This is a powerpoint presentation that is about one of the Senior High School Core Subject: Earth and Life Science. It is composed of the theories that explains the Earth and its Subsystems (The Four Spheres).
This is a powerpoint presentation that is about one of the Senior High School Core Subject: Earth and Life Science. It is composed of the theories that explains the Earth and its Subsystems (The Four Spheres).
What information from Mars can the astronauts obtain? Describe the condition of the Mars environment. Some scientists discuss the possibility to use greenhouse gas on the atmosphere of planet Mars, to make it habitable. Do you approve of this idea?
In this lecture you will be introduced to Earth system science a new holisitic approach to studying the Earth as a whole system of many interacting parts.
This article presents how planet Earth was born, how it operates and how it is protected from threats coming from outer space. In addition to showing how the Earth operates as a dynamic system, it shows how our planet will disappear completely when the Sun migrates out of Earth's orbit in about 1 billion years.
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.
Extensive Noachian fluvial systems in Arabia Terra: Implications for early Ma...Sérgio Sacani
Valley networks are some of the strongest lines of evidence for
extensive fluvial activity on early (Noachian; >3.7 Ga) Mars. However,
their purported absence on certain ancient terrains, such as
Arabia Terra, is at variance with patterns of precipitation as predicted
by “warm and wet” climate models. This disagreement has contributed
to the development of an alternative “icy highlands” scenario,
whereby valley networks were formed by the melting of highland ice
sheets. Here, we show through regional mapping that Arabia Terra
shows evidence for extensive networks of sinuous ridges. We interpret
these ridge features as inverted fluvial channels that formed in
the Noachian, before being subject to burial and exhumation. The
inverted channels developed on extensive aggrading flood plains. As
the inverted channels are both sourced in, and traverse across, Arabia
Terra, their formation is inconsistent with discrete, localized sources
of water, such as meltwater from highland ice sheets. Our results are
instead more consistent with an early Mars that supported widespread
precipitation and runoff.
Choose/Create an Alien Planet(Powerpoint Quiz)Jack Smith
This interactive powerpoint uses hyperlinks to create a quiz. This allows you to input information about a planet by answering the three questions, and then have one of 27 custom planets be selected for you. Originally made for a science project/report
What information from Mars can the astronauts obtain? Describe the condition of the Mars environment. Some scientists discuss the possibility to use greenhouse gas on the atmosphere of planet Mars, to make it habitable. Do you approve of this idea?
In this lecture you will be introduced to Earth system science a new holisitic approach to studying the Earth as a whole system of many interacting parts.
This article presents how planet Earth was born, how it operates and how it is protected from threats coming from outer space. In addition to showing how the Earth operates as a dynamic system, it shows how our planet will disappear completely when the Sun migrates out of Earth's orbit in about 1 billion years.
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.
Extensive Noachian fluvial systems in Arabia Terra: Implications for early Ma...Sérgio Sacani
Valley networks are some of the strongest lines of evidence for
extensive fluvial activity on early (Noachian; >3.7 Ga) Mars. However,
their purported absence on certain ancient terrains, such as
Arabia Terra, is at variance with patterns of precipitation as predicted
by “warm and wet” climate models. This disagreement has contributed
to the development of an alternative “icy highlands” scenario,
whereby valley networks were formed by the melting of highland ice
sheets. Here, we show through regional mapping that Arabia Terra
shows evidence for extensive networks of sinuous ridges. We interpret
these ridge features as inverted fluvial channels that formed in
the Noachian, before being subject to burial and exhumation. The
inverted channels developed on extensive aggrading flood plains. As
the inverted channels are both sourced in, and traverse across, Arabia
Terra, their formation is inconsistent with discrete, localized sources
of water, such as meltwater from highland ice sheets. Our results are
instead more consistent with an early Mars that supported widespread
precipitation and runoff.
Choose/Create an Alien Planet(Powerpoint Quiz)Jack Smith
This interactive powerpoint uses hyperlinks to create a quiz. This allows you to input information about a planet by answering the three questions, and then have one of 27 custom planets be selected for you. Originally made for a science project/report
Venusian Habitable Climate Scenarios: Modeling Venus Through Time and Applica...Sérgio Sacani
One popular view of Venus' climate history describes a world that has spent much of its life
with surface liquid water, plate tectonics, and a stable temperate climate. Part of the basis for this
optimistic scenario is the high deuterium to hydrogen ratio from the Pioneer Venus mission that was
interpreted to imply Venus had a shallow ocean's worth of water throughout much of its history. Another
view is that Venus had a long-lived (∼100 million years) primordial magma ocean with a CO2 and steam
atmosphere. Venus' long-lived steam atmosphere would sufficient time to dissociate most of the water
vapor, allow significant hydrogen escape, and oxidize the magma ocean. A third scenario is that Venus had
surface water and habitable conditions early in its history for a short period of time (<1 Gyr), but that a
moist/runaway greenhouse took effect because of a gradually warming Sun, leaving the planet desiccated
ever since. Using a general circulation model, we demonstrate the viability of the first scenario using the
few observational constraints available.We further speculate that large igneous provinces and the global
resurfacing hundreds of millions of years ago played key roles in ending the clement period in its history
and presenting the Venus we see today. The results have implications for what astronomers term “the
habitable zone,” and if Venus-like exoplanets exist with clement conditions akin to modern Earth, we
propose to place them in what we term the “optimistic Venus zone.”
Solar system exploration with space resources - Aiaa asm 2014_bp_9 final paperBryan Palaszewski
Solar System Exploration Augmented by
Lunar and Outer Planet Resource Utilization:
Historical Perspectives and Future Possibilities
Bryan Palaszewski 1
NASA John H. Glenn Research Center
Lewis Field
Cleveland, OH 44135
(216) 977-7493 Voice
(216) 433-5802 FAX
bryan.a.palaszewski@nasa.gov
Fuels and Space Propellants Web Site:
http://www.grc.nasa.gov/WWW/Fuels-And-Space-Propellants/foctopsb.htm
Establishing a lunar presence and creating an industrial capability on the Moon may lead to important new discoveries for all of human kind. Historical studies of lunar exploration, in-situ resource utilization (ISRU) and industrialization all point to the vast resources on the Moon and its links to future human and robotic exploration. In the historical work, a broad range of technological innovations are described and analyzed. These studies depict program planning for future human missions throughout the solar system, lunar launched nuclear rockets, and future human settlements on the Moon, respectively. Updated analyses based on the visions presented are presented. While advanced propulsion systems were proposed in these historical studies, further investigation of nuclear options using high power nuclear thermal propulsion, nuclear surface power, as well as advanced chemical propulsion can significantly enhance these scenarios.
Robotic and human outer planet exploration options are described in many detailed and extensive studies. Nuclear propulsion options for fast trips to the outer planets are discussed. To refuel such vehicles, atmospheric mining in the outer solar system has also been investigated as a means of fuel production for high energy propulsion and power. Fusion fuels such as Helium 3 (3He) and hydrogen can be wrested from the atmospheres of Uranus and Neptune and either returned to Earth or used in-situ for energy production. Helium 3 and hydrogen (deuterium, etc.) were the primary gases of interest with hydrogen being the primary propellant for nuclear thermal solid core and gas core rocket-based atmospheric flight. A series of analyses have investigated resource capturing aspects of atmospheric mining in the outer solar system. These analyses included the gas capturing rate, storage options, and different methods of direct use of the captured gases. While capturing 3He, large amounts of hydrogen and 4He are produced. With these two additional gases, the potential for fueling small and large fleets of additional exploration and exploitation vehicles exists.
The habitability of Proxima Centauri b - I. Irradiation, rotation and volatil...Sérgio Sacani
Proxima b is a planet with a minimum mass of 1.3 M⊕ orbiting within the habitable zone (HZ) of Proxima Centauri, a very low-mass,
active star and the Sun’s closest neighbor. Here we investigate a number of factors related to the potential habitability of Proxima b
and its ability to maintain liquid water on its surface. We set the stage by estimating the current high-energy irradiance of the planet
and show that the planet currently receives 30 times more EUV radiation than Earth and 250 times more X-rays. We compute the time
evolution of the star’s spectrum, which is essential for modeling the flux received over Proxima b’s lifetime. We also show that Proxima
b’s obliquity is likely null and its spin is either synchronous or in a 3:2 spin-orbit resonance, depending on the planet’s eccentricity and
level of triaxiality. Next we consider the evolution of Proxima b’s water inventory. We use our spectral energy distribution to compute
the hydrogen loss from the planet with an improved energy-limited escape formalism. Despite the high level of stellar activity we find
that Proxima b is likely to have lost less than an Earth ocean’s worth of hydrogen (EOH) before it reached the HZ 100–200 Myr after
its formation. The largest uncertainty in our work is the initial water budget, which is not constrained by planet formation models. We
conclude that Proxima b is a viable candidate habitable planet.
Astronomy - State of the Art is a course covering the hottest topics in astronomy. In this section, the Solar System is explored, including place where biology might exist.
Microbial habitability of Europa sustained by radioactive sources Sérgio Sacani
There is an increasing interest in the icy moons of the Solar System due to their potential habitability and as targets for future exploratory missions, which include astrobiological goals. Several studies have reported new results describing the details of these moons’ geological settings; however, there is still a lack of information regarding the deep subsurface environment of the moons. The purpose of this article is to evaluate the microbial habitability of Europa constrained by terrestrial analogue environments and sustained by radioactive energy provided by natural unstable isotopes. The geological scenarios are based on known deep environments on Earth, and the bacterial ecosystem is based on a sulfatereducing bacterial ecosystem found 2.8 km below the surface in a basin in South Africa. The results show the possibility of maintaining the modeled ecosystem based on the proposed scenarios and provides directions for future models and exploration missions for a more complete evaluation of the habitability of Europa and of icy moons in general.
The Carbon Cycle 3 points possible Content Criteria Weight.docxmehek4
The Carbon Cycle
3 points possible
Content Criteria
Weight
The student explains the major pathways and storage reservoirs of the carbon cycle.
0.75
The student discusses how human activities may alter the cycle and the repercussions of these alterations.
0.75
The student responds to at least two classmates’ initial posts by Day 7.
0.5
Research Criteria
The student utilizes at least two scholarly sources in addition to the text.
0.75
Style Criteria
The student utilizes APA format, provides a posting of at least 250 words, and answers with correct spelling and grammar.
0.25
Required Resources
Text
· Botkin, D. B., & Keller, E. A. (2014). Environmental science: Earth as a living planet (9th ed.). Hoboken, NJ: John Wiley & Sons, Inc.
· Chapter 7: The Biochemical Cycles
Article
· Baisre, J. A. (2006). Assessment of nitrogen flows into the Cuban landscape. Biochemistry, 79, 91-108. doi: 10.1007/s10533-006-9004-z
CHAPTER 7
· Botkin, D. B., & Keller, E. A. (2014). Environmental science: Earth as a living planet (9th ed.). Hoboken, NJ: John Wiley & Sons, Inc.
· Chapter 7: The Biochemical Cycles
7.1 Earth, Life, and Chemistry
Earth is a Peculiar Planet
Our planet, Earth, is unique, at least to the extent that we have explored the cosmos. In our solar system and in the Milky Way galaxy, to the extent that we have observed it, Earth is the only body that has the combination of four characteristics: liquid water, water at its triple point (gas, liquid, and solid phases at the same time), plate tectonics, and life. Recent space probes to the moons of Jupiter and Saturn suggest that there may be liquid water on a few of these and perhaps also an equivalent of plate tectonics. And recent studies of Mars suggest that liquid water has broken through to the surface on occasion in the past, causing Earthlike water erosion. In August 2012 the U.S. National Aeronautics and Space Administration (NASA) successfully landed the rover Curiosity on Mars. The fo- cus of the mission is on the chemistry and geology of the planet. The rover is about the size of a small sports car (Figure 7.2). Nuclear-powered, Curiosity is a mobile science laboratory. Scientists are hopeful that chemical tests will provide clues about the possibility of past life on Mars.
The above discussion leads to consideration of the his- tory of Earth over billions of years. This study has prompt- ed some geologists to propose “big history”—to link contemporary history with geologic history, perhaps even going back all the way to the Big Bang 13.8 billion years ago, when our universe was born.2, 3 The main regimes of big history include cosmos, Earth, and life. To these in the context of environmental science, we add human history.2,
Space Travelers and Our Solar System
Life changes the cycling of chemical elements on Earth and has done so for several billions of years.4 When beginning to examine this intriguing effect of life at a global level, it is useful to imagine how tra ...
Venus and Earth have remarkably diferent
surface conditions, yet the lithospheric
thickness and heat fow on Venus may be
Earth-like. This fnding supports a tectonic
regime with limited surface mobility and
dominated by intrusive magmatism.
Radial velocity monitoring has found the signature of a Msin i = 1:3 M planet located within the Habitable Zone of Proxima
Centauri, the Sun’s closest neighbor (Anglada-Escudé et al. 2016). Despite a hotter past and an active host star the planet Proxima b
could have retained enough volatiles to sustain surface habitability (Ribas et al. 2016). Here we use a 3D Global Climate Model (GCM)
to simulate Proxima b’s atmosphere and water cycle for its two likely rotation modes (the 1:1 and 3:2 spin-orbit resonances) while
varying the unconstrained surface water inventory and atmospheric greenhouse eect (represented here with a CO2-N2 atmosphere.)
We find that a broad range of atmospheric compositions can allow surface liquid water. On a tidally-locked planet with a surface water
inventory larger than 0.6 Earth ocean, liquid water is always present (assuming 1 bar of N2), at least in the substellar region. Liquid
water covers the whole planet for CO2 partial pressures & 1 bar. For smaller water inventories, water can be trapped on the night side,
forming either glaciers or lakes, depending on the amount of greenhouse gases. With a non-synchronous rotation, a minimum CO2
pressure of 10 mbar (assuming 1 bar of N2) is required to avoid falling into a completely frozen snowball state if water is abundant.
If the planet is dryer, 0.5 bar of CO2 would suce to prevent the trapping of any arbitrary small water inventory into polar ice
caps. More generally, any low-obliquity planet within the classical habitable zone of its star should be in one of the climate regimes
discussed here.
We use our GCM to produce reflection/emission spectra and phase curves for the dierent rotations and surface volatile inventories.
We find that atmospheric characterization will be possible by direct imaging with forthcoming large telescopes thanks to an angular
separation of 7=D at 1 m (with the E-ELT) and a contrast of 10 7. The magnitude of the planet will allow for high-resolution
spectroscopy and the search for molecular signatures, including H2O, O2, and CO2.
The observation of thermal phase curves, although challenging, can be attempted with JWST, thanks to a contrast of 210 5 at 10 m.
Proxima b will also be an exceptional target for future IR interferometers. Within a decade it will be possible to image Proxima b and
possibly determine whether this exoplanet’s surface is habitable.
Pesquisa mostra que as exoluas podem ser os corpos mais comuns no universo onde se pode encontrar vida. As exoluar aumentam o número de corpos presentes na chamada zona habitável dos exoplanetas.
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Pages 18 -191.4 Earth as a SystemThe Earth System The Earth sy.docxbunyansaturnina
Pages 18 -19
1.4 Earth as a System
The Earth System The Earth system has a nearly endless array of subsystems in which matter is recycled over and over. One familiar loop or subsystem is the hydrologic cycle. It represents the unending circulation of Earth’s water among the hydrosphere, atmosphere, biosphere, and geosphere. Water enters the atmosphere through evaporation from Earth’s surface and transpiration from plants. Water vapor condenses in the atmosphere to form clouds, which in turn produce precipitation that falls back to Earth’s surface. Some of the rain that falls onto the land infiltrates (soaks in) to be taken up by plants or become groundwater, and some flows across the surface toward the ocean. Viewed over long time spans, the rocks of the geosphere are constantly forming, changing, and re-forming. The loop that involves the processes by which one rock changes to another is called the rock cycle and will be discussed at some length later in the chapter. The cycles of the Earth system are not independent of one another; to the contrary, these cycles come in contact and interact in many places. The parts of the Earth system are linked so that a change in one part can produce changes in any or all of the other parts. For example, when a volcano erupts, lava from Earth’s interior may flow out at the surface and block a nearby valley. This new obstruction influences the region’s drainage system by creating a lake or causing streams to change course. The large quantities of volcanic ash and gases that can be emitted during an eruption might be blown high into the atmosphere and influence the amount of solar energy that can reach Earth’s surface. The result could be a drop in air temperatures over the entire hemisphere. Where the surface is covered by lava flows or a thick layer of volcanic ash, existing soils are buried. This causes soil-forming processes to begin anew to transform the new surface material into soil (Figure 1.16). The soil that eventually forms will reflect the interactions among many parts of the Earth system—the volcanic parent material, the climate, and the impact of biological activity. Of course, there would also be significant changes in the biosphere. Some organisms and their habitats would be eliminated by the lava and ash, whereas new settings for life, such as a lake formed by a lava dam, would be created. The potential climate change could also impact sensitive life-forms. The Earth system is characterized by processes that vary on spatial scales from fractions of millimeters to thousands of kilometers. Time scales for Earth’s processes range from seconds to billions of years. As we learn about Earth, it becomes increasingly clear that despite significant separations in distance or time, many processes are connected, and a change in one component can influence the entire system. The Earth system is powered by energy from two sources. The Sun drives external processes that occur in the atmosphere, in the hy.
The divergent fates of primitive hydrospheric water on Earth and MarsSérgio Sacani
Despite active transport into Earth’s mantle, water has been
present on our planet’s surface for most of geological time1,2
.
Yet water disappeared from the Martian surface soon after its
formation. Although some of the water on Mars was lost to space
via photolysis following the collapse of the planet’s magnetic field3–5,
the widespread serpentinization of Martian crust6,7
suggests that
metamorphic hydration reactions played a critical part in the
sequestration of the crust. Here we quantify the relative volumes
of water that could be removed from each planet’s surface via the
burial and metamorphism of hydrated mafic crusts, and calculate
mineral transition-induced bulk-density changes at conditions
of elevated pressure and temperature for each. The metamorphic
mineral assemblages in relatively FeO-rich Martian lavas can
hold about 25 per cent more structurally bound water than those
in metamorphosed terrestrial basalts, and can retain it at greater
depths within Mars. Our calculations suggest that in excess of
9 per cent by volume of the Martian mantle may contain hydrous
mineral species as a consequence of surface reactions, compared to
about 4 per cent by volume of Earth’s mantle. Furthermore, neither
primitive nor evolved hydrated Martian crust show noticeably
different bulk densities compared to their anhydrous equivalents,
in contrast to hydrous mafic terrestrial crust, which transforms
to denser eclogite upon dehydration. This would have allowed
efficient overplating and burial of early Martian crust in a stagnantlid
tectonic regime, in which the lithosphere comprised a single
tectonic plate, with only the warmer, lower crust involved in mantle
convection. This provided an important sink for hydrospheric water
and a mechanism for oxidizing the Martian mantle. Conversely,
relatively buoyant mafic crust and hotter geothermal gradients on
Earth reduced the potential for upper-mantle hydration early in
its geological history, leading to water being retained close to its
surface, and thus creating conditions conducive for the evolution
of complex multicellular life
Predictions of the_atmospheric_composition_of_gj_1132_bSérgio Sacani
GJ 1132 b is a nearby Earth-sized exoplanet transiting an M dwarf, and is amongst the most highly
characterizable small exoplanets currently known. In this paper we study the interaction of a magma
ocean with a water-rich atmosphere on GJ 1132b and determine that it must have begun with more
than 5 wt% initial water in order to still retain a water-based atmosphere. We also determine the
amount of O2
that can build up in the atmosphere as a result of hydrogen dissociation and loss.
We find that the magma ocean absorbs at most ∼ 10% of the O2 produced, whereas more than
90% is lost to space through hydrodynamic drag. The most common outcome for GJ 1132 b from our
simulations is a tenuous atmosphere dominated by O2
, although for very large initial water abundances
atmospheres with several thousands of bars of O2
are possible. A substantial steam envelope would
indicate either the existence of an earlier H2
envelope or low XUV flux over the system’s lifetime. A
steam atmosphere would also imply the continued existence of a magma ocean on GJ 1132 b. Further
modeling is needed to study the evolution of CO2
or N2
-rich atmospheres on GJ 1132 b.
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
A tale of scale & speed: How the US Navy is enabling software delivery from l...sonjaschweigert1
Rapid and secure feature delivery is a goal across every application team and every branch of the DoD. The Navy’s DevSecOps platform, Party Barge, has achieved:
- Reduction in onboarding time from 5 weeks to 1 day
- Improved developer experience and productivity through actionable findings and reduction of false positives
- Maintenance of superior security standards and inherent policy enforcement with Authorization to Operate (ATO)
Development teams can ship efficiently and ensure applications are cyber ready for Navy Authorizing Officials (AOs). In this webinar, Sigma Defense and Anchore will give attendees a look behind the scenes and demo secure pipeline automation and security artifacts that speed up application ATO and time to production.
We will cover:
- How to remove silos in DevSecOps
- How to build efficient development pipeline roles and component templates
- How to deliver security artifacts that matter for ATO’s (SBOMs, vulnerability reports, and policy evidence)
- How to streamline operations with automated policy checks on container images
Smart TV Buyer Insights Survey 2024 by 91mobiles.pdf91mobiles
91mobiles recently conducted a Smart TV Buyer Insights Survey in which we asked over 3,000 respondents about the TV they own, aspects they look at on a new TV, and their TV buying preferences.
UiPath Test Automation using UiPath Test Suite series, part 4DianaGray10
Welcome to UiPath Test Automation using UiPath Test Suite series part 4. In this session, we will cover Test Manager overview along with SAP heatmap.
The UiPath Test Manager overview with SAP heatmap webinar offers a concise yet comprehensive exploration of the role of a Test Manager within SAP environments, coupled with the utilization of heatmaps for effective testing strategies.
Participants will gain insights into the responsibilities, challenges, and best practices associated with test management in SAP projects. Additionally, the webinar delves into the significance of heatmaps as a visual aid for identifying testing priorities, areas of risk, and resource allocation within SAP landscapes. Through this session, attendees can expect to enhance their understanding of test management principles while learning practical approaches to optimize testing processes in SAP environments using heatmap visualization techniques
What will you get from this session?
1. Insights into SAP testing best practices
2. Heatmap utilization for testing
3. Optimization of testing processes
4. Demo
Topics covered:
Execution from the test manager
Orchestrator execution result
Defect reporting
SAP heatmap example with demo
Speaker:
Deepak Rai, Automation Practice Lead, Boundaryless Group and UiPath MVP
Unlocking Productivity: Leveraging the Potential of Copilot in Microsoft 365, a presentation by Christoforos Vlachos, Senior Solutions Manager – Modern Workplace, Uni Systems
Transcript: Selling digital books in 2024: Insights from industry leaders - T...BookNet Canada
The publishing industry has been selling digital audiobooks and ebooks for over a decade and has found its groove. What’s changed? What has stayed the same? Where do we go from here? Join a group of leading sales peers from across the industry for a conversation about the lessons learned since the popularization of digital books, best practices, digital book supply chain management, and more.
Link to video recording: https://bnctechforum.ca/sessions/selling-digital-books-in-2024-insights-from-industry-leaders/
Presented by BookNet Canada on May 28, 2024, with support from the Department of Canadian Heritage.
Elevating Tactical DDD Patterns Through Object CalisthenicsDorra BARTAGUIZ
After immersing yourself in the blue book and its red counterpart, attending DDD-focused conferences, and applying tactical patterns, you're left with a crucial question: How do I ensure my design is effective? Tactical patterns within Domain-Driven Design (DDD) serve as guiding principles for creating clear and manageable domain models. However, achieving success with these patterns requires additional guidance. Interestingly, we've observed that a set of constraints initially designed for training purposes remarkably aligns with effective pattern implementation, offering a more ‘mechanical’ approach. Let's explore together how Object Calisthenics can elevate the design of your tactical DDD patterns, offering concrete help for those venturing into DDD for the first time!
Climate Impact of Software Testing at Nordic Testing DaysKari Kakkonen
My slides at Nordic Testing Days 6.6.2024
Climate impact / sustainability of software testing discussed on the talk. ICT and testing must carry their part of global responsibility to help with the climat warming. We can minimize the carbon footprint but we can also have a carbon handprint, a positive impact on the climate. Quality characteristics can be added with sustainability, and then measured continuously. Test environments can be used less, and in smaller scale and on demand. Test techniques can be used in optimizing or minimizing number of tests. Test automation can be used to speed up testing.
DevOps and Testing slides at DASA ConnectKari Kakkonen
My and Rik Marselis slides at 30.5.2024 DASA Connect conference. We discuss about what is testing, then what is agile testing and finally what is Testing in DevOps. Finally we had lovely workshop with the participants trying to find out different ways to think about quality and testing in different parts of the DevOps infinity loop.
PHP Frameworks: I want to break free (IPC Berlin 2024)Ralf Eggert
In this presentation, we examine the challenges and limitations of relying too heavily on PHP frameworks in web development. We discuss the history of PHP and its frameworks to understand how this dependence has evolved. The focus will be on providing concrete tips and strategies to reduce reliance on these frameworks, based on real-world examples and practical considerations. The goal is to equip developers with the skills and knowledge to create more flexible and future-proof web applications. We'll explore the importance of maintaining autonomy in a rapidly changing tech landscape and how to make informed decisions in PHP development.
This talk is aimed at encouraging a more independent approach to using PHP frameworks, moving towards a more flexible and future-proof approach to PHP development.
Removing Uninteresting Bytes in Software FuzzingAftab Hussain
Imagine a world where software fuzzing, the process of mutating bytes in test seeds to uncover hidden and erroneous program behaviors, becomes faster and more effective. A lot depends on the initial seeds, which can significantly dictate the trajectory of a fuzzing campaign, particularly in terms of how long it takes to uncover interesting behaviour in your code. We introduce DIAR, a technique designed to speedup fuzzing campaigns by pinpointing and eliminating those uninteresting bytes in the seeds. Picture this: instead of wasting valuable resources on meaningless mutations in large, bloated seeds, DIAR removes the unnecessary bytes, streamlining the entire process.
In this work, we equipped AFL, a popular fuzzer, with DIAR and examined two critical Linux libraries -- Libxml's xmllint, a tool for parsing xml documents, and Binutil's readelf, an essential debugging and security analysis command-line tool used to display detailed information about ELF (Executable and Linkable Format). Our preliminary results show that AFL+DIAR does not only discover new paths more quickly but also achieves higher coverage overall. This work thus showcases how starting with lean and optimized seeds can lead to faster, more comprehensive fuzzing campaigns -- and DIAR helps you find such seeds.
- These are slides of the talk given at IEEE International Conference on Software Testing Verification and Validation Workshop, ICSTW 2022.
Essentials of Automations: The Art of Triggers and Actions in FMESafe Software
In this second installment of our Essentials of Automations webinar series, we’ll explore the landscape of triggers and actions, guiding you through the nuances of authoring and adapting workspaces for seamless automations. Gain an understanding of the full spectrum of triggers and actions available in FME, empowering you to enhance your workspaces for efficient automation.
We’ll kick things off by showcasing the most commonly used event-based triggers, introducing you to various automation workflows like manual triggers, schedules, directory watchers, and more. Plus, see how these elements play out in real scenarios.
Whether you’re tweaking your current setup or building from the ground up, this session will arm you with the tools and insights needed to transform your FME usage into a powerhouse of productivity. Join us to discover effective strategies that simplify complex processes, enhancing your productivity and transforming your data management practices with FME. Let’s turn complexity into clarity and make your workspaces work wonders!
Alt. GDG Cloud Southlake #33: Boule & Rebala: Effective AppSec in SDLC using ...James Anderson
Effective Application Security in Software Delivery lifecycle using Deployment Firewall and DBOM
The modern software delivery process (or the CI/CD process) includes many tools, distributed teams, open-source code, and cloud platforms. Constant focus on speed to release software to market, along with the traditional slow and manual security checks has caused gaps in continuous security as an important piece in the software supply chain. Today organizations feel more susceptible to external and internal cyber threats due to the vast attack surface in their applications supply chain and the lack of end-to-end governance and risk management.
The software team must secure its software delivery process to avoid vulnerability and security breaches. This needs to be achieved with existing tool chains and without extensive rework of the delivery processes. This talk will present strategies and techniques for providing visibility into the true risk of the existing vulnerabilities, preventing the introduction of security issues in the software, resolving vulnerabilities in production environments quickly, and capturing the deployment bill of materials (DBOM).
Speakers:
Bob Boule
Robert Boule is a technology enthusiast with PASSION for technology and making things work along with a knack for helping others understand how things work. He comes with around 20 years of solution engineering experience in application security, software continuous delivery, and SaaS platforms. He is known for his dynamic presentations in CI/CD and application security integrated in software delivery lifecycle.
Gopinath Rebala
Gopinath Rebala is the CTO of OpsMx, where he has overall responsibility for the machine learning and data processing architectures for Secure Software Delivery. Gopi also has a strong connection with our customers, leading design and architecture for strategic implementations. Gopi is a frequent speaker and well-known leader in continuous delivery and integrating security into software delivery.
The Art of the Pitch: WordPress Relationships and SalesLaura Byrne
Clients don’t know what they don’t know. What web solutions are right for them? How does WordPress come into the picture? How do you make sure you understand scope and timeline? What do you do if sometime changes?
All these questions and more will be explored as we talk about matching clients’ needs with what your agency offers without pulling teeth or pulling your hair out. Practical tips, and strategies for successful relationship building that leads to closing the deal.
FIDO Alliance Osaka Seminar: The WebAuthn API and Discoverable Credentials.pdf
Exoplanet habitability
1. DOI: 10.1126/science.1232226
, 577 (2013);340Science
Sara Seager
Exoplanet Habitability
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2. REVIEW
Exoplanet Habitability
Sara Seager
The search for exoplanets includes the promise to eventually find and identify habitable worlds. The
thousands of known exoplanets and planet candidates are extremely diverse in terms of their masses
or sizes, orbits, and host star type. The diversity extends to new kinds of planets, which are very
common yet have no solar system counterparts. Even with the requirement that a planet’s surface
temperature must be compatible with liquid water (because all life on Earth requires liquid water),
a new emerging view is that planets very different from Earth may have the right conditions for life.
The broadened possibilities will increase the future chances of discovering an inhabited world.
F
or thousands of years people have won-
dered, “Are we alone?” Now, for the first
time in human history, the answer to this
and other long-standing questions
in the search for life beyond our
solar system may finally be in
reach through the observation and
study of exoplanets—planets or-
biting stars other than the Sun.
The research field of exoplanets
has grown dramatically since the
first planet orbiting a Sun-like star
was discovered nearly 20 years ago
(1). Nearly 1000 exoplanets are
known to orbit nearby stars, a few
thousand more planet “candidates”
have been identified, and planets
are so common that on average
every star in the Milky Way should
have at least one planet (2, 3). The
numbers of exoplanet candidates
found by NASA’s Kepler space
telescope are high enough that ro-
bust statements of the frequency
of their occurrence is possible, in-
cluding the astonishing finding that
small planets by far outnumber
large planets in our galaxy (3, 4),
and the first statement about how
common Earth-size planets are
in the habitable zones of small
stars (5).
The habitable zone is a region
around a star where a planet can
have surface temperatures con-
sistent with the presence of liq-
uid water. All life on Earth requires
liquid water, so the planetarysurface-
temperature requirement appears
to be a natural one. The climates
of planets with thin atmospheres are dominated
by external energy input from the host star, so
that a star’s “habitable zone” is based on dis-
tance from the host star. Small stars have a hab-
itable zone much closer to them as compared to
Sun-like stars, owing to their lower luminosity.
The habitable zone was first discussed in the
mid-20th century, inspired by attempts to under-
stand the climate of early Earth and Mars (6, 7),
and was later brought onto a self-consistent foot-
ing when the carbonate-silicate cycle was pro-
posed as a climate-stabilizing mechanism (8, 9).
The habitable zone for exoplanets was first
presented and modeled in detail by (9), who also
suggested an empirical version based on the
concept that both Venus [0.7 astronomical units
(AU) from the Sun, where an AU is the Earth-
Sun distance] and Mars (1.5 AU) may have had
liquid surface water at some point in the past.
Most exoplanet habitable-zone research that fol-
lowed continued to focus on terrestrial-like planet
atmospheres orbiting main-sequence stars [see (10)
and references therein]. This article reviews up-
dates to the habitable zone and their rationale.
A planet in the habitable zone has no guar-
antee of actually being habitable. Venus and
Earth may both be argued as being in the Sun’s
habitable zone and would appear from exoplanet
discovery techniques to be the same size and
mass. Yet, Venus is completely hostile to life
owing to a strong greenhouse effect and resulting
high surface temperatures (>700 K),
whereas Earth has the right sur-
face temperature for liquid water
oceans and is teeming with life.
If there is one important lesson
from exoplanets, it is that any-
thing is possible within the laws
of physics and chemistry. Planets
of almost all masses, sizes, and
orbits have been detected (Fig. 1),
illustrating not only the stochastic
nature of planet formation but also
a subsequent migration through
the planetary disk from the planet’s
place of origin [e.g., (11)]. The
huge diversity of exoplanets and
the related anticipated variation
in their atmospheres, in terms of
mass and composition, have mo-
tivated a strong desire to revise
the view of planetary habitability.
In parallel, there is a growing ac-
ceptance that even in the future,
the number of suitable planets ac-
cessible to detailed follow-up ob-
servations may be very small. To
maximize our chances of identify-
ing a habitable world, a broader
understanding of which planets are
habitable is a necessity.
Habitable Planets,
Conventionally Defined
The conventionally habitable planet
is one with surface liquid water.
Water is required for all life as we
know it, and has motivated a man-
tra in astrobiology, “follow the water.” Challenging
the water requirement paradigm, a National Acad-
emies report (12) concluded that although a liq-
uid environment is required by life, it need not be
limited to water. In the search for life beyond the
solar system, however, we still focus on environ-
ments that support liquid water simply because
Department of Earth, Atmospheric, and Planetary Sciences,
Massachusetts Institute of Technology, Cambridge, MA 02139,
USA.
E-mail: seager@mit.edu
Semimajor axis (AU)
Earthmasses
10–2
104
103
102
101
100
10–1
10–2
10–1
100
101
Timing
Radial velocity
Transit
Microlensing
Direct imaging
102
103
U N
S
13MJup
JJ
EV
Ma
M
Fig. 1. Known exoplanets as of March 2013. Exoplanets are found at a nearly
continuous range of masses and semimajor axes. Many different techniques are
successful at discovering exoplanets, as indicated by the different symbols. The
solar system planets are denoted by the first one or two letters of their name.
The horizontal line is the conventional upper limit to a planet mass, 13 Jupiter
masses. The sloped, lower boundary to the collection of gray squares is due to a
selection effect in the radial velocity technique. Small planets are beneath the
threshold for the current state of almost all exoplanet detection techniques. Data
are from http://exoplanet.eu/.
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3. water is the most accessible, abundant, and com-
mon liquid in terms of planetary material (13).
For illustration and review, we consider water
on the terrestrial planets in our own solar system.
Earth is touted as the “Goldilocks planet”—not
too hot, not too cold, but just right for surface li-
quid water (14). Venus, 30% closer to the Sun than
Earth and receiving 90% more radiation from the
Sun, may have had liquid water oceans billions
of years ago, as possibly implied by the elevated
deuterium/hydrogen (D/H) ratio in the venusian
atmosphere (15). Because of warm surface temper-
atures, water evaporated to saturate the upper at-
mosphere where solar extreme ultraviolet (EUV)
radiation photodissociated the H2O, enabling H
to escape to space. The increasing atmospheric wa-
ter vapor further warmed the surface, creating a
positive feedback loop that led to a “runaway green-
house effect,” which caused Venus to rapidly lose
its oceans [but compare (16)]. Mars, at 1.5 AU
from the Sun, is thought to have had at least epi-
sodic surface liquid water in the past, based pre-
dominantly on geomorphological features [e.g.,
(17)]. Mars was too small to hold onto a warming
atmosphere and is now so cold there is no place
on the Martian surface where water could be liquid.
The habitable zone for terrestrial-type exoplanets
with terrestrial-like atmospheres of various masses
and CO2 concentration are described in (10) and
result in a habitable zone of 0.99 to 1.7 AU (Fig. 2).
The inner edge of the habitable zone is determined
by loss of water via the runaway greenhouse ef-
fect (18) and the outer edge by CO2 condensation.
For exoplanets, we cannot directly observe liq-
uid surface water (19). Atmospheric water vapor
may be used as a proxy; as long as a temperate
planet is small or of low enough mass, water va-
por should not be present because water will be
photodissociated with H escaping to space. At-
mospheric water vapor has been detected on hot
giant transiting exoplanets [e.g., (20)] and is high-
ly sought after for the mini Neptune GJ 1214b [e.g.,
(21)]. Both of these types of planets are too hot
for surface liquid water [for a discussion of
GJ 1214b, see (22)]; notably, water vapor will be
naturally occurring on planets that are massive
enough or cold enough to hold on to water vapor
molecules. The detection of water vapor in the
atmosphere of smaller, more terrestrial-like planets
is currently out of reach.
Given the observational inaccessibility of
the key habitability indicator water vapor on
terrestrial-like exoplanets, the habitable zone
around a star is a powerful guide for astronomers
because it tells us where to focus future efforts
of exoplanet discovery. We must redefine the
habitable-zone concept, however, given the ex-
pected and observed diversity of exoplanets.
The Diversity of Exoplanets and the Controlling
Factors of Habitability
Taking surface liquid water as a requirement,
what types of planets are habitable? Water is in
the liquid phase for a range of temperatures and
pressures. Planets should also have a wide range
of surface temperatures and pressures, expected
from their diversity in mass and size and likely
atmospheres. If we could connect the liquid
water phase diagram with planet surface con-
ditions, broadly speaking, we would know to
first order which planets may be habitable.
The water phase diagram can be used as a
qualitative guide to show that pressures thousands
of times higher than Earth’s 1-bar surface pressure
can maintain liquid water at high temperatures
(23). A suitable temperature for life can be con-
sidered to be between the freezing point of water
and the upper temperature limits for life, about
395 K (24). A notable inaccuracy in the phase
diagram is that the water phase boundaries at
high pressures have not been studied for a variety
of gas mixtures relevant for exoplanets (25).
The surface temperature on an exoplanet is
governed by the atmosphere’s greenhouse gases
(or lack thereof ). Specifically, the greenhouse
gases absorb and reradiate energy from the host
star, in the form of upwelling infrared (IR) radi-
ation from the planet’s surface. Whereas on Earth
we are concerned with, e.g., parts-per-million rise
in the greenhouse gas CO2 concentrations, for
potentially habitable exoplanets we do not know
a priori and cannot yet measure what gases are
in the atmosphere even to the tens of percent lev-
el. The atmospheric mass and composition of any
specific small exoplanet is not predictable (26).
Nevertheless, it is worth summarizing some
key factors controlling a planet atmosphere’s
greenhouse gas inventory. A planet’s atmosphere
forms from outgassing during planet formation or
is gravitationally captured from the surrounding
proto-planetary nebula. For terrestrial planets, the
primordial atmosphere may be completely changed
by escape of light gases to space, continuous
outgassing from an active young interior, and
bombardment by asteroids and comets. At a later
stage, the physical processes operating at the
top or bottom of the atmosphere still sculpt the
atmosphere. These physical processes are well
studied by exoplanet theorists but often with con-
troversy or no conclusion. For example, atmo-
spheric escape is induced by the host star’s EUV
flux and carried out by a number of thermal or
nonthermal escape mechanisms. But the star’s
past EUV flux, which of the escape mechanisms
was at play, and whether or not the planet has a
protective magnetic field are not known [e.g.,
(27)]. As a second example, at the bottom of
the atmosphere, plate tectonics and volcanic out-
gassing contribute to burial and recycling of at-
mospheric gases, but arguments as to whether
or not plate tectonics will occur in a super-Earth
planet more massive than Earth are still under
debate (28, 29). A long list of other surface and
interior processes affect the atmospheric com-
position, including but not limited to the ocean
fraction for dissolution of CO2 and for atmo-
spheric relative humidity, redox state of the plan-
etary surface and interior, acidity levels of the
oceans planetary albedo, and surface gravity [for
MassofstarrelativetoSun
Radius of orbit relative to Earth’s
0
0.2
1
2
0.1 1 10 100
I N T E R N A L
H E A T
R E Q U I R E D
Earth
Star
type
Dry
terrestrial
planet
Earth-like
planet
Hydrogen-
atmosphere
planet
Radial velocity
Transit
Microlensing
Fig. 2. The habitable zone. The light blue region depicts the “conventional” habitable zone for
planets with N2-CO2-H2O atmospheres (9, 10). The yellow region shows the habitable zone as extended
inward for dry planets (36, 37), as dry as 1% relative humidity (37). The outer darker blue region shows
the outer extension of the habitable zone for hydrogen-rich atmospheres (34) and can extend even out
to free-floating planets with no host star (35). The solar system planets are shown with images. Known
exoplanets are shown with symbols [here, planets with a mass or minimum mass less than 10 Earth
masses or a radius less than 2.5 Earth radii taken from (66)].
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4. a more detailed list, see (30)]. Many other factors
are relevant to habitability, including the radiation
environment from the star, especially the energy
distribution as a function of wavelength and the
EUV radiation that destroys molecules and deter-
mines their atmospheric lifetime, and x-ray fluxes
that could be detrimental to surface life (27). In
some cases, planets have been found to orbit one
or both stars of a binary star system, complicating
the influence of stellar radiation.
A Major Extension of the Habitable Zone
For our qualitative assessment of habitability, we
therefore focus on the dominant planetary atmo-
spheric greenhouse gases and how
they delimit the habitable zone (Fig. 2).
The most important atmospher-
ic greenhouse gas that extends the
habitable zone to large planet-star
separation is molecular hydrogen
(H2). Planets are expected to form
with some primordial light gases,
either H2 (from interior outgassing)
(26, 31) or H2 and He (from grav-
itational capture of gas from the
surrounding protoplanetary disk).
Although small planets like Earth,
Venus, and Mars are unable to re-
tain these light gases, more massive
or colder exoplanets are expected
to be able to do so. H2 is a formi-
dable greenhouse gas, because it
can absorb radiation over a wide,
continuous wavelength range. Most
molecules absorb in discreet bands.
As a homonuclear molecule, H2 does
not have a dipole moment and there-
fore lacks the typical rotational-
vibrational bands that absorb light
at near-IR wavelengths. However,
a momentary dipole is induced by
collisions, and thus at high enough
pressures, frequent collisions induce
very broadband absorption (32, 33).
Furthermore, H2 does not condense
until tens of kelvin at 1- to 100-bar
pressures (in comparison, CO2 con-
denses at about 190 to 250 K for 1-
to 10-bar pressures and is therefore
a cutoff for the cold end of conventional planet
habitability). The potency of H2 as a greenhouse
gas means that planets can have surface liquid
water at a factor of several times larger planet-
sun separations than planets with CO2 atmo-
spheres (34) and even possibly extending to
rogue planets that were ejected from their birth
planetary system and are now floating through
the galaxy (35).
The inner edge of the habitable zone is con-
trolled by the strong greenhouse gas H2O, which
is fundamentally unavoidable on habitable worlds.
Surface liquid water—the adopted requirement
for habitability—gives rise to atmospheric water
vapor. The habitable planets closest to their host
stars must therefore be relatively dry (36, 37)—
that is, with a smaller ocean-land fraction than
Earth—so the atmosphere will have less water
vapor than Earth’s. But the putative inner-edge
habitable-zone planet must not be too dry; other-
wise, CO2 cannot be washed out of the atmo-
sphere, which would lead to a buildup of CO2
and subsequent warming. Theoretical simula-
tions of planet formation indicate that dry planets
are possible [e.g., (38)].
Pockets of small areas of habitability on an
individual exoplanet are usually disregarded for
exoplanets (39); the concern is that they will not
lead to any detectable atmospheric signatures.
Although large planetary moons of giant planets
may be habitable (some might even have interior
energy generated by planet-moon tidal friction),
detectability of the moon’s atmosphere is a con-
cern because of severe contamination from the
adjacent larger, brighter planet.
We have seen that planetary habitability is
very planet-specific. The habitable zone has
been defined with an inner edge of about 0.5 AU
around a solar-like star, for a dry rocky planet
(37), out to 10 AU around a solar-like star for a
planet with an H2 atmosphere and no interior en-
ergy (34), and even possibly out to free-floating
planets with no host star, for planets with thick
H2 atmospheres (35) (Fig. 2).
Ideally, we would triage each planet first by
the planet’s bulk density, using a measured mass
and radius, to screen planets for those that have
thin atmospheres. Next, we could use the star’s
luminosity and planet-star separation, as well
as model possibilities of the planet’s interior, to
assess whether the likely surface temperatures are
conducive to support liquid water. For planets
that pass the tests, telescopic observations of the
planet’s atmosphere to identify water vapor as a
proxy for surface liquid water would be a de-
finitive step for identifying a habitable world.
However, for most exoplanets, such
fundamental measurements will not
be possible. In some cases, a planet’s
mass but not size can be measured;
in other cases, the size but not mass
can be measured, and the atmosphere
will be accessible only for a few
small planets orbiting nearby stars.
Biosignature Gases
The main interest in defining a hab-
itable planet is to identify an inhabited
one, via remote-sensing observations
of biosignature gases. Biosignature
gases are gases produced by life that
accumulate in a planetary atmosphere
to high enough levels for remote de-
tection by futuristic space telescopes.
The underpinning assumption is that
life uses chemical reactions to ex-
tract, store, and release energy, such
that biosignature gases are gener-
ated as by-products somewhere in
life’s metabolic process.
Atmospheric biosignature gases
have been studied theoretically as
indicators of life for nearly half a
century (40, 41), with the proposed
concept that a favorable biosigna-
ture gas is one that is many orders
of magnitude out of thermochem-
ical equilibrium with the planetary
atmosphere.
Not all biosignature gases will
be detectable from afar. Only glob-
ally mixed, spectroscopically active gases will be
visible in an exoplanet spectrum. On Earth, the
dominant global biosignature gases are O2 (and its
photolytic product O3) produced by plants and
photosynthetic bacteria, N2O, and for early Earth
possibly CH4 (42) (Fig. 3).
The microbial world on Earth is incredibly
diverse, and microorganisms produce a broad
range of gases (43). Some of these gases, such as
CO2, are not unique to life as they occur naturally
in the atmosphere. Other biosignature gases may
be negligible on present-day Earth but accumu-
late to relevant levels in an environment substan-
tially different from Earth’s. Some examples that
Wavelength (µm)
logFluxFlux(×10–11)Reflectance
1.0
0.5
0
–10
–9
–8
–7
–6
1.0
0.5
10
1 2 3 4
0.6 0.8 1.0 1.2 1.4
H2O
H2O
H2O
H2O
CO2
CO2
CO2CH4
O3
A
B
C
O3
Ray
O2
1.6
15 20 25
Fig. 3. Earth as an exoplanet, via observed disk-integrated spectra. (A)
Visible-wavelength spectrum from Earthshine measurements plotted as normal-
ized reflectance (67). (B) Near-infrared spectrum from NASA’s EPOXI mission
with flux in units of W m−2
mm−1
(68). (C) Mid-infrared spectrum as observed
by Mars Global Surveyor enroute to Mars with flux in units of W m−2
Hz−1
(69).
Major molecular absorption features are noted, including Rayleigh scatter-
ing. Only Earth’s spectroscopically active, globally mixed gases would be
observable from a remote space telescope.
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5. have been studied for terrestrial-like atmospheres
include organosulfur compounds, particularly
methanethiol(CH3SH,thesulfuranalogofmethanol)
(44); CH3Cl, a hydrogen halide (45); and sulfur
biogenic gases on anoxic planets (46).
A major highlight from the last decade of bio-
signature gas research is the realization that low-
EUV radiation environments, compared to solar
radiation levels, lead to a much higher concentra-
tion of biosignature gases. This is because the
stellar EUV radiation creates the radical OH (in
some cases O), which destroys many gases in the
atmosphere and thus reduces the gas lifetime (45).
In an H2-rich atmosphere, the same result holds
with H as the major reactive species. Low-EUV
radiation environments, compared to solar radiation
levels, are found around inactive M dwarf stars (47).
Many biosignature gases have a “false pos-
itive” interpretation because they can be produced
abiotically. False positives can, it is hoped, be iden-
tified by other atmospheric diagnostics. For exam-
ple, photodissociation of water vapor in a runaway
greenhouse with H escaping to space could lead to
detectable O2 levels. This situation could be iden-
tified by an atmosphere heavily saturated with
water vapor. O2 could also accumulate in a dry,
CO2-rich planet with weak geochemical sinks
for O2, a case that could be identified through
strong CO2 and weak H2O features (48, 49).
A sobering thought usually left unacknowledged
is that when we finally discover biosignature
gases, it may be not with a triumphant 100%
certainty but rather with an assigned probability,
depending on the level at which the false positive
likelihood can be ascertained.
How to Find and Identify a Habitable World
In parallel to developing the theoretical founda-
tion for planetary habitability, astronomers are
developing instruments, telescopes, and space
mission concepts to find and identify habitable or
inhabited worlds. There are two ways to observe
exoplanet atmospheres, and this leads to a “two-
pronged approach.”
The first approach is direct imaging [reviewed
in (50)]. Here, the planet is observed as a point
source (not spatially resolved like the beautiful
Apollo images of Earth), and with the appropriate
instrumentation, the light could be dispersed into
a spectrum. The two objectives are to spatially
separate the planet and star on the sky and to
observe the planet literally within the glare of
the host star. The limiting challenge for a planet
like Earth is not its faintness—a relatively near-
by Earth would not be fainter than the faintest
galaxies ever observed by the Hubble Space
Telescope—but the planet’s proximity to a bright
host. The Sun is 10 billion times as bright as Earth
at visible wavelengths. The low-luminosity M stars
are even more challenging to observe because
of the smaller planet-star angular separation on
the sky for the habitable zone. The use of a space-
based telescope to image these planets is essen-
tial, both to get above the blurring effects of Earth’s
atmosphere and to avoid having to contend with
the presence of these gases in our own atmosphere
during an Earth-based hunt for biosignatures
[compare (51)]. Implementation of the optical
mathematics and engineering for blocking out
starlight for planet finding is a subfield that has
proceeded at a breathtaking pace (50), culminating
in many concepts described under the umbrella
term “Terrestrial Planet Finder” (TPF) (named
after a cancelled set of missions under study by
NASA in the early 2000s; the European Space
Agency had a version called “Darwin”). Although
a spectroscopically capable direct-imaging space
mission to survey the 100 nearest Sun-like stars
is now out of reach owing to an estimated cost
of more than 5 billion dollars, technology devel-
opment is still ongoing (52). A prescient saying
in the exoplanet community Is that “all roads lead
to TPF,” because space-based direct imaging is the
prime way to find and identify a true Earth twin.
The second approach is transit finding [re-
viewed in (53)] and transit spectroscopy. When
a planet goes in front of its host star as seen
from a telescope, some of the starlight will pass
through the planet’s atmosphere, and the atmo-
spheric features will be imprinted on the starlight.
In addition, when the planet goes behind the
star (called “secondary eclipse”), the planet light
will disappear and then reappear. For such tran-
sit and eclipse observations, the planet and star
are not spatially separated on the sky but are instead
observed in the “combined light” of the planet-
star system: Using the starlight as a calibration tool
enables the high-contrast measurements. Atmo-
spheres of dozens of hot Jupiter exoplanets have
been observed in this way. Although the Earth-
Sun analog signal is still too small for observa-
tion, Earth-size and larger planets transiting M stars
are suitable (54). M stars are favorable in many
ways, from detectability to characterization, because
the small star makes relative planet-to-star mea-
surement signals larger than for Sun-like stars (55).
The obstacle to observing transiting planets is
that the required orbital alignment will be fortu-
itous and infrequent, limiting the numbers of
transiting planets accessible for study. The good
news is that for planets orbiting quiet M stars,
biosignature gases will accumulate, and simu-
lations show that several such objects should
exist and will be available for study with the
under-construction James Webb Space Telescope
[e.g., (56)]. First, we need a pool of suitable
transiting planets orbiting quiet M stars (57) and
next, a large amount of telescope time, perhaps
tens of hours or more per planet. This scenario
represents our nearest-term chance of identifying
a habitable world.
Epilogue
Planet habitability is planet specific, even with
the main imposed criterion that surface liquid
water must be present. This is because the huge
range of planet diversity in terms of masses, or-
bits, and star types should extend to planet atmo-
spheres and interiors, based on the stochastic
nature of planet formation and subsequent evo-
lution. The diversity of planetary systems extends
far beyond planets in our solar system. The hab-
itable zone could exist from about 0.5 AU out to
10 AU for a solar-type star, or even beyond, de-
pending on the planet’s interior and atmosphere
characteristics. As such, there is no universal
habitable zone applicable to all exoplanets.
Many questions related to physical processes
that govern the atmosphere, which itself controls
habitability, may remain unanswered owing to a
lack of observables. For example, which planets
have plate tectonics and which have protective
magnetic fields? Either there are no connections
to observables or the observables are too weak for
current and future instrumentation to measure.
Research strides are currently being made with
statistical assessments of the occurrence rate of
different sizes and masses of planets. This sta-
tistical phase of exoplanet research is moving
toward estimates of the frequency of habitable
planets with a handful of habitable-zone candi-
dates tentatively identified. This statistical phase
of exoplanets is expected to continue to flourish
and dominate exoplanet science until the next gen-
eration of ground- and space-based telescopes.
Ultimately, a return to study of compelling
individual objects is required—at any cost—if we
want to assess a planet’s habitability or attain the
goal of identifying signs of life via biosignature
gases. Is there any hope that the next space tele-
scope, the James Webb Space Telescope, could
be the first to provide evidence of biosignature
gases? Yes, if—and only if—every single factor
is in our favor. First, we need to discover a pool
of super-Earths transiting in the “extended” hab-
itable zones of nearby, quiet M stars. Second, life
must not only exist on one of those planets, but
must also produce biosignature gases that are
spectroscopically active. Regardless of the search
for life, the field of exoplanet characterization
is on track to understand habitability and to find
habitable worlds.
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Acknowledgments: I thank A. Zsom, V. Stamenkovic, and
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the figures.
10.1126/science.1232226
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