Planets less massive than about 10 MEarth are expected to have no massive H-He atmosphere and a c... more Planets less massive than about 10 MEarth are expected to have no massive H-He atmosphere and a cometary composition (50% rocks, 50% water, by mass) provided they formed beyond the snowline of protoplanetary disks. Due to inward migration, such planets could be found at any distance between their formation site and the star. If migration stops within the habitable zone, this will produce a new kind of planets, called Ocean-Planets. Ocean-planets typically consist in a silicate core, surrounded by a thick ice mantle, itself covered by a 100 km deep ocean. The existence of ocean-planets raises important astrobiological questions: Can life originate on such body, in the absence of continent and ocean-silicate interfaces? What would be the nature of the atmosphere and the geochemical cycles ? In this work, we address the fate of Hot Ocean-Planets produced when migration ends at a closer distance. In this case the liquid/gas interface can disappear, and the hot H2O envelope is made of a ...
One aim of modern astronomy is to detect temperate, Earth-like exoplanets that are well suited fo... more One aim of modern astronomy is to detect temperate, Earth-like exoplanets that are well suited for atmospheric characterization. Recently, three Earth-sized planets were detected that transit (that is, pass in front of) a star with a mass just eight per cent that of the Sun, located 12 parsecs away. The transiting configuration of these planets, combined with the Jupiter-like size of their host star-named TRAPPIST-1-makes possible in-depth studies of their atmospheric properties with present-day and future astronomical facilities. Here we report the results of a photometric monitoring campaign of that star from the ground and space. Our observations reveal that at least seven planets with sizes and masses similar to those of Earth revolve around TRAPPIST-1. The six inner planets form a near-resonant chain, such that their orbital periods (1.51, 2.42, 4.04, 6.06, 9.1 and 12.35 days) are near-ratios of small integers. This architecture suggests that the planets formed farther from the...
The discovery of almost two thousand exoplanets has revealed an unexpectedly diverse planet popul... more The discovery of almost two thousand exoplanets has revealed an unexpectedly diverse planet population. We see gas giants in few-day orbits, whole multi-planet systems within the orbit of Mercury, and new populations of planets with masses between that of the Earth and Neptune-all unknown in the Solar System. Observations to date have shown that our Solar System is certainly not representative of the general population of planets in our Milky Way. The key science questions that urgently need addressing are therefore: What are exoplanets made of? Why are planets as they are? How do planetary systems work and what causes the exceptional diversity observed as compared to the Solar System? The EChO (Exoplanet Characterisation Observatory) space mission was conceived to take up the challenge to explain this diversity in terms of formation, evolution, internal structure and planet and atmospheric composition. This requires in-depth spectroscopic knowledge of the atmospheres of a large and well-defined planet sample for which precise physical, chemical and dynamical information can be obtained. In order to fulfil this ambitious scientific program, EChO was designed as a dedicated survey mission for transit and eclipse spectroscopy capable of observing a large, diverse and well-defined planet sample within its 4-year mission lifetime. The transit and eclipse spectroscopy method, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allows us to measure atmospheric signals from the planet at levels of at least 10 −4 relative to the star. This can only be achieved in conjunction with a carefully designed stable payload and satellite platform. It is also necessary to provide broad instantaneous wavelength coverage to detect as many molecular species as possible, to probe the thermal structure of the planetary atmospheres and to correct for the contaminating effects of the stellar photosphere. This requires wavelength coverage of at least 0.55 to 11 μm with a goal of covering from 0.4 to 16 μm. Only modest spectral resolving power is needed, with R~300 for wavelengths less than 5 μm and R~30 for wavelengths greater than this. The transit
Bulletin de la Société Française de Physique, 2006
En moyenne, on trouve des planètes autour d'environ 10% des étoiles observées. Cette abondance, o... more En moyenne, on trouve des planètes autour d'environ 10% des étoiles observées. Cette abondance, ou plutôt cette probabilité de détection avec les moyens actuels, varie avec la composition chimique de l'étoile et peut atteindre 25% pour des étoiles de forte métallicité, c'est-à-dire riches en éléments plus lourds que He (figure 1). Environ 1% des étoiles possèdent une planète plus massive que Saturne à moins de 0,1 UA. On appelle ces planètes, qui sont les plus faciles à détecter, des « Jupiters Chauds » ou « Pégasides ». Malgré un biais observationnel contraire, l'abondance des planètes décroît vers les masses élevées, chutant fortement au-dessus de 1-2 M J [masse de Jupiter], et augmente fortement lorsque l'on descend vers les faibles masses, ce qui tend à montrer que les planètes sub-saturniennes sont très abondantes. Les systèmes à plusieurs planètes sont assez communs (18 sont actuellement connus), et les excentricités des orbites au-delà de 0,1 UA sont étonnamment élevées (0,25 en moyenne) par rapport à celles qui sont rencontrées dans le système solaire.
Physical and chemical conditions at the surface of the Earth have changed consid-erably during th... more Physical and chemical conditions at the surface of the Earth have changed consid-erably during the last 3.5Ga.1 Oxygen for instance became a major component of the atmosphere 2.3Ga ago. However, during this whole period, and maybe earlier, the Earth was inhabited and ...
Abstract Because of the paucity of geologic samples dating back to the early Earth, trying to unv... more Abstract Because of the paucity of geologic samples dating back to the early Earth, trying to unveil the nature of the prebiotic terrestrial environ-ment is as frustrating as it is fascinating. An understanding of the characteristics of this period in our planet's history is, however, crucial to studies of ...
In a famous paper, Sagan et al. (Sagan et al.1993) analyzed a spectrum of the Earth taken by the ... more In a famous paper, Sagan et al. (Sagan et al.1993) analyzed a spectrum of the Earth taken by the Galileo probe, searching for signatures of life. They concluded that the large amount of O 2 and the simultaneous presence of CH 4 traces are strongly suggestive of biology. The detection of a widespread red-absorbing pigment with no likely mineral origin supports the hypothesis of biophotosynthesis. The search for signs of life on possibly very different planets implies that we need to gather as much information as possible in order to understand how the observed atmosphere physically and chemically works. The Earth-Sun intensity ratio is about 10 −7 in the thermal infrared (∼ 10 µm), and about 10 −10 in the visible (∼ 0.5 µm). The interferometric systems suggested for Darwin and the Terrestrial Planet Finder Interferometer (TPF-I) mission operates in the mid-IR (5-20 µm), the coronagraph suggested for Terrestrial Planet Finder Coronagraph (TPF-C) in the visible (0.5-1 µm). For the former it is thus the thermal emission emanating from the planet that is detected and analyzed while for the later the reflected stellar flux is measured. The spectrum of the planet can contain signatures of atmospheric species that are important for habitability, like CO 2 and H 2 O, or result from biological activity (O 2 , O 3 , CH 4 , and N 2 O). Both spectral regions contain atmospheric bio-indicators: CO 2 , H 2 O, O 3 , CH 4 , and N 2 O in the thermal infrared, and H 2 O, O 3 , O 2 , CH 4 and CO 2 in the visible to near-infrared. The presence or absence of these spectral features will indicate similarities or differences with the atmospheres of terrestrial planets and are discussed in detail and set into context with the physical characteristics of a planet in this chapter 1 .
The Kepler-186 system consists of five planets orbiting an early M dwarf. The planets have physic... more The Kepler-186 system consists of five planets orbiting an early M dwarf. The planets have physical radii of 1.0-1.50 R ⊕ and orbital periods of 4-130 days. The 1.1R ⊕ Kepler-186f with a period of 130 days is of particular interest. Its insolation of roughly 0.32 S ⊕ places it within the surface liquid water habitable zone (HZ). We present a multifaceted study of the Kepler-186 system, using two sets of parameters which are consistent with the data and also self-consistent. First, we show that the distribution of planet masses can be roughly reproduced if the planets were accreted from a high surface density disk presumably sculpted by an earlier phase of migration. However, our simulations predict the existence of one to two undetected planets between planets e and f. Next, we present a dynamical analysis of the system including the effect of tides. The timescale for tidal evolution is short enough that the four inner planets must have small obliquities and near-synchronous rotation rates. The tidal evolution of Kepler-186f is slow enough that its current spin state depends on a combination of its initial spin state, its dissipation rate, and the stellar age. Finally, we study the habitability of Kepler-186f with a one-dimensional climate model. The planet's surface temperature can be raised above 273 K with 0.5-5 bars of CO 2 , depending on the amount of N 2 present. Kepler-186f represents a case study of an Earth-sized planet in the cooler regions of the HZ of a cool star.
The eccentric orbits of the known extrasolar giant planets provide evidence that most planet-form... more The eccentric orbits of the known extrasolar giant planets provide evidence that most planet-forming environments undergo violent dynamical instabilities. Here, we numerically simulate the impact of giant planet instabilities on planetary systems as a whole. We find that populations of inner rocky and outer icy bodies are both shaped by the giant planet dynamics and are naturally correlated. Strong instabilities-those with very eccentric surviving giant planets-completely clear out their inner and outer regions. In contrast, systems with stable or low-mass giant planets form terrestrial planets in their inner regions and outer icy bodies produce dust that is observable as debris disks at mid-infrared wavelengths. Fifteen to twenty percent of old stars are observed to have bright debris disks (at λ ∼ 70µm) and we predict that these signpost dynamically calm environments that should contain terrestrial planets.
Proceedings of the International Astronomical Union, 2010
During the last few years, observations have yielded an abundant population of short-period plane... more During the last few years, observations have yielded an abundant population of short-period planets under 15 Earth masses. Among those, hot terrestrial exoplanets represent a key population to study the survival of dense atmospheres close to their parent star. Thermal emission from exoplanets orbiting low-mass stars will be observable with the next generation of infrared telescopes, in particular the JWST. In order to constrain planetary and atmospheric properties, we have developed models to simulate the variation of the infrared emission along the path of the orbit (IR phase curve) for both airless planets and planets with dense atmospheres. Here, we focus on airless planets and present preliminary results on the influence of orbital elements, planet rotation, surface properties and observation geometry. Then, using simulated noisy phase curves, we test the retrieval of planets' properties and identify the degeneracies.
Morphological Biosignatures Accretion, Trapping and Binding of Sediment in Archean Stromatolites-... more Morphological Biosignatures Accretion, Trapping and Binding of Sediment in Archean Stromatolites-Morphological Expression of the Antiquity of Life W. Altermann 55 Biogenerated Rock Structures W.E. Krumbein 81 Morphological Biosignatures in Early Terrestrial and Extraterrestrial Materials F. Westall 95 Molecular Biosignatures Gene Transfer and the Reconstruction of Life's Early History from Genomic Data
Proceedings of the International Astronomical Union, 2010
The science of extra-solar planets is one of the most rapidly changing areas of astrophysics and ... more The science of extra-solar planets is one of the most rapidly changing areas of astrophysics and since 1995 the number of planets known has increased by almost two orders of magnitude. A combination of ground-based surveys and dedicated space missions has resulted in 560-plus planets being detected, and over 1200 that await confirmation. NASA's Kepler mission has opened up the possibility of discovering Earth-like planets in the habitable zone around some of the 100,000 stars it is surveying during its 3 to 4-year lifetime. The new ESA's Gaia mission is expected to discover thousands of new planets around stars within 200 parsecs of the Sun. The key challenge now is moving on from discovery, important though that remains, to characterisation: what are these planets actually like, and why are they as they are?In the past ten years, we have learned how to obtain the first spectra of exoplanets using transit transmission and emission spectroscopy. With the high stability of Spi...
Detecting terrestrial planets around nearby stars will considerably expand the field of planetary... more Detecting terrestrial planets around nearby stars will considerably expand the field of planetary sciences. More challenging than the direct detection itself, the analysis of planetary spectra will give precious constraints on the planetary formation processes, the origin and evolution of the atmospheres and the habitability of the planets. This scientific input will however depend on the instrument characteristics and the spectral domain observed (reflected light or thermal emission). In this paper, we investigate the ways to characterize terrestrial exoplanets and their atmosphere, focusing on the science at (very) low resolution.
The dissipation of the tidal energy deposited on eccentric planets may induce a heating of the pl... more The dissipation of the tidal energy deposited on eccentric planets may induce a heating of the planet that affects its atmospheric thermal structure. Here we study the influence of tidal heating on the atmospheric composition of the eccentric (e = 0.16) "hot Neptune" GJ 436b, for which inconclusive chemical abundances are retrieved from multiwavelength photometric observations carried out during primary transit and secondary eclipse. We build up a one-dimensional model of GJ 436b's atmosphere in the vertical direction and compute the pressure-temperature and molecular abundances profiles for various plausible internal temperatures of the planet (up to 560 K) and metallicities (from solar to 100 times solar), using a radiative-convective model and a chemical model which includes thermochemical kinetics, vertical mixing, and photochemistry. We find that the CO/CH 4 abundance ratio increases with metallicity and tidal heating, and ranges from 1/20 to 1000 within the ranges of metallicity and internal temperature explored. Water vapor locks most of the oxygen and reaches a very high abundance, whatever the metallicity and internal temperature of the planet. The CO 2 /H 2 O abundance ratio increases dramatically with metallicity, and takes values between 10 −5-10 −4 with solar elemental abundances and ∼0.1 for a metallicity 100 times solar. None of the atmospheric models based on solid physical and chemical grounds provide a fully satisfactory agreement with available observational data, although the comparison of calculated spectra and observations seems to point to models with a high metallicity and efficient tidal heating, in which high CO/CH 4 abundance ratios and warm temperatures in the dayside atmosphere are favored.
Starry Brightness The high photometric precision of NASA's Kepler observatory has enabled the... more Starry Brightness The high photometric precision of NASA's Kepler observatory has enabled the detection of many planets because they cause slight dimming of their host stars as they orbit in front of them. From these data, Quintana et al. (p. 277 ) have spotted a five-planet system around a small star. Here, the outermost planet is only 10% larger than Earth and completes its 130-day orbit entirely within the habitable zone, where liquid water could exist on its surface. Similarly, Kepler can detect faint periodic brightenings, as Kruse and Agol (p. 275 ) have reported for the binary system KOI-3278. In this system, a white dwarf acts as a gravitational microlens when it passes in front of its Sun-like G-star companion every 88 days. The lensing effect allows the mass of the white dwarf to be estimated, which helps us to understand how similar binary systems may have evolved.
We review recent theoretical progress aimed at understanding the formation and the early stages o... more We review recent theoretical progress aimed at understanding the formation and the early stages of evolution of giant planets, low-mass stars and brown dwarfs. Calculations coupling giant planet formation, within a modern version of the core accretion model, and subsequent evolution yield consistent determinations of the planet structure and evolution. Because of the uncertainties in the initial conditions, however, it is not possible to say whether young planets are faint or bright compared with low-mass young brown dwarfs. We review the effects of irradiation and evaporation on the evolution of short period planets and argue that substantial mass loss may have occurred for these objects. Concerning star formation, geometrical effects in protostar core collapse are examined by comparing 1D and 3D calculations. Spherical collapse is shown to overestimate the core inner density and temperature and thus to yield incorrect initial conditions for PMS or young brown dwarf evolution. Accr...
Planets less massive than about 10 MEarth are expected to have no massive H-He atmosphere and a c... more Planets less massive than about 10 MEarth are expected to have no massive H-He atmosphere and a cometary composition (50% rocks, 50% water, by mass) provided they formed beyond the snowline of protoplanetary disks. Due to inward migration, such planets could be found at any distance between their formation site and the star. If migration stops within the habitable zone, this will produce a new kind of planets, called Ocean-Planets. Ocean-planets typically consist in a silicate core, surrounded by a thick ice mantle, itself covered by a 100 km deep ocean. The existence of ocean-planets raises important astrobiological questions: Can life originate on such body, in the absence of continent and ocean-silicate interfaces? What would be the nature of the atmosphere and the geochemical cycles ? In this work, we address the fate of Hot Ocean-Planets produced when migration ends at a closer distance. In this case the liquid/gas interface can disappear, and the hot H2O envelope is made of a ...
One aim of modern astronomy is to detect temperate, Earth-like exoplanets that are well suited fo... more One aim of modern astronomy is to detect temperate, Earth-like exoplanets that are well suited for atmospheric characterization. Recently, three Earth-sized planets were detected that transit (that is, pass in front of) a star with a mass just eight per cent that of the Sun, located 12 parsecs away. The transiting configuration of these planets, combined with the Jupiter-like size of their host star-named TRAPPIST-1-makes possible in-depth studies of their atmospheric properties with present-day and future astronomical facilities. Here we report the results of a photometric monitoring campaign of that star from the ground and space. Our observations reveal that at least seven planets with sizes and masses similar to those of Earth revolve around TRAPPIST-1. The six inner planets form a near-resonant chain, such that their orbital periods (1.51, 2.42, 4.04, 6.06, 9.1 and 12.35 days) are near-ratios of small integers. This architecture suggests that the planets formed farther from the...
The discovery of almost two thousand exoplanets has revealed an unexpectedly diverse planet popul... more The discovery of almost two thousand exoplanets has revealed an unexpectedly diverse planet population. We see gas giants in few-day orbits, whole multi-planet systems within the orbit of Mercury, and new populations of planets with masses between that of the Earth and Neptune-all unknown in the Solar System. Observations to date have shown that our Solar System is certainly not representative of the general population of planets in our Milky Way. The key science questions that urgently need addressing are therefore: What are exoplanets made of? Why are planets as they are? How do planetary systems work and what causes the exceptional diversity observed as compared to the Solar System? The EChO (Exoplanet Characterisation Observatory) space mission was conceived to take up the challenge to explain this diversity in terms of formation, evolution, internal structure and planet and atmospheric composition. This requires in-depth spectroscopic knowledge of the atmospheres of a large and well-defined planet sample for which precise physical, chemical and dynamical information can be obtained. In order to fulfil this ambitious scientific program, EChO was designed as a dedicated survey mission for transit and eclipse spectroscopy capable of observing a large, diverse and well-defined planet sample within its 4-year mission lifetime. The transit and eclipse spectroscopy method, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allows us to measure atmospheric signals from the planet at levels of at least 10 −4 relative to the star. This can only be achieved in conjunction with a carefully designed stable payload and satellite platform. It is also necessary to provide broad instantaneous wavelength coverage to detect as many molecular species as possible, to probe the thermal structure of the planetary atmospheres and to correct for the contaminating effects of the stellar photosphere. This requires wavelength coverage of at least 0.55 to 11 μm with a goal of covering from 0.4 to 16 μm. Only modest spectral resolving power is needed, with R~300 for wavelengths less than 5 μm and R~30 for wavelengths greater than this. The transit
Bulletin de la Société Française de Physique, 2006
En moyenne, on trouve des planètes autour d'environ 10% des étoiles observées. Cette abondance, o... more En moyenne, on trouve des planètes autour d'environ 10% des étoiles observées. Cette abondance, ou plutôt cette probabilité de détection avec les moyens actuels, varie avec la composition chimique de l'étoile et peut atteindre 25% pour des étoiles de forte métallicité, c'est-à-dire riches en éléments plus lourds que He (figure 1). Environ 1% des étoiles possèdent une planète plus massive que Saturne à moins de 0,1 UA. On appelle ces planètes, qui sont les plus faciles à détecter, des « Jupiters Chauds » ou « Pégasides ». Malgré un biais observationnel contraire, l'abondance des planètes décroît vers les masses élevées, chutant fortement au-dessus de 1-2 M J [masse de Jupiter], et augmente fortement lorsque l'on descend vers les faibles masses, ce qui tend à montrer que les planètes sub-saturniennes sont très abondantes. Les systèmes à plusieurs planètes sont assez communs (18 sont actuellement connus), et les excentricités des orbites au-delà de 0,1 UA sont étonnamment élevées (0,25 en moyenne) par rapport à celles qui sont rencontrées dans le système solaire.
Physical and chemical conditions at the surface of the Earth have changed consid-erably during th... more Physical and chemical conditions at the surface of the Earth have changed consid-erably during the last 3.5Ga.1 Oxygen for instance became a major component of the atmosphere 2.3Ga ago. However, during this whole period, and maybe earlier, the Earth was inhabited and ...
Abstract Because of the paucity of geologic samples dating back to the early Earth, trying to unv... more Abstract Because of the paucity of geologic samples dating back to the early Earth, trying to unveil the nature of the prebiotic terrestrial environ-ment is as frustrating as it is fascinating. An understanding of the characteristics of this period in our planet's history is, however, crucial to studies of ...
In a famous paper, Sagan et al. (Sagan et al.1993) analyzed a spectrum of the Earth taken by the ... more In a famous paper, Sagan et al. (Sagan et al.1993) analyzed a spectrum of the Earth taken by the Galileo probe, searching for signatures of life. They concluded that the large amount of O 2 and the simultaneous presence of CH 4 traces are strongly suggestive of biology. The detection of a widespread red-absorbing pigment with no likely mineral origin supports the hypothesis of biophotosynthesis. The search for signs of life on possibly very different planets implies that we need to gather as much information as possible in order to understand how the observed atmosphere physically and chemically works. The Earth-Sun intensity ratio is about 10 −7 in the thermal infrared (∼ 10 µm), and about 10 −10 in the visible (∼ 0.5 µm). The interferometric systems suggested for Darwin and the Terrestrial Planet Finder Interferometer (TPF-I) mission operates in the mid-IR (5-20 µm), the coronagraph suggested for Terrestrial Planet Finder Coronagraph (TPF-C) in the visible (0.5-1 µm). For the former it is thus the thermal emission emanating from the planet that is detected and analyzed while for the later the reflected stellar flux is measured. The spectrum of the planet can contain signatures of atmospheric species that are important for habitability, like CO 2 and H 2 O, or result from biological activity (O 2 , O 3 , CH 4 , and N 2 O). Both spectral regions contain atmospheric bio-indicators: CO 2 , H 2 O, O 3 , CH 4 , and N 2 O in the thermal infrared, and H 2 O, O 3 , O 2 , CH 4 and CO 2 in the visible to near-infrared. The presence or absence of these spectral features will indicate similarities or differences with the atmospheres of terrestrial planets and are discussed in detail and set into context with the physical characteristics of a planet in this chapter 1 .
The Kepler-186 system consists of five planets orbiting an early M dwarf. The planets have physic... more The Kepler-186 system consists of five planets orbiting an early M dwarf. The planets have physical radii of 1.0-1.50 R ⊕ and orbital periods of 4-130 days. The 1.1R ⊕ Kepler-186f with a period of 130 days is of particular interest. Its insolation of roughly 0.32 S ⊕ places it within the surface liquid water habitable zone (HZ). We present a multifaceted study of the Kepler-186 system, using two sets of parameters which are consistent with the data and also self-consistent. First, we show that the distribution of planet masses can be roughly reproduced if the planets were accreted from a high surface density disk presumably sculpted by an earlier phase of migration. However, our simulations predict the existence of one to two undetected planets between planets e and f. Next, we present a dynamical analysis of the system including the effect of tides. The timescale for tidal evolution is short enough that the four inner planets must have small obliquities and near-synchronous rotation rates. The tidal evolution of Kepler-186f is slow enough that its current spin state depends on a combination of its initial spin state, its dissipation rate, and the stellar age. Finally, we study the habitability of Kepler-186f with a one-dimensional climate model. The planet's surface temperature can be raised above 273 K with 0.5-5 bars of CO 2 , depending on the amount of N 2 present. Kepler-186f represents a case study of an Earth-sized planet in the cooler regions of the HZ of a cool star.
The eccentric orbits of the known extrasolar giant planets provide evidence that most planet-form... more The eccentric orbits of the known extrasolar giant planets provide evidence that most planet-forming environments undergo violent dynamical instabilities. Here, we numerically simulate the impact of giant planet instabilities on planetary systems as a whole. We find that populations of inner rocky and outer icy bodies are both shaped by the giant planet dynamics and are naturally correlated. Strong instabilities-those with very eccentric surviving giant planets-completely clear out their inner and outer regions. In contrast, systems with stable or low-mass giant planets form terrestrial planets in their inner regions and outer icy bodies produce dust that is observable as debris disks at mid-infrared wavelengths. Fifteen to twenty percent of old stars are observed to have bright debris disks (at λ ∼ 70µm) and we predict that these signpost dynamically calm environments that should contain terrestrial planets.
Proceedings of the International Astronomical Union, 2010
During the last few years, observations have yielded an abundant population of short-period plane... more During the last few years, observations have yielded an abundant population of short-period planets under 15 Earth masses. Among those, hot terrestrial exoplanets represent a key population to study the survival of dense atmospheres close to their parent star. Thermal emission from exoplanets orbiting low-mass stars will be observable with the next generation of infrared telescopes, in particular the JWST. In order to constrain planetary and atmospheric properties, we have developed models to simulate the variation of the infrared emission along the path of the orbit (IR phase curve) for both airless planets and planets with dense atmospheres. Here, we focus on airless planets and present preliminary results on the influence of orbital elements, planet rotation, surface properties and observation geometry. Then, using simulated noisy phase curves, we test the retrieval of planets' properties and identify the degeneracies.
Morphological Biosignatures Accretion, Trapping and Binding of Sediment in Archean Stromatolites-... more Morphological Biosignatures Accretion, Trapping and Binding of Sediment in Archean Stromatolites-Morphological Expression of the Antiquity of Life W. Altermann 55 Biogenerated Rock Structures W.E. Krumbein 81 Morphological Biosignatures in Early Terrestrial and Extraterrestrial Materials F. Westall 95 Molecular Biosignatures Gene Transfer and the Reconstruction of Life's Early History from Genomic Data
Proceedings of the International Astronomical Union, 2010
The science of extra-solar planets is one of the most rapidly changing areas of astrophysics and ... more The science of extra-solar planets is one of the most rapidly changing areas of astrophysics and since 1995 the number of planets known has increased by almost two orders of magnitude. A combination of ground-based surveys and dedicated space missions has resulted in 560-plus planets being detected, and over 1200 that await confirmation. NASA's Kepler mission has opened up the possibility of discovering Earth-like planets in the habitable zone around some of the 100,000 stars it is surveying during its 3 to 4-year lifetime. The new ESA's Gaia mission is expected to discover thousands of new planets around stars within 200 parsecs of the Sun. The key challenge now is moving on from discovery, important though that remains, to characterisation: what are these planets actually like, and why are they as they are?In the past ten years, we have learned how to obtain the first spectra of exoplanets using transit transmission and emission spectroscopy. With the high stability of Spi...
Detecting terrestrial planets around nearby stars will considerably expand the field of planetary... more Detecting terrestrial planets around nearby stars will considerably expand the field of planetary sciences. More challenging than the direct detection itself, the analysis of planetary spectra will give precious constraints on the planetary formation processes, the origin and evolution of the atmospheres and the habitability of the planets. This scientific input will however depend on the instrument characteristics and the spectral domain observed (reflected light or thermal emission). In this paper, we investigate the ways to characterize terrestrial exoplanets and their atmosphere, focusing on the science at (very) low resolution.
The dissipation of the tidal energy deposited on eccentric planets may induce a heating of the pl... more The dissipation of the tidal energy deposited on eccentric planets may induce a heating of the planet that affects its atmospheric thermal structure. Here we study the influence of tidal heating on the atmospheric composition of the eccentric (e = 0.16) "hot Neptune" GJ 436b, for which inconclusive chemical abundances are retrieved from multiwavelength photometric observations carried out during primary transit and secondary eclipse. We build up a one-dimensional model of GJ 436b's atmosphere in the vertical direction and compute the pressure-temperature and molecular abundances profiles for various plausible internal temperatures of the planet (up to 560 K) and metallicities (from solar to 100 times solar), using a radiative-convective model and a chemical model which includes thermochemical kinetics, vertical mixing, and photochemistry. We find that the CO/CH 4 abundance ratio increases with metallicity and tidal heating, and ranges from 1/20 to 1000 within the ranges of metallicity and internal temperature explored. Water vapor locks most of the oxygen and reaches a very high abundance, whatever the metallicity and internal temperature of the planet. The CO 2 /H 2 O abundance ratio increases dramatically with metallicity, and takes values between 10 −5-10 −4 with solar elemental abundances and ∼0.1 for a metallicity 100 times solar. None of the atmospheric models based on solid physical and chemical grounds provide a fully satisfactory agreement with available observational data, although the comparison of calculated spectra and observations seems to point to models with a high metallicity and efficient tidal heating, in which high CO/CH 4 abundance ratios and warm temperatures in the dayside atmosphere are favored.
Starry Brightness The high photometric precision of NASA's Kepler observatory has enabled the... more Starry Brightness The high photometric precision of NASA's Kepler observatory has enabled the detection of many planets because they cause slight dimming of their host stars as they orbit in front of them. From these data, Quintana et al. (p. 277 ) have spotted a five-planet system around a small star. Here, the outermost planet is only 10% larger than Earth and completes its 130-day orbit entirely within the habitable zone, where liquid water could exist on its surface. Similarly, Kepler can detect faint periodic brightenings, as Kruse and Agol (p. 275 ) have reported for the binary system KOI-3278. In this system, a white dwarf acts as a gravitational microlens when it passes in front of its Sun-like G-star companion every 88 days. The lensing effect allows the mass of the white dwarf to be estimated, which helps us to understand how similar binary systems may have evolved.
We review recent theoretical progress aimed at understanding the formation and the early stages o... more We review recent theoretical progress aimed at understanding the formation and the early stages of evolution of giant planets, low-mass stars and brown dwarfs. Calculations coupling giant planet formation, within a modern version of the core accretion model, and subsequent evolution yield consistent determinations of the planet structure and evolution. Because of the uncertainties in the initial conditions, however, it is not possible to say whether young planets are faint or bright compared with low-mass young brown dwarfs. We review the effects of irradiation and evaporation on the evolution of short period planets and argue that substantial mass loss may have occurred for these objects. Concerning star formation, geometrical effects in protostar core collapse are examined by comparing 1D and 3D calculations. Spherical collapse is shown to overestimate the core inner density and temperature and thus to yield incorrect initial conditions for PMS or young brown dwarf evolution. Accr...
Uploads
Papers by Franck Selsis