We show that condensation is an efficient particle growth mechanism, leading to growth beyond decimeter-sized pebbles close to an ice line in protoplanetary discs. As coagulation of dust particles is frustrated by bouncing and fragmentation, condensation could be a complementary, or even dominant, growth mode in the early stages of planet formation. Ice particles diffuse across the ice line and sublimate, and vapour diffusing back across the ice line recondenses onto already existing particles, causing them to grow. We develop a numerical model of the dynamical behaviour of ice particles close to the water ice line, approximately 3 AU from the host star. Particles move with the turbulent gas, modelled as a random walk. They also sediment towards the midplane and drift radially towards the central star. Condensation and sublimation are calculated using a Monte Carlo approach. Our results indicate that, with a turbulent alpha-value of 0.01, growth from millimeter to at least decimeter-sized pebbles is possible on a time scale of 1000 years. We find that particle growth is dominated by ice and vapour transport across the radial ice line, with growth due to transport across the atmospheric ice line being negligible. Ice particles mix outwards by turbulent diffusion, leading to net growth across the entire cold region. The resulting particles are large enough to be sensitive to concentration by streaming instabilities, and in pressure bumps and vortices, which can cause further growth into planetesimals. In our model, particles are considered to be homogeneous ice particles. Taking into account the more realistic composition of ice condensed onto rocky ice nuclei might affect the growth time scales, by release of refractory ice nuclei after sublimation. We also ignore sticking and fragmentation in particle collisions. These effects will be the subject of future investigations.
Many extrasolar (bound) terrestrial planets and free-floating (unbound) planets have been discovered. The existence of bound and unbound terrestrial planets with liquid water is an important question, and of particular importance is the question of their habitability. Even for a globally ice-covered planet, geothermal heat from the planetary interior may melt the interior ice, creating an internal ocean covered by an ice shell. In this paper, we discuss the conditions that terrestrial planets must satisfy for such an internal ocean to exist on the timescale of planetary evolution. The question…
The photometric and spectroscopic signatures of habitable planets orbiting FGK stars may be modulated by surface ice coverage. To estimate its frequency and locations, we simulated the climates of hypothetical planets with a 1D energy balance model and assumed that the planets possess properties similar to modern Earth (mass, geography, atmosphere). We first simulated planets with fixed rotational axes and circular orbits, finding that the vast majority (>90%) of planets with habitable surfaces are free of ice. For planets with partial ice coverage, the parameter space for ice caps (interannua…
The present infrared brightness of a planet originates partly from the accretion energy that the planet gained during its formation and hence provides important constraints to the planet formation process. A planet cools down from a hot initial state to the present state by losing energy through radiative emission from its atmosphere. Thus, the atmospheric properties affect the planetary cooling rate. Previous theories of giant planet cooling assume that the atmospheric composition is unchanged throughout evolution. Planet formation theories, however, suggest that the atmospheres especially of…
We model the early stages of planet formation in the Solar System, including continual planetesimal formation, and planetesimal and pebble accretion onto planetary embryos in an evolving disk driven by a disk wind. The aim is to constrain aspects of planet formation that have large uncertainties by matching key characteristics of the Solar System. The model produces a good fit to these characteristics for a narrow range of parameter space. Planetary growth beyond the ice line is dominated by pebble accretion. Planetesimal accretion is more important inside the ice line. Pebble accretion inside…
Previous studies have shown that sea-ice drift effectively promote the onset of a globally ice-covered snowball climate for paleo Earth and for tidally locked planets around low-mass stars. Here, we investigate whether sea-ice drift can influence the stellar flux threshold for a snowball climate onset on rapidly rotating aqua-planets around a Sun-like star. Using a fully coupled atmosphere--land--ocean--sea-ice model with turning on or off sea-ice drift, a circular orbit with no eccentricity (e=0) and an eccentric orbit (e=0.2) are examined. When sea-ice drift is turned off, the stellar flux t…
Recent observations have found a valley in the size distribution of close-in super-Earths that is interpreted as a signpost that close-in super-Earths are mostly rocky in composition. However, new models predict that planetesimals should first form at the water ice line such that close-in planets are expected to have a significant water ice component. Here we investigate the water contents of super-Earths by studying the interplay between pebble accretion, planet migration and disc evolution. Planets' compositions are determined by their position relative to different condensation fronts (ice …
Global climate evolution models for habitable earthlike planets do not consider the effect of ocean salinity on land ice formation through the hydrological cycle. We consider two categories of such planets: planets with deep oceans, but intrinsically high salinities due to the weaker salt removal process by hydrothermal vents; and planets with shallow oceans, where the increase in salt content and decrease in ocean area during the onset of glaciation cause a negative feedback, helping delay the spread of land ice. We developed a toy climate model of a habitable planet on the verge of an ice ag…
Terrestrial planets covered globally with thick oceans (termed ocean planets) in the habitable zone were previously inferred to have extremely hot climates in most cases. This is because ${\rm H_2O}$ high-pressure (HP) ice on the seafloor prevents chemical weathering and, thus, removal of atmospheric CO$_2$. Previous studies, however, ignored melting of the HP ice and horizontal variation in heat flux from oceanic crusts. Here we examine whether high heat fluxes near the mid-ocean ridge melts the HP ice and thereby removes atmospheric ${\rm CO_2}$. We develop integrated climate models of an Ea…
The ice-albedo feedback is a potentially important de-stabilizing effect for the climate of terrestrial planets. It is based on the positive feedback between decreasing surface temperatures, an increase of snow and ice cover and an associated increase in planetary albedo, which then further decreases surface temperature. A recent study shows that for M stars, the strength of the ice-albedo feedback is reduced This study investigates the influence of the atmosphere (in terms of surface pressure and atmospheric composition) for this feedback. A plane-parallel radiative transfer model is used for…
Planetary climate can be affected by the interaction of the host star spectral energy distribution with the wavelength-dependent reflectivity of ice and snow. Here we explore this effect using a one dimensional (1-D), line-by-line, radiative-transfer model to calculate broadband planetary albedos as input to a seasonally varying, 1-D energy-balance climate model. A three-dimensional general circulation model is also used to explore the atmosphere's response to changes in incoming stellar radiation, or instellation, and surface albedo. Using this hierarchy of models we simulate planets covered …
Conventionally, a habitable planet is one that can support liquid water on its surface. Habitability depends on temperature, which is set by insolation and the greenhouse effect, due mainly to CO2 and water vapor. The CO2 level is increased by volcanic outgassing, and decreased by continental and seafloor weathering. Here, I examine the climate evolution of Earth-like planets using a globally averaged climate model that includes both weathering types. Climate is sensitive to the relative contributions of continental and seafloor weathering, even when the total weathering rate is fixed. Climate…
Distant planets in globally ice-covered, "snowball", states may depend on increases in their host stars' luminosity to become hospitable for surface life. Using a General Circulation Model (GCM), we simulated the equilibrium climate response of a planet to a range of instellations from an F-, G-, or M- dwarf star. The range of instellation that permits both complete ice cover and at least partially ice-free climate states is a measure of the climate hysteresis that a planet can exhibit. An ice-covered planet with high climate hysteresis would show a higher resistance to the initial loss of sur…
We consider planets composed of water ice and rock, located far from a central star. In an earlier study, computing the growth of planets by continuous accretion, we found that a large fraction of the ice evaporates upon accretion, creating a water vapor atmosphere. Here we consider accretion as a discrete series of planetesimal impacts (of order $10^8$), at the same time-dependent accretion rate, and investigate the fate of the vapor, as a result of its interaction with the accreting planetesimals. We find that a large fraction of the vapor escapes. The remaining fraction may form an outer la…
Recently Saito & Sirono (2011) proposed that large ice aggregates which drift in- wards in protoplanetary disks break up during sublimation, ejecting embedded silicate particles. This would lead to a concentration of small solid particles close to the snow- line. In view of this model we carried out laboratory experiments where we observed freely levitating ice aggregates sublimating. We find that frequent break up is indeed very common. Scaled to a 10 cm aggregate about 2x10^4 small silicate aggregates might result. This supports the idea that sublimation of drifting ice aggregates might loca…
In protoplanetary disks, CO$_2$ is solid ice beyond its snow line at $\sim 10 \rm AU$. Due to its high abundance, it contributes heavily to the collisional evolution in this region of the disk. For the first time, we carried out laboratory collision experiments with CO$_2$ ice particles and a CO$_2$-covered wall at a temperature of 80 K. Collision velocities varied between 0 - 2.5 m/s. Particle sizes were on the order of $\sim$ 100 $μ$m. We find a threshold velocity between the sticking and the bouncing regime at 0.04 m/s. Particles with greater velocities but below 1 m/s bounce off the wall. …
Ices, including water ice, prefer to recondense onto pre-existing nuclei rather than spontaneously forming grains from a cloud of vapor. Interestingly, different potential recondensation nuclei have very different propensities to actually nucleate water ice at the temperatures associated with freeze-out in protoplanetary discs. Therefore, if a region in a disc is warmed and then recooled, water vapor should not be expected to refreeze evenly onto all available grains. Instead it will preferentially recondense onto the most favorable grains. When the recooling is slow enough, only the most favo…
Ice-rich planets are formed exterior to the water ice-line and thus are expected to contain a substantial amount of ices. The high ice content leads to unique conditions in the interior, under which the structure of a planet is affected by ice interaction with other metals. We apply experimental data of ice-rock interaction at high pressure, and calculate detailed thermal evolution for possible interior configurations of ice-rich planets, in the mass range of super-Earth to Neptunes (5-15 Earth masses). We model the effect of migration inward on the ice-rich interior by including the influence…
In the Solar System giant planets come in two flavours: 'gas giants' (Jupiter and Saturn) with massive gas envelopes and 'ice giants' (Uranus and Neptune) with much thinner envelopes around their cores. It is poorly understood how these two classes of planets formed. High solid accretion rates, necessary to form the cores of giant planets within the life-time of protoplanetary discs, heat the envelope and prevent rapid gas contraction onto the core, unless accretion is halted. We find that, in fact, accretion of pebbles (~ cm-sized particles) is self-limiting: when a core becomes massive enoug…
We explore planet formation in the HL Tau disk and possible origins of the prominent gaps and rings observed by ALMA. We investigate whether dust gaps are caused by dynamically trapped planetary embryos at the ice lines of abundant volatiles. The global properties of the HL Tau disk (total mass, size) at its current age are used to constrain an evolving analytic disk model describing its temperature and density profiles. By performing a detailed analysis of the planet-disk interaction for a planet near the water ice line including a rigorous treatment of the dust opacity, we confirm that water…
The climates of terrestrial planets with a small amount of water on their surface, called land planets, are significantly different from the climates of planets having a large amount of surface water. Land planets have a higher runaway greenhouse threshold than aqua planets, which extends the inner edge of the habitable zone inward. Land planets also have the advantage of avoiding global freezing due to drier tropics, leading to a lower planetary albedo. In this study, we systematically investigate the complete freezing limit for various surface water distribution using a three-dimensional dyn…
The Martian climate is governed by an annual cycle, that results in the condensation of CO$_{2}$ ice during winter, up to a meter thick at the pole and thousands of kilometers in extension. Water and dust may be trapped during the condensation and freed during the sublimation. In addition, ice may be translucent or granular depending on the deposition process (snow vs direct condensation), annealing efficiency, and dust sinking process. The determination of ice translucency is of particular interest to confirm or reject the cold jet model (also known as Kieffer model). This work is focused on …
Exomoon detections might be feasible with NASA's Kepler or ESA's upcoming PLATO mission or the ground-based E-ELT. To use observational resources most efficiently we need to know where the largest, most easily detected moons can form. We explore the possibility of large exomoons by following the movement of water (H2O) ice lines in the accretion disks around young super-Jovian planets. We want to know how different heating sources in those disks affect the H2O ice lines. We simulate 2D rotationally symmetric accretion disks in hydrostatic equilibrium around super-Jovian exoplanets. The energy …
The habitable zone is the region around a star where standing bodies of liquid water can be stable on a planetary surface. Its width is often assumed to be dictated by the efficiency of the carbonate-silicate cycle, which has maintained habitable surface conditions on our planet for billions of years. This cycle may be inhibited by surface condensation of significant amounts of $CO_{\mathrm{2}}$ ice, which is likely to occur on distant planets containing high enough levels of atmospheric $CO_{\mathrm{2}}$. Such a process could permanently trap $CO_{\mathrm{2}}$ ice within the planet, threateni…
It is widely believed that the carbonate-silicate cycle is the main agent to trigger deglaciations by CO$_2$ greenhouse warming on Earth and on Earth-like planets when they get in frozen state. Here we use a 3D Global Climate Model to simulate the ability of frozen planets to escape from glaciation by accumulating enough gaseous CO$_2$. We find that Earth-like planets orbiting a Sun-like star may never be able to escape from glaciation if their orbital distance is greater than $\sim$ 1.27 AU (Flux $<$ 847 W m$^{-2}$ or 62$\%$ of the Solar constant), because CO$_2$ would condense at the poles f…
Models of planet formation have shown that giant planets have a large impact on the number, masses and orbits of terrestrial planets that form. In addition, they play an important role in delivering volatiles from material that formed exterior to the snow-line (the region in the disk beyond which water ice can condense) to the inner region of the disk where terrestrial planets can maintain liquid water on their surfaces. We present simulations of the late stages of terrestrial planet formation from a disk of protoplanets around a solar-type star, and we include a massive planet (from 1 Earth m…
Using an energy balance model with ice sheets, we examine the climate response of an Earth-like planet orbiting a G dwarf star and experiencing large orbital and obliquity variations. We find that ice caps couple strongly to the orbital forcing, leading to extreme ice ages. In contrast with previous studies, we find that such exo-Milankovitch cycles tend to impair habitability by inducing snowball states within the habitable zone. The large amplitude changes in obliquity and eccentricity cause the ice edge, the lowest latitude extent of the ice caps, to become unstable and grow to the equator.…
Owing to their wavelengths dependent absorption and scattering properties, clouds have a strong impact on the climate of planetary atmospheres. Especially, the potential greenhouse effect of CO2 ice clouds in the atmospheres of terrestrial extrasolar planets is of particular interest because it might influence the position and thus the extension of the outer boundary of the classic habitable zone around main sequence stars. We study the radiative effects of CO2 ice particles obtained by different numerical treatments to solve the radiative transfer equation. The comparison between the results …
The thermodynamic structure of protoplanetary discs is determined by dust opacities, which depend on the size of the dust grains and their chemical composition. In the inner regions, the grain sizes are regulated by the level of turbulence (e.g. $α$ viscosity) and by the dust fragmentation velocity that represents the maximal velocity that grains can have at a collision before they fragment. Here, we perform self-consistently calculated 2D hydrodynamical simulations that consider a full grain size distribution of dust grains with a transition in the dust fragmentation velocity at the water-ice…
We present collision experiments of centimetre projectiles on to decimetre targets, both made up of solid ice, at velocities of $15\,\mathrm{m\,s^{-1}}$ to $45\,\mathrm{m\,s^{-1}}$ at an average temperature of $\mathrm{T_{avg}}=255.8\pm0.7\,\mathrm{K}$. In these collisions the centimetre body gets disrupted and part of it sticks to the target. This behaviour can be observed up to an upper threshold, that depends on the projectile size, beyond which there is no mass transfer. In collisions of small particles, as produced by the disruption of the centimetre projectiles, we also find mass transfe…
The gas giant planets in the Solar System have a retinue of icy moons, and we expect giant exoplanets to have similar satellite systems. If a Jupiter-like planet were to migrate toward its parent star the icy moons orbiting it would evaporate, creating atmospheres and possible habitable surface oceans. Here, we examine how long the surface ice and possible oceans would last before being hydrodynamically lost to space. The hydrodynamic loss rate from the moons is determined, in large part, by the stellar flux available for absorption, which increases as the giant planet and icy moons migrate cl…
Surface liquid water is essential for standard planetary habitability. Calculations of atmospheric circulation on tidally locked planets around M stars suggest that this peculiar orbital configuration lends itself to the trapping of large amounts of water in kilometers-thick ice on the night side, potentially removing all liquid water from the day side where photosynthesis is possible. We study this problem using a global climate model including coupled atmosphere, ocean, land, and sea-ice components as well as a continental ice sheet model driven by the climate model output. For a waterworld …
To reveal the formation of planetesimals it is of great importance to understand the collision behavior of the dusty and icy aggregates they have formed from. We present an experimental setup to investigate the aggregation properties in low-velocity collisions of dust aggregates, solid ices and icy aggregates under microgravity conditions. Results from ESA's 45th Parabolic Flight Campaign show that most collisions in the velocity range 0.1 m/s < v_c < 0.5m/s are dominated by a rebound behavior of the projectile dust aggregates and only ~ 5% of the translational kinetic energy is conserved afte…
The ever-expanding catalog of detected super-Earths calls for theoretical studies of their properties in the case of a substantial water layer. This work considers such water planets with a range of masses and water mass fractions (2 to 5 M_Earth, 0.02% to 50% H2 O). First, we model the thermal and dynamical structure of the near-surface for icy and oceanic surfaces, finding separate regimes where the planet is expected to maintain a subsurface liquid ocean and where it is expected to exhibit ice tectonics. Newly discovered exoplanets may be placed into one of these regimes given estimates of …
Ice giants are the only unexplored class of planet in our Solar System. Much that we currently know about these systems challenges our understanding of how planets, rings, satellites, and magnetospheres form and evolve. We assert that an ice giant Flagship mission with an atmospheric probe should be a priority for the decade 2023-2032.
The terrestrial planets and the asteroids dominant in the inner asteroid belt are water poor. However, in the protoplanetary disk the temperature should have decreased below water condensation level well before the disk was photoevaporated. Thus, the global water depletion of the inner Solar System is puzling. We show that, even if the inner disk becomes cold, there cannot be direct condensation of water. This is because the snowline moves towards the Sun more slowly than the gas itself. The appearance of ice in a range of heliocentric distances swept by the snowline can only be due to the rad…
We used {\sl \textup{ab initio}} molecular dynamics simulations to calculate the high-pressure melting temperatures of the three potential core components. The planetary adiabats were obtained by solving the hydrostatic equations in a three-layer model adjusted to reproduce the measured gravitational moments. Recently developed {\sl \textup{ab initio}} equations of state were used for the envelope and the core. We find that the cores of the giant and ice-giant planets of the solar system differ because the pressure-temperature conditions encountered in each object correspond to different regio…
Coagulation models assume a higher sticking threshold for micrometer-sized ice particles than for micrometer-sized silicate particles. However, in contrast to silicates, laboratory investigations of the collision properties of micrometer-sized ice particles (in particular, of the most abundant water ice) have not been conducted yet. Thus, we used two different experimental methods to produce micrometer-sized water ice particles, i. e. by spraying water droplets into liquid nitrogen and by spraying water droplets into a cold nitrogen atmosphere. The mean particle radii of the ice particles prod…
The formation mechanisms of the ice giants Uranus and Neptune, and the origin of their elemental and isotopic compositions, have long been debated. The density of solids in the outer protosolar nebula is too low to explain their formation, and spectroscopic observations show that both planets are highly enriched in carbon, very poor in nitrogen, and the ices from which they originally formed might had deuterium-to-hydrogen ratios lower than the predicted cometary value, unexplained properties observed in no other planets. Here we show that all these properties can be explained naturally if Ura…
Carbon dioxide ice clouds are thought to play an important role for cold terrestrial planets with thick CO2 dominated atmospheres. Various previous studies showed that a scattering greenhouse effect by carbon dioxide ice clouds could result in a massive warming of the planetary surface. However, all of these studies only employed simplified two-stream radiative transfer schemes to describe the anisotropic scattering. Using accurate radiative transfer models with a general discrete ordinate method, this study revisits this important effect and shows that the positive climatic impact of carbon d…
Clouds have a strong impact on the climate of planetary atmospheres. The potential scattering greenhouse effect of CO2 ice clouds in the atmospheres of terrestrial extrasolar planets is of particular interest because it might influence the position and thus the extension of the outer boundary of the classic habitable zone around main sequence stars. Here, the impact of CO2 ice clouds on the surface temperatures of terrestrial planets with CO2 dominated atmospheres, orbiting different types of stars is studied. Additionally, their corresponding effect on the position of the outer habitable zone…
Context: Understanding the collisional properties of ice is important for understanding both the early stages of planet formation and the evolution of planetary ring systems. Simple chemicals such as methanol and formic acid are known to be present in cold protostellar regions alongside the dominant water ice; they are also likely to be incorporated into planets which form in protoplanetary disks, and planetary ring systems. However, the effect of the chemical composition of the ice on its collisional properties has not yet been studied. Aims: Collisions of 1.5 cm ice spheres composed of pure …
Most of the exoplanets with known masses at Earth-like distances to Sun-like stars are heavier than Jupiter, which raises the question of whether such planets are accompanied by detectable, possibly habitable moons. Here we simulate the accretion disks around super-Jovian planets and find that giant moons with masses similar to Mars can form. Our results suggest that the Galilean moons formed during the final stages of accretion onto Jupiter, when the circumjovian disk was sufficiently cool. But in contrast to other studies, with our assumptions, we show that Jupiter was still feeding from the…
Planets and their atmospheres are built from gas and solid material in protoplanetary disks. Recent results suggest that solid material like pebbles may contribute significantly to building up planetary atmospheres. In order to link observed exoplanet atmospheres and their compositions to their formation histories, it is important to understand how icy pebbles may change their composition when they drift radially inwards in disks. Our goal is to model the compositional evolution of ices on pebbles as they drift in disks, and track how their chemical evolution en-route changes the ice compositi…
Whether volatiles can be entrapped in a background matrix composing planetary envelopes and be dragged via convection to the surface is a key question in understanding atmospheric fluxes, cycles and composition. In this paper we consider super-Earths with an extensive water mantle (i.e. water planets), and the possibility of entrapment of methane in their extensive water ice envelopes. We adopt the theory developed by van der Waals & Platteeuw (1959) for modelling solid solutions, often used for modelling clathrate hydrates, and modify it in order to estimate the thermodynamic stability field …
A consistent finding of high obliquity simulations is that they are warmer than their low obliquity counterparts when the climate is cold. Ice-albedo feedback has been suggested as a possible mechanism. In this study, we find that warmer climate under high obliquity holds with varying insolations, including almost ice-free conditions. We try to understand the mechanisms through a series of feedback suppression experiments. Turning off the ice-albedo feedback, the temperature contrast between high and low obliquity remains significant, but it vanishes when the cloud radiation effects or the sea…
The polarimetry of the light scattered by planetary surfaces is a powerful tool to provide constraints on their microstructure. To improve the interpretation of polarimetric data from icy surfaces, we have developed the POLarimeter for ICE Samples (POLICES) complementing the measurement facilities of the Ice Laboratory at the University of Bern. The new setup uses a high precision Stokes polarimeter to measure the degree of polarization in the visible light scattered by surfaces at moderate phase angles (from 1.5 to 30°). We present the photometric and polarimetric phase curves measured on var…
We discuss the nature of rings that may exist around extrasolar planets. Taking the general properties of rings around the gas giants in the Solar System, we infer the likely properties of rings around exoplanets that reside inside the ice line. Due to their proximity to their host star, rings around such exoplanets must primarily consist of rocky materials. However, we find that despite the higher densities of rock compared to ice, most of the observed extrasolar planets with reliable radii measurements have sufficiently large Roche radii to support rings. For the currently known transiting e…
Water (H$_{2}$O), in all forms, is an important constituent in planetary bodies, controlling habitability and influencing geological activity. Under conditions found in the interior of many planets, as the pressure increases, the H-bonds in water gradually weaken and are replaced by ionic bonds. Recent experimental measurements of the water equation of state (EOS) showed both a new phase of H-bonded water ice, ice-VII$_t$, and a relatively low transition pressure just above 30 GPa to ionic bonded ice-X, which has a bulk modulus 2.5 times larger. The higher bulk modulus of ice-X produces larger…
Models of the dynamical evolution of the early solar system following the dispersal of the gaseous protoplanetary disk have been widely successful in reconstructing the current orbital configuration of the giant planets. Statistically, some of the most successful dynamical evolution simulations have initially included a hypothetical fifth giant planet, of ice giant mass, which gets ejected by a gas giant during the early solar system's proposed instability phase. We investigate the likelihood of an ice giant ejection event by either Jupiter or Saturn through constraints imposed by the current …
We used high-precision radial velocity measurements of FGKM stars to determine the occurrence of giant planets as a function of orbital separation spanning 0.03-30 au. Giant planets are more prevalent at orbital distances of 1-10 au compared to orbits interior or exterior of this range. The increase in planet occurrence at $\sim$1 au by a factor of $\sim$4 is highly statistically significant. A fall-off in giant planet occurrence at larger orbital distances is favored over models with flat or increasing occurrence. We measure $14.1^{+2.0}_{-1.8}$ giant planets per 100 stars with semi-major axe…
M-stars comprise 80% of main-sequence stars, and so their planetary systems provide the best chance for finding habitable planets, i.e.: those with surface liquid water. We have modelled the broadband albedo or reflectivity of water ice and snow for simulated planetary surfaces orbiting two observed red dwarf stars (or M-stars) using spectrally resolved data of the Earth's cryosphere. The gradual reduction of the albedos of snow and ice at wavelengths greater than 1 ?m, combined with M-stars emitting a significant fraction of their radiation at these same longer wavelengths, mean that the albe…
Planet atmosphere and hydrosphere compositions are fundamentally set by accretion of volatiles, and therefore by the division of volatiles between gas and solids in planet-forming disks. For hyper-volatiles such as CO, this division is regulated by a combination of binding energies, and by the ability of other ice components to entrap. Water ice is known for its ability to trap CO and other volatile species. In this study we explore whether another common interstellar and cometary ice component, CO2, is able to trap CO as well. We measure entrapment of CO molecules in CO2 ice through temperatu…
Tidally locked terrestrial planets around low-mass stars are the prime targets for future atmospheric characterizations of potentially habitable systems, especially the three nearby ones--Proxima b, TRAPPIST-1e, and LHS 1140b. Previous studies suggest that if these planets have surface ocean they would be in an eyeball-like climate state: ice-free in the vicinity of the substellar point and ice-covered in the rest regions. However, an important component of the climate system--sea ice dynamics has not been well studied in previous studies. A fundamental question is: would the open ocean be sta…
