Since the launch of Kepler and Hubble more than a decade ago, we have come a long way in the quest to find a potentially habitable exoplanet. To date, we have already discovered more than 4000 exoplanets most of which are not suitable for sustaining life. Of all those that can potentially sustain life, A large number has been found rotating synchronously around their parent star, mostly Red dwarf star. Due to their synchronous rotation, these planets receive very uneven stellar heating. Synchronous rotation of these planets causes one side of the planet to permanently face the parent star while the other side remains dark. This results in an extreme climatic condition that is not feasible for sustaining life. Although these theories about exoplanets are well known, a systemic study of habitability of polar regions within an exoplanet using different climate models has not been done yet. Here I review the current literature on tidal locking and its impact on habitability and introduce the concept of habitability in the poles of these exoplanets. I focus on my understanding of the climatic condition in the polar region of the earth and based on that I present the concept of habitability in the poles of these exoplanets.
Detections of massive extrasolar moons are shown feasible with the Kepler space telescope. Kepler's findings of about 50 exoplanets in the stellar habitable zone naturally make us wonder about the habitability of their hypothetical moons. Illumination from the planet, eclipses, tidal heating, and tidal locking distinguish remote characterization of exomoons from that of exoplanets. We show how evaluation of an exomoon's habitability is possible based on the parameters accessible by current and near-future technology.
The long-term habitability of Earth-like planets requires low orbital eccentricities. A secular perturbation from a distant stellar companion is a very important mechanism in exciting planetary eccentricities, as many of the extrasolar planetary systems are associated with stellar companions. Although the orbital evolution of an Earth-like planet in a stellar binary is well understood, the effect of a binary perturbation to a more realistic system containing additional gas giant planets has been very little studied. Here we provide analytic criteria confirmed by a large ensemble of numerical i…
The stability of Earth's climate on geological timescales is enabled by the carbon-silicate cycle that acts as a negative feedback mechanism stabilizing surface temperatures via the intake and outgas of atmospheric carbon. On Earth, this thermostat is enabled by plate tectonics that sequesters outgassed CO2 back into the mantle via weathering and subduction at convergent margins. Here we propose a separate tectonic mechanism -- vertical recycling -- that can serve as the vehicle for CO2 outgassing and sequestration over long timescales. The mechanism requires continuous tidal heating, which ma…
We investigate modons on tidally synchronised extrasolar planets. Modons are highly dynamic, coherent flow structures composed of a pair of storms with opposite signs of vorticity. They are important because they divert flows on the large-scale; and, powered by the intense irradiation from the host star, they are planetary-scale sized and exhibit quasi-periodic life-cycles -- chaotically moving around the planet, breaking and reforming many times over long durations (e.g. thousands of planet days). Additionally, modons transport and mix planetary-scale patches of hot and cold air around the pl…
Stellar radiation has conservatively been used as the key constraint to planetary habitability. We review here the effects of tides, exerted by the host star on the planet, on the evolution of the planetary spin. Tides initially drive the rotation period and the orientation of the rotation axis into an equilibrium state but do not necessarily lead to synchronous rotation. As tides also circularize the orbit, eventually the rotation period does equal the orbital period and one hemisphere will be permanently irradiated by the star. Furthermore, the rotational axis will become perpendicular to th…
The diversity and quantity of moons in the Solar System suggest a manifold population of natural satellites exist around extrasolar planets. Of peculiar interest from an astrobiological perspective, the number of sizable moons in the stellar habitable zones may outnumber planets in these circumstellar regions. With technological and theoretical methods now allowing for the detection of sub-Earth-sized extrasolar planets, the first detection of an extrasolar moon appears feasible. In this review, we summarize formation channels of massive exomoons that are potentially detectable with current or…
M type stars are good targets in the search for habitable extrasolar planets. Because of their low effective temperatures, the habitable zone of M stars is very close to the star itself. For planets close to their stars, tidal heating plays an important role in thermal and orbital evolutions, especially when the planet orbit has a relatively large eccentricity. Although tidal heating interacts with the thermal state and orbit of the planet, such coupled calculations for extrasolar planets around M star have not been conducted. We perform coupled calculations using simple structural and orbital…
We present the first investigation of Th abundances in Solar twins and analogues to understand the possible range of this radioactive element and its effect on rocky planet interior dynamics and potential habitability. The abundances of the radioactive elements Th and U are key components of a planet's energy budget, making up 30% to 50% of the Earth's (Korenaga 2008; Allègre et al. 2001; Schubert et al. 1980; Lyubetskaya & Korenaga 2007; The KamLAND Collaboration 2011; Huang et al. 2013). Radiogenic heat drives interior mantle convection and surface plate tectonics, which sustains a deep carb…
Assessing the Climate and Habitability of Tidally Locked Rocky Exoplanets
INAF – Osservatorio Astronomico di Trieste（意大利国家天体物理研究所的里雅斯特天文台）；CNR – Istituto di Geoscienze e Georisorse（国家研究委员会地球科学与地质资源研究所）；Institute for Fundamental Physics of the Universe（宇宙基础物理研究所）；Centro di Ricerca Nazionale in High Performance Computing, Big Data e Quantum Computing (ICSC)（高性能计算、大数据和量子计算国家研究中心）；Politecnico di Torino – DIATI（都灵理工大学）；CNR – Istituto di Scienze dell’Atmosfera e del Clima（国家研究委员会大气与气候科学研究所）；CSIC-INTA – Centro de Astrobiología（西班牙国家科学研究委员会-国家航空航天技术研究所天体生物学中心）；Università degli Studi di Roma “Tor Vergata”（罗马第二大学）；Università degli Studi di Padova（帕多瓦大学）
Atmospheric Collapse and Habitability on Tidally-Locked Exoplanets
Earth-Life Science Institute, Institute of Science Tokyo（地球生命研究所，东京科学大学）；Department of Earth and Planetary Sciences, Institute of Science Tokyo（地球行星科学系，东京科学大学）；Laboratoire de Météorologie Dynamique/IPSL, CNRS, Sorbonne Université, Ecole Normale Supérieure, PSL Research University, Ecole Polytechnique（气象动力学实验室/IPSL，法国国家科学研究中心，索邦大学，巴黎高等师范学院，PSL研究大学，巴黎综合理工学院）；Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS（波尔多天体物理实验室，波尔多大学，法国国家科学研究中心）；Univ. Grenoble Alpes, CNRS, IPAG（格勒诺布尔阿尔卑斯大学，法国国家科学研究中心，地球与行星物理学研究所）；Institute of Science Tokyo（东京科学大学）
We investigate the obliquity and spin period of Earth-Moon like systems after 4.5 Gyr of tidal evolution with various satellite masses and initial planetary obliquity and discuss their relations to the habitability of the planet. We find three possible outcomes: either i) the system is still evolving, ii) the system is double synchronous or iii) the satellite has collided with the planet. The transition between case i) and ii) is abrupt and occurs at slightly larger satellite mass ($m_s \sim 0.02m_p$) than the lunar mass. We suggest that cases ii) and iii) are less habitable than case i). Usin…
Aims. On Earth, plate tectonics play an integral role in driving the long-term carbon cycle; however, on tidally locked rocky exoplanets alternative tectonic mechanisms driven by tidal stress and tidal heating could serve in an analogous way. Methods. We calculate tidal stress and tidal heating rates to model the likelihood of tectonic activity maintaining stable climates suitable for surface liquid water on tidally locked rocky exoplanets with radii ${R}_{p}$ $\le$ 1.23R$_\oplus$. Results. Applying the tidal models to our sample of 767 tidally locked rocky exoplanets reveals that $\sim$10% of…
Jupiter's radio emission has been linked to its planetary-scale magnetic field, and spacecraft investigations have revealed that most planets, and some moons, have or had a global magnetic field. Generated by internal dynamos, magnetic fields are one of the few remote sensing means of constraining the properties of planetary interiors. For the Earth, its magnetic field has been speculated to be partially responsible for its habitability, and knowledge of an extrasolar planet's magnetic field may be necessary to assess its habitability. The radio emission from Jupiter and other solar system pla…
Planets in the "Habitable Zones" around M-type stars are important targets for characterization in future observations. Due to tidal-locking in synchronous spin-orbit rotations, the planets tend to have a hot dayside and a cold nightside. On the cold nightside, water vapor transferred from the dayside can be frozen in ("cold trap") or the major atmospheric constituent could also condense ("atmospheric collapse") if the atmosphere is so thin that the heat re-distribution is not efficient, in the case of a single M-type star. Motivated by the abundance of binary star systems, we investigate the …
Habitability of Tidally Heated H$_2$-Dominated Exomoons around Free-Floating Planets
Ludwig-Maximilians-Universität München（慕尼黑大学）；Max-Planck-Institut für extraterrestrische Physik（马克斯·普朗克地外物理研究所）；Exzellenzcluster ‘Origins’（起源卓越集群）；European Space Agency (ESA)（欧洲空间局）；European Space Astronomy Centre (ESAC)（欧洲空间天文中心）；European Southern Observatory（欧洲南方天文台）
While the solar system contains as many as about 20 times more moons than planets, no moon has been definitively detected around any of the thousands of extrasolar planets so far. The question naturally arises why an exomoon detection has not yet been achieved. This cumulative habilitation thesis covers three of the key aspects related to the ongoing search for extrasolar moons: 1. the possible formation scenarios for moons around extrasolar planets; 2. new detection strategies for these moons; and 3. the potential of exomoons as hosts to extrasolar life. This work is structured as follows. Pa…
The proportions of oxygen, carbon and major rock-forming elements (e.g. Mg, Fe, Si) determine a planet's dominant mineralogy. Variation in a planet's mineralogy subsequently affects planetary mantle dynamics as well as any deep water or carbon cycle. Through thermodynamic models and high pressure diamond anvil cell experiments, we demonstrate the oxidation potential of C is above that of Fe at all pressures and temperatures indicative of 0.1 - 2 Earth-mass planets. This means that for a planet with (Mg+2Si+Fe+2C)/O > 1, excess C in the mantle will be in the form of diamond. We model the genera…
Stellar flares present challenges to the potential habitability of terrestrial planets orbiting M dwarf stars through inducing changes in the atmospheric composition and irradiating the planet's surface in large amounts of ultraviolet light. To examine their impact, we have coupled a general circulation model with a photochemical kinetics scheme to examine the response and changes of an Earth-like atmosphere to stellar flares and coronal mass ejections. We find that stellar flares increase the amount of ozone in the atmosphere by a factor of 20 compared to a quiescent star. We find that corona…
The TRAPPIST-1, Proxima Centauri, and LHS 1140 systems are the most exciting prospects for future follow-up observations of potentially inhabited planets. All orbit nearby M-stars and are likely tidally locked in 1:1 spin-orbit states, which motivates the consideration of the effects that tidal locking might have on planetary habitability. On Earth, periods of global glaciation (snowballs) may have been essential for habitability and remote signs of life (biosignatures) because they are correlated with increases in the complexity of life and in the atmospheric oxygen concentration. In this pap…
We present a model of the Galactic Habitable Zone (GHZ), described in terms of the spatial and temporal dimensions of the Galaxy that may favour the development of complex life. The Milky Way galaxy is modelled using a computational approach by populating stars and their planetary systems on an individual basis using Monte-Carlo methods. We begin with well-established properties of the disk of the Milky Way, such as the stellar number density distribution, the initial mass function, the star formation history, and the metallicity gradient as a function of radial position and time. We vary some…
While recently discovered exotic new planet-types have both challenged our imaginations and broadened our knowledge of planetary system workings, perhaps the most compelling objective of exoplanet science is to detect and characterize habitable and possibly inhabited worlds orbiting in other star systems. For the foreseeable future, characterizations of extrasolar planets will be made via remote sensing of planetary spectroscopic and temporal signals, along with careful fitting of this data to advanced models of planets and their atmospheres. Terrestrial planets are small and significantly mor…
We study the habitability of the two 1-2 Earth-mass planets, recently detected by the CARMENES collaboration, around the ultra-cool nearby M dwarf Teegarden's Star. With orbital periods of 4.9 and 11.4 days, both planets are likely to be within the Habitable Zone and tidally locked. They are among the most Earth-like exoplanets yet discovered. Applying an analytical habitability model we find that surface liquid water could be present on both planets for a wide range of atmospheric properties, which makes them attractive targets for bio-signature searches. The prospects of the planets retainin…
A planet's atmospheric constituents (e.g., O$_2$, O$_3$, H$_2$O$_v$, CO$_2$, CH$_4$, N$_2$O) can provide clues to its surface habitability, and may offer biosignature targets for remote life detection efforts. The plethora of rocky exoplanets found by recent transit surveys (e.g., the Kepler mission) indicates that potentially habitable systems orbiting K- and M-dwarf stars may have very different orbital and atmospheric characteristics than Earth. To assess the physical distribution and observational prospects of various biosignatures and habitability indicators, it is important to understand…
Previous studies have demonstrated that continental carbon-silicate weathering is important to the continued habitability of a terrestrial planet. Despite this, few studies have considered the influence of land on the climate of a tidally-locked planet. In this work we use the Met Office Unified Model, coupled to a land surface model, to investigate the climate effects of a continent located at the sub-stellar point. We choose to use the orbital and planetary parameters of Proxima Centauri B as a template, to allow comparison with the work of others. A region of the surface where $T_{\text{s}}…
Tidal heating of exomoons may play a key role in their habitability, since the elevated temperature can melt the ice on the body even without significant solar radiation. The possibility of life is intensely studied on Solar System moons such as Europa or Enceladus, where the surface ice layer covers tidally heated water ocean. Tidal forces may be even stronger in extrasolar systems, depending on the properties of the moon and its orbit. For studying the tidally heated surface temperature of exomoons, we used a viscoelastic model for the first time. This model is more realistic than the widely…
Identification of habitable planets beyond our solar system is a key goal of current and future space missions. Yet habitability depends not only on the stellar irradiance, but equally on constituent parts of the planetary atmosphere. Here we show, for the first time, that radiatively active mineral dust will have a significant impact on the habitability of Earth-like exoplanets. On tidally-locked planets, dust cools the day-side and warms the night-side, significantly widening the habitable zone. Independent of orbital configuration, we suggest that airborne dust can postpone planetary water …
Terrestrial planets orbiting within the habitable zones of M-stars are likely to become tidally locked in a 1:1 spin:orbit configuration and are prime targets for future characterization efforts. An issue of importance for the potential habitability of terrestrial planets is whether they could experience snowball events (periods of global glaciation). Previous work using an intermediate complexity atmospheric Global Climate Model (GCM) with no ocean heat transport suggested that tidally locked planets would smoothly transition to a snowball, in contrast with Earth, which has bifurcations and h…
The habitability of planets is strongly affected by impacts from comets and asteroids. Indications from the ages of Moon rocks suggest that the inner Solar System experienced an increased rate of impacts roughly 3.8 Gya known as the Late Heavy Bombardment (LHB). Here we develop a model of how the Solar System would have appeared to a distant observer during its history based on the Nice model of Gomes et al. (2005). We compare our results with observed debris discs. We show that the Solar System would have been amongst the brightest of these systems before the LHB. Comparison with the statisti…
The magnetospheric emissions from extrasolar planets represent a science frontier for the next decade. All of the solar system giant planets and the Earth produce radio emissions as a result of interactions between their magnetic fields and the solar wind. In the case of the Earth, its magnetic field may contribute to its habitability by protecting its atmosphere from solar wind erosion and by preventing energetic particles from reaching its surface. Indirect evidence for at least some extrasolar giant planets also having magnetic fields includes the modulation of emission lines of their host …
The aim of my dissertation is to investigate habitability in extra-Solar Systems. Most of the time, only planets are considered as possible places where extraterrestrial life can emerge and evolve, however, their moons could be inhabited, too. I present a comprehensive study, which considers habitability not only on planets, but on satellites, as well. My research focuses on three closely related topics. The first one is the circumstellar habitable zone, which is usually used as a first proxy for determining the habitability of a planet around the host star. The word habitability is used in th…
Our knowledge of planets' orbital dynamics, which was based on Solar System studies, has been challenged by the diversity of exoplanetary systems. Around cool and ultra cool dwarfs, the influence of tides on the orbital and spin evolution of planets can strongly affect their climate and their capacity to host surface liquid water. We illustrate the role of tides and dynamics with the extreme case of planets orbiting around brown dwarfs. In multiple planet systems, the eccentricity is excited by planet-planet interactions. Planets are therefore heated up from the inside by the tidally-induced f…
Atmospheric collapse is likely to be of fundamental importance to tidally locked rocky exoplanets but remains understudied. Here, general results on the heat transport and stability of tidally locked terrestrial-type atmospheres are reported. First, the problem is modeled with an idealized 3D general circulation model (GCM) with gray gas radiative transfer. It is shown that over a wide range of parameters the atmospheric boundary layer, rather than the large-scale circulation, is the key to understanding the planetary energy balance. Through a scaling analysis of the interhemispheric energy tr…
We study the effects of gravity waves, or g-modes, on hot extrasolar planets. These planets are expected to possess stably-stratified atmospheres, which support gravity waves. In this paper, we review the derivation of the equation that governs the linear dynamics of gravity waves and describe its application to a hot extrasolar planet, using HD209458 b as a generic example. We find that gravity waves can exhibit a wide range of behaviors, even for a single atmospheric profile. The waves can significantly accelerate or decelerate the background mean flow, depending on the difference between th…
The potential habitability of a terrestrial planet is usually defined by the possible existence of liquid water on its surface. The potential presence of liquid water depends on many factors such as, most importantly, surface temperatures. The properties of the planetary atmosphere and its interaction with the radiative energy provided by the planet's host star are thereby of decisive importance. In this study we investigate the influence of different main-sequence stars upon the climate of Earth-like extrasolar planets and their potential habitability by applying a 3D Earth climate model acco…
The planetary system around the M star Gliese 581 contains at least three close-in potentially low-mass planets, GL 581 c, d, and e. In order to address the question of the habitability of GL 581 d, we performed detailed atmospheric modeling studies for several planetary scenarios. A 1D radiative-convective model was used to calculate temperature and pressure profiles of model atmospheres, assumed to be composed of molecular nitrogen, water, and carbon dioxide. The model allows for changing surface pressures caused by evaporation/condensation of water and carbon dioxide. Furthermore, the treat…
The detection of moons orbiting extrasolar planets ("exomoons") has now become feasible. Once they are discovered in the circumstellar habitable zone, questions about their habitability will emerge. Exomoons are likely to be tidally locked to their planet and hence experience days much shorter than their orbital period around the star and have seasons, all of which works in favor of habitability. These satellites can receive more illumination per area than their host planets, as the planet reflects stellar light and emits thermal photons. On the contrary, eclipses can significantly alter local…
A new Statistical-likelihood Exo-Planetary Habitability Index (SEPHI) is presented. It has been developed to cover the current and future features required for a classification scheme disentangling whether any discovered exoplanet is potentially habitable compared with life on Earth. The SEPHI uses likelihood functions to estimate the habitability potential. It is defined as the geometric mean of four sub-indexes related with four comparison criteria: Is the planet telluric?; Does it have an atmosphere dense enough and a gravity compatible with life?; Does it have liquid water on its surface?;…
Discoveries of extrasolar planets in the habitable zone (HZ) of their parent star lead to questions about the habitability of massive moons orbiting planets in the HZ. Around low-mass stars, the HZ is much closer to the star than for Sun-like stars. For a planet-moon binary in such a HZ, the proximity of the star forces a close orbit for the moon to remain gravitationally bound to the planet. Under these conditions the effects of tidal heating, distortion torques, and stellar perturbations become important considerations for exomoon habitability. Utilizing a model that considers both dynamical…
Understanding the possible climatic conditions on rocky extrasolar planets, and thereby their potential habitability, is one of the major subjects of exoplanet research. Determining how the climate, as well as potential atmospheric biosignatures, change under different conditions is a key aspect when studying Earth-like exoplanets. One important property is the atmospheric mass hence pressure and its influence on the climatic conditions. Therefore, the aim of the present study is to understand the influence of atmospheric mass on climate, hence habitability, and the spectral appearance of plan…
In a multiverse setting, we expect to be situated in a universe that is exceptionally good at producing life. Though the conditions for what life needs to arise and thrive are currently unknown, many will be tested in the coming decades. Here we investigate several different habitability criteria, and their influence on multiverse expectations: Does complex life need photosynthesis? Is there a minimum timescale necessary for development? Can life arise on tidally locked planets? Are convective stars habitable? Variously adopting different stances on each of these criteria can alter whether our…
In this work, we study the presence of hurricanes on exoplanets. Tidally locked terrestrial planets around M dwarfs are the main targets of space missions looking to discover habitable exoplanets. The question of whether hurricanes can form on this kind of planet is important for determining their climate and habitability. Using a high-resolution global atmospheric circulation model, we investigated whether there are hurricanes on tidally locked terrestrial planets under fixed surface temperatures. The relevant effects of the planetary rotation rate, surface temperature, and bulk atmospheric c…
The detection and characterization of Earth-like planet is approaching rapidly thanks to radial velocity surveys (HARPS), transit searches (Corot, Kepler) and space observatories dedicated to their characterization are already in development phase (James Webb Space Telescope), large ground based telescopes (ELT, TNT, GMT), and dedicated space-based missions like Darwin, Terrestrial Planet Finder, New World Observer). In this paper we discuss how we can read a planets spectrum to assess its habitability and search for the signatures of a biosphere. Identifying signs of life implies understandin…
Detecting massive satellites of extrasolar planets has now become feasible, which led naturally to questions about their habitability. In a previous study we presented constraints on the habitability of moons from stellar and planetary illumination as well as from tidal heating. Here I refine our model by including the effect of eclipses on the orbit-averaged illumination. Moons in low-mass stellar systems must orbit their planet very closely to remain bound, which puts them at risk of strong tidal heating. I first describe the effect of eclipses on stellar illumination of satellites. Then I c…
Eccentricity is an important orbital parameter. Understanding its effect on planetary climate and habitability is critical for us to search for a habitable world beyond our solar system. The orbital configurations of M-dwarf planets are always tidally-locked at resonance states, which are quite different from those around Sun-like stars. M-dwarf planets need to be investigated separately. Here we use a comprehensive three-dimensional atmospheric general circulation model to systematically investigate how eccentricity influences climate and habitability of M-dwarf exoplanets. The simulation res…
We investigate a new class of habitable planets composed of water-rich interiors with massive oceans underlying H2-rich atmospheres, referred to here as Hycean worlds. With densities between those of rocky super-Earths and more extended mini-Neptunes, Hycean planets can be optimal candidates in the search for exoplanetary habitability and may be abundant in the exoplanet population. We investigate the bulk properties (masses, radii, and temperatures), potential for habitability, and observable biosignatures of Hycean planets. We show that Hycean planets can be significantly larger compared to …
Hot Jupiters are a class of extrasolar planet that orbit their parent stars at very short distances. Due to their close proximity, they are expected to be tidally locked, which can lead to a large temperature difference between their day and nightsides. Infrared observations of eclipsing systems have yielded dayside temperatures for a number of transiting planets. Furthermore the day-night contrast of the transiting extrasolar planet HD 189733b was mapped using infrared observations. It is expected that the contrast between the dayside and nightside of hot Jupiters is much higher at visual wav…
The TRAPPIST-1 system provides an extraordinary opportunity to study multiple terrestrial extrasolar planets and their atmospheres. Here we use the National Center for Atmospheric Research Community Atmosphere Model version 4 to study the possible climate and habitability of the planets in the TRAPPIST-1 system. We assume ocean-covered worlds, with atmospheres comprised of N2, CO2, and H2O, and with orbital and geophysical properties defined from observation. Model results indicate that the inner three planets (b, c, and d) presently reside interior to the inner edge of the traditional liquid …
In this paper we discuss how we can read a planets spectrum to assess its habitability and search for the signatures of a biosphere. After a decade rich in giant exoplanet detections, observation techniques have now reached the ability to find planets of less than 10 MEarth (so called Super-Earths) that may potentially be habitable. How can we characterize those planets and assess if they are habitable? The new field of extrasolar planet search has shown an extraordinary ability to combine research by astrophysics, chemistry, biology and geophysics into a new and exciting interdisciplinary app…
A survey of currently known planet-hosting stars indicates that approximately 25% of extrasolar planetary systems are within dual-star environments. Several of these systems contain stellar companions on moderately close orbits, implying that studies of the formation and dynamical evolution of giant and terrestrial planets, in and around binary star systems have now found realistic grounds. With the recent launch of the space telescope CoRoT, and the launch of NASA's Kepler satellite in 2009, the number of such dynamically complex systems will soon increase and many more of their diverse and i…
The discovery of planets orbiting stars other than the Sun has accelerated over the past decade, and this trend will continue as new space- and ground-based observatories employ next-generation instrumentation to search the skies for habitable worlds. However, many factors and processes can affect planetary habitability and must be understood to accurately determine a planet's habitability potential. While climate models have long been used to understand and predict climate and weather patterns on the Earth, a growing community of researchers has begun to apply these models to extrasolar plane…
Contrary to Earth, which has a small orbital eccentricity, some exoplanets discovered in the insolation habitable zone (HZ) have high orbital eccentricities (e.g., up to an eccentricity of $\sim0.97$ for HD~20782~b). This raises the question of the capacity of these planets to host surface liquid water. In order to assess the habitability of an eccentric planet, the mean flux approximation is often used. It states that a planet on an eccentric orbit is called habitable if it receives on average a flux compatible with the presence of surface liquid water. However, as the planets do experience i…
Clouds and hazes are commonplace in the atmospheres of solar system planets and are likely ubiquitous in the atmospheres of extrasolar planets as well. Clouds affect every aspect of a planetary atmosphere, from the transport of radiation, to atmospheric chemistry, to dynamics and they influence - if not control - aspects such as surface temperature and habitability. In this review we aim to provide an introduction to the role and properties of clouds in exoplanetary atmospheres. We consider the role clouds play in influencing the spectra of planets as well as their habitability and detectabili…
Synchronously orbiting, tidally-locked exoplanets with a dayside facing their star and a permanently dark nightside orbiting dim stars are prime candidates for habitability. Simulations of these planets often show the potential to maintain an Earth-like climate with a complete hydrological cycle. Here, we examine the sensitivity of the atmospheric water cycle to changes in stellar flux and describe the main underlying mechanisms. In a slowly-rotating, tidally-locked Earth-like atmospheric model, the response to a small (about 10%) increase in stellar irradiance from a habitable-zone control si…
Moons orbiting extrasolar planets are the next class of object to be observed and characterized for possible habitability. Like the host-planets to their host-star, exomoons have a limiting radius at which they may be gravitationally bound, or the Hill radius. In addition, they also have a distance at which they will become tidally locked and therefore in synchronous rotation with the planet. We have examined the flux phase profile of a simulated, hypothetical moon orbiting at a distant radius around the confirmed exoplanets mu Ara b, HD 28185 b, BD +14 4559 b, and HD 73534 b. The irradiated f…
Cloud is critical for planetary climate and habitability, but it is also one of the most challenging parts of studying planets in and beyond the solar system. Here we use a cloud-resolving model (CRM) with high resolution (2 km) in a two-dimensional (2D) configuration to simulate the clouds and circulation on tidally locked aqua-planets. We find that the substellar area is covered by deep convective clouds, the nightside is dominated by low-level clouds, and these two are linked by a global-scale Walker circulation. We further find that a uniform surface warming causes the substellar cloud wid…
