
in the framework of our hypothesis of a through-passed SB as a
cause for the Tunguska event will be an important subject of future
research.
In solving the main problems in this work, we confined ourselves
to the need to make an upper estimate for calculating the residual
mass of space body using the parameters maximizing the mass-
loss. Finally, in this paper, we did not consider the problem of the
mass-loss of the space body due to its fragmentation. This will
be the subject of future research and the results will be published
elsewhere (Khrennikov et al. 2020).
5 SUMMARY
Based on the obtained results, we can make the following state-
ments:
(i) The conditions for the possible through passage of a large
space body composed of various materials across the Earth’s
atmosphere with a minimal loss of mass and without collision with
the surface of the planet are established. It was shown that this
corresponds to the entry angles of space body into the atmosphere
β ≤ 11.◦
5.
(ii) It was shown that the Tunguska space body could hardly
consist of ice, since the length of the trajectory of such a body in the
atmosphere before the complete loss of its mass would be less than
the length of its trajectory estimated on the basis of observational
data. This statement is valid for estimates performed for the value
of the radiation heat transfer coefficient ch = 0.1 as well as making
allowance for uncertainties and variations of the values mentioned
in the literature.
(iii) The value of the angle of entry into the atmosphere of 30◦
–
40◦
mentioned in the literature for the Tunguska space body looks
unrealistic, since it corresponds to the trajectory of a fall of a
body with a large residual mass and trajectory length, which is
1.5–2 times shorter than the estimated trajectory length based on
the observational data. Such a fall would be accompanied by the
formation of a large crater, absent near the epicentre and around.
(iv) Probably, the most realistic version explaining the Tunguska
phenomenon is the through passage of the iron asteroid body as the
most resistible to fragmentation across the Earth’s atmosphere at a
minimum altitude of 10–15 km with the length of the trajectory in
the atmosphere of about 3000 km and a subsequent exit of this
asteroid body into the outer space to the near-solar orbit. This
version is supported by the fact that there are no remnants of this
body and craters on the surface of the Earth. Within this version,
we can explain optical effects associated with a strong dustiness of
high layers of the atmosphere over Europe, which caused a bright
glow of the night sky.
If we admit the version of the complete loss of mass of SB after
the passage of the epicentre or close to it, then the evidence of
its reality would be the presence of droplets of meteoric iron of
millimetre sizes on the Earth’s surface along the trajectory of SB
and around. It follows from Fig. 8 that the smaller the SB size
and its mass are, the faster it loses a velocity (the amplitude of the
shock wave near the epicentre also becomes smaller). Finally, when
the velocity of a diminishing SB reduces to such an extent that
its surface temperature approaches 1000◦
C, the sublimation ceases
and the dominant mechanism of mass-loss consists of blowing off
a liquid film from the surface of the body. In this case, the SB
becomes the source of a huge amount of droplets, which will
be sprayed by the SB. However, such microformations have not
been found despite intensive searches around the epicentre and
far beyond. The absence of iron droplets around the epicentre is
explained by the high velocity of the SB during through passage
across the Earth’ s atmosphere – always over 11.2 km s−1
when the
surface temperature exceeds several thousands of degree Celcius.
The dominant mechanism of mass-loss at these temperatures is the
sublimation of material in the form of single atoms, which can be
found on the Earth’s surface as iron oxides, which do not differ from
the same widespread iron oxides of terrestrial origin.
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8. Passage of asteroid bodies 1351
ACKNOWLEDGEMENTS
Authors thank A. B. Klyuchantsev for aerodynamic calculations
with the software package ANSYS FLUENT. The manuscript bene-
fited from many suggestions and comments made in the constructive
report by the reviewer, Dr Darrel Robertson, whom we thank for
careful reading of the manuscript. We are grateful to Doug Black
of Hamilton, Canada, for correcting the English in the final version
of the manuscript.
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