The habitable zone is the main tool that mission architectures utilize to select potentially habitable planets for follow up spectroscopic observation. Given its importance, the precise size and location of the habitable zone remains a hot topic, as many studies, using a hierarchy of models, have assessed various factors including: atmospheric composition, time, and planetary mass. However, little work has assessed how the habitable zone changes with variations in background nitrogen pressure, which is directly connected to the habitability and life bearing potential of planets. Here, I use an advanced energy balance model with clouds to show that our solar system habitable zone is about 0.9 to 1.7 AU, assuming a 5 bar nitrogen background pressure and a maximum 100 percent cloud cover at the inner edge. This width is about 20 percent wider than the conservative habitable zone estimate. Similar extensions are calculated for A to M stars. I also show that cooling clouds and hazes and high background pressures can decrease the runaway greenhouse threshold temperature to approximately 300 K (or less) for planets orbiting any star type. This is because the associated increase in planetary albedo enables stable climates closer to the star, where rapid destabilization can be triggered from a lower mean surface temperature. Enhanced longwave emission for planets with very high stratospheric temperatures also permits stable climates at smaller orbital distances. The model predicts a runaway greenhouse above approximately 330 K for planets orbiting the Sun, which is consistent with previous work. However, moist greenhouses only occur for planets orbiting A-stars.
We show that collision-induced absorption allows molecular hydrogen to act as an incondensible greenhouse gas, and that bars or tens of bars of primordial H2-He mixtures can maintain surface temperatures above the freezing point of water well beyond the "classical" habitable zone defined for CO2 greenhouse atmospheres. Using a 1-D radiative-convective model we find that 40 bars of pure H2 on a 3 Earth-mass planet can maintain a surface temperature of 280K out to 1.5AU from an early-type M dwarf star and 10 AU from a G-type star. Neglecting the effects of clouds and of gaseous absorbers besides…
Ongoing and future space missions aim to identify potentially habitable planets in our Solar System and beyond. Planetary habitability is determined not only by a planet's current stellar insolation and atmospheric properties, but also by the evolutionary history of its climate. It has been suggested that icy planets and moons become habitable after their initial ice shield melts as their host stars brighten. Here we show from global climate model simulations that a habitable state is not achieved in the climatic evolution of those icy planets and moons that possess an inactive carbonate-silic…
Planets similar to Earth - but slightly more irradiated - are expected to enter into a runaway greenhouse state, where all surface water rapidly evaporates, forming an optically thick H2O-dominated atmosphere. For Earth, this extreme climate transition is thought to occur for a ~6% increase only of the solar luminosity, though the exact limit at which the transition would occur is still a highly debated topic. In general, the runaway greenhouse is believed to be a fundamental process in the evolution of Earth-size, temperate planets. Using 1-D radiative-convective climate calculations accounti…
The habitable zone (HZ) is the circumstellar region where standing bodies of liquid water could exist on the surface of a rocky planet. Conventional definitions assume that CO2 and H2O are the only greenhouse gases. The outer edge of this classical N2-CO2-H2O HZ extends out to nearly 1.7 AU in our solar system, beyond which condensation and scattering by CO2 outstrip its greenhouse capacity. We use a single column radiative-convective climate model to assess the greenhouse effect of CH4 (10 to about 100,000 ppm) on the classical habitable zone (N2-CO2-H2O) for main-sequence stars with stellar …
Young terrestrial planets can capture or outgas hydrogen-rich atmospheres with tens to hundreds of bars of H2, which persist for 100 Myrs or longer. Although the earliest habitable conditions on Earth and terrestrial exoplanets could thus arise while the atmosphere is still dominated by H2, the climatic effects of H2 remain poorly understood. Previous work showed that H2 induces strong greenhouse warming at the outer edge of the habitable zone. Here we use a 1D radiative-convective model to show that H2 also leads to strong warming near the inner edge of the habitable zone. Unlike H2's greenho…
The low temperatures and high ultraviolet (UV) radiation levels at the surface of Mars today currently preclude the survival of life anywhere except perhaps in limited subsurface niches. Several ideas for making the martian surface more habitable have been put forward previously, but they all involve massive environmental modification that will be well beyond human capability for the foreseeable future. Here we present a new approach to this problem. We show that widespread regions of the surface of Mars could be made habitable to photosynthetic life in the future via a solid-state analogue to…
Liquid water is one of the most important materials affecting the climate and habitability of a terrestrial planet. Liquid water vaporizes entirely when planets receive insolation above a certain value, which is called the runaway greenhouse threshold. This threshold forms the inner most limit of the habitable zone. Here, we investigate the effect of the distribution of surface water on the runaway greenhouse threshold for Earth-sized planets using a three-dimensional dynamic atmosphere model. We considered a 1-bar atmosphere whose composition is similar to the current Earth's atmosphere with …
We investigate the habitability of hypothethical moons orbiting known exoplanets. This study focuses on big, rocky exomoons that are capable of maintaining a significant atmosphere. To determine their habitability, we calculate the incident stellar radiation and the tidal heating flux arising in the moons as the two main contributors to the energy budget. We use the runaway greenhouse and the maximum greenhouse flux limits as a definition of habitability. For each exoplanet we run our calculations for plausible ranges of physical and orbital parameters for the moons and the planet using a Mont…
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…
The habitable zone (HZ) around a star is typically defined as the region where a rocky planet can maintain liquid water on its surface. That definition is appropriate, because this allows for the possibility that carbon-based, photosynthetic life exists on the planet in sufficient abundance to modify the planet's atmosphere in a way that might be remotely detected. Exactly what conditions are needed, however, to maintain liquid water remains a topic for debate. Historically, modelers have restricted themselves to water-rich planets with CO2 and H2O as the only important greenhouse gases. More …
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…
A key item of interest for planetary scientists and astronomers is the habitable zone, or the distance from a host star where a terrestrial planet can maintain necessary temperatures in order to retain liquid water on its surface. However, when observing a system's habitable zone, it is possible that one may instead observe a Venus-like planet. We define "Venus-like" as greenhouse-gas-dominated atmosphere occurring when incoming solar radiation exceeds infrared radiation emitted from the planet at the top of the atmosphere, resulting in a runaway greenhouse. Our definition of Venus-like includ…
The ongoing discoveries of extrasolar planets are unveiling a wide range of terrestrial mass (size) planets around their host stars. In this letter, we present estimates of habitable zones (HZs) around stars with stellar effective temperatures in the range 2600 K - 7200 K, for planetary masses between 0.1 ME and 5 ME. Assuming H2O (inner HZ) and CO2 (outer HZ) dominated atmospheres, and scaling the background N2 atmospheric pressure with the radius of the planet, our results indicate that larger planets have wider HZs than do smaller ones. Specifically, with the assumption that smaller planets…
A large number of studies have responded to the growing body of confirmed terrestrial habitable zone exoplanets by presenting models of various possible climates. However, the impact of the partial pressure of background gases such as N$_2$ has not yet been well-explored, despite the abundance of N$_2$ in Earth's atmosphere and the lack of constraints on its typical abundance in terrestrial planet atmospheres. We use PlaSim, a fast 3D climate model, to simulate many hundreds of climates around Sun-like stars with varying N$_2$ partial pressures, instellations, and surface characteristics to id…
White and brown dwarfs are astrophysical objects that are bright enough to support an insolation habitable zone (IHZ). Unlike hydrogen-burning stars, they cool and become less luminous with time, and hence their IHZ moves in with time. The inner edge of the IHZ is defined as the orbital radius at which a planet may enter a moist or runaway greenhouse, phenomena that can remove a planet's surface water forever. Thus, as the IHZ moves in, planets that enter it may no longer have any water, and are still uninhabitable. Additionally, the close proximity of the IHZ to the primary leads to concern t…
Terrestrial planets in the habitable zones (HZs) of low-mass stars and cool dwarfs have received significant scrutiny recently because their shorter orbital periods increase their chances of detection and characterization compared to planets around G-dwarfs. As these planets are likely tidal-locked, improved 3D numerical simulations of such planetary atmospheres are needed to guide target selection. Here we use a 3-D climate system model, updated with new water-vapor absorption coefficients derived from the HITRAN 2012 database, to study ocean covered planets at the inner edge of the HZ around…
We explore the minimum distance from a host star where an exoplanet could potentially be habitable in order not to discard close-in rocky exoplanets for follow-up observations. We find that the inner edge of the Habitable Zone for hot desert worlds can be as close as 0.38 AU around a solar-like star, if the greenhouse effect is reduced ($\sim$ 1% relative humidity) and the surface albedo is increased. We consider a wide range of atmospheric and planetary parameters such as the mixing ratios of greenhouse gases (water vapor and CO$_2$), surface albedo, pressure and gravity. Intermediate surface…
Planets residing in circumstellar habitable zones (CHZs) offer our best opportunities to test hypotheses of life's potential pervasiveness and complexity. Constraining the precise boundaries of habitability and its observational discriminants is critical to maximizing our chances at remote life detection with future instruments. Conventionally, calculations of the inner edge of the habitable zone (IHZ) have been performed using both 1D radiative-convective and 3D general circulation models. However, these models lack interactive three-dimensional chemistry and do not resolve the mesosphere and…
We examine the effect of varying background N2 surface pressure (labelled as pN2) on the inner edge of the habitable zone for 1:1 tidally locked planets around M dwarfs, using the three-dimensional (3D) atmospheric general circulation model (AGCM) ExoCAM. In our experiments, the rotation period is fixed when varying the stellar flux, in order to more clearly isolate the role of pN2. We find that the stellar flux threshold for the runaway greenhouse is a non-monotonous function of pN2. This is due to the competing effects of five processes: pressure broadening, heat capacity, lapse rate, relati…
We report on the discovery and validation of Kepler-452b, a transiting planet identified by a search through the 4 years of data collected by NASA's Kepler Mission. This possibly rocky 1.63$^{+0.23}_{-0.20}$ R$_\oplus$ planet orbits its G2 host star every 384.843$^{+0.007}_{0.012}$ days, the longest orbital period for a small (R$_p$ < 2 R$_\oplus$) transiting exoplanet to date. The likelihood that this planet has a rocky composition lies between 49% and 62%. The star has an effective temperature of 5757$\pm$85 K and a log g of 4.32$\pm$0.09. At a mean orbital separation of 1.046$^{+0.019}_{-0.…
A radiative-convective climate model is used to calculate stratospheric temperatures and water vapor concentrations for ozone-free atmospheres warmer than that of modern Earth. Cold, dry stratospheres are predicted at low surface temperatures, in agreement with recent 3-D calculations. However, at surface temperatures above 350 K, the stratosphere warms and water vapor becomes a major upper atmospheric constituent, allowing water to be lost by photodissociation and hydrogen escape. Hence, a 'moist greenhouse' explanation for loss of water from Venus, or some exoplanet receiving a comparable am…
The Kepler space telescope has detected transits of objects as small as the Earth's Moon, and moons as small as 0.2 Earth masses can be detected in the Kepler data by transit timing and transit duration variations of their host planets. Such massive moons around giant planets in the stellar habitable zone (HZ) could serve as habitats for extraterrestrial life. We here assess the danger of exomoons to be in a runaway greenhouse (RG) state due to extensive heating from the planet. We apply pre-computed evolution tracks for giant planets to calculate the incident planetary radiation on the moon a…
There are four different stable climate states for pure water atmospheres, as might exist on so-called "waterworlds". I map these as a function of solar constant for planets ranging in size from Mars size to 10 Earth-mass. The states are: globally ice covered (Ts< 245K), cold and damp (270 < Ts< 290K), hot and moist (350< Ts< 550K) and very hot and dry (Ts< 900K). No stable climate exists for 290< Ts < 350K or 550 < Ts < 900K. The union of hot moist and cold damp climates describe the liquid water habitable zone, the width and location of which depends on planet mass. At each solar constant, t…
A terrestrial planet in an orbit far outside of the standard habitable zone could maintain surface liquid water as a result of H2-H2 collision-induced absorption by a thick H2 atmosphere. Without a stabilizing climate feedback, however, habitability would be accidental and likely brief. In this letter I propose stabilizing climate feedbacks for such a planet that require only that biological functions have an optimal temperature and operate less efficiently at other temperatures. For example, on a planet with a net source of H2 from its interior, H2-consuming life (such as methanogens) could e…
Conventional definitions of habitability require abundant liquid surface water to exist continuously over geologic timescales. Water in each of its thermodynamic phases interacts with solar and thermal radiation and is the cause for strong climatic feedbacks. Thus, assessments of the habitable zone require models to include a complete treatment of the hydrological cycle over geologic time. Here, we use the Community Atmosphere Model from the National Center for Atmospheric Research to study the evolution of climate for an Earth-like planet at constant CO2, under a wide range of stellar fluxes …
We show that terrestrial planets in the habitable zones of M dwarfs older than $\sim$ 1 Gyr could have been in runaway greenhouses for several hundred Myr following their formation due to the star's extended pre-main sequence phase, provided they form with abundant surface water. Such prolonged runaway greenhouses can lead to planetary evolution divergent from that of Earth. During this early runaway phase, photolysis of water vapor and hydrogen/oxygen escape to space can lead to the loss of several Earth oceans of water from planets throughout the habitable zone, regardless of whether the esc…
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 …
Identifying terrestrial planets in the habitable zones (HZs) of other stars is one of the primary goals of ongoing radial velocity and transit exoplanet surveys and proposed future space missions. Most current estimates of the boundaries of the HZ are based on 1-D, cloud-free, climate model calculations by Kasting et al.(1993). The inner edge of the HZ in Kasting et al.(1993) model was determined by loss of water, and the outer edge was determined by the maximum greenhouse provided by a CO2 atmosphere. A conservative estimate for the width of the HZ from this model in our Solar system is 0.95-…
The potential habitability of known exoplanets is often categorized by a nominal equilibrium temperature assuming a Bond albedo of either 0.3, similar to Earth, or 0. As an indicator of habitability, this leaves much to be desired, because albedo on other planets can be very different, and because surface temperature exceeds equilibrium temperature due to the atmospheric greenhouse effect. We use an ensemble of 3-dimensional general circulation model simulations to show that for a range of habitable planets, much of the variability of Bond albedo, equilibrium temperature, and even surface temp…
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 …
Carbon dioxide is one of the major contributors to the radiative forcing, increasing both the temperature and the humidity of Earth's atmosphere. If the stellar irradiance increases and water becomes abundant in the stratosphere of an Earth-like planet, it will be dissociated and the resultant hydrogen will escape from the atmosphere. This state is called the moist greenhouse threshold (MGT). Using a global climate model (GCM) of intermediate complexity, we explore how to identify this state for different CO2 concentrations and including the radiative effect of atmospheric ozone for the first …
Traditionally stellar radiation has been the only heat source considered capable of determining global climate on long timescales. Here we show that terrestrial exoplanets orbiting low-mass stars may be tidally heated at high enough levels to induce a runaway greenhouse for a long enough duration for all the hydrogen to escape. Without hydrogen, the planet no longer has water and cannot support life. We call these planets "Tidal Venuses," and the phenomenon a "tidal greenhouse." Tidal effects also circularize the orbit, which decreases tidal heating. Hence, some planets may form with large ecc…
The habitable zone (HZ) is the circular region around a star(s) where standing bodies of water could exist on the surface of a rocky planet. Space missions employ the HZ to select promising targets for follow-up habitability assessment. The classical HZ definition assumes that the most important greenhouse gases for habitable planets orbiting main-sequence stars are CO2 and H2O. Although the classical HZ is an effective navigational tool, recent HZ formulations demonstrate that it cannot thoroughly capture the diversity of habitable exoplanets. Here, I review the planetary and stellar processe…
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…
The habitable zone for exomoons with Earth-like properties is a non-trivial manifold, compared to that of Earth-like exoplanets. The presence of tidal heating, eclipses and planetary illumination in the exomoon energy budget combine to produce both circumstellar and circumplanetary habitable regions. Analytical calculations suggest that the circumplanetary habitable region is defined only by an inner edge (with its outer limits determined by orbital stability). Subsequent calculations using 1D latitudinal climate models indicated that the combined effect of eclipses and ice-albedo feedback can…
A rigorous definition of the habitable zone and its dependence on planetary properties is part of the search for habitable exoplanets. In this work, we use the general circulation model ExoCAM to determine how the inner edge of the habitable zone of tidally locked planets orbiting M dwarf stars depends on planetary radius, surface gravity, and surface pressure. We find that the inner edge of the habitable zone for more massive planets occurs at higher stellar irradiation, as found in previous one-dimensional simulations. We also determine the relative effects of varying planetary radius and su…
It is likely that unambiguous habitable zone terrestrial planets of unknown water content will soon be discovered. Water content helps determine surface land fraction, which influences planetary weathering behavior. This is important because the silicate weathering feedback determines the width of the habitable zone in space and time. Here a low-order model of weathering and climate, useful for gaining qualitative understanding, is developed to examine climate evolution for planets of various land-ocean fractions. It is pointed out that, if seafloor weathering does not depend directly on surfa…
Understanding when global glaciations occur on Earth-like planets is a major challenge in climate evolution research. Most models of how greenhouse gases like CO2 evolve with time on terrestrial planets are deterministic, but the complex, nonlinear nature of Earth's climate history motivates study of non-deterministic climate models. Here a maximally simple stochastic model of CO2 evolution and climate on an Earth-like planet with an imperfect CO2 thermostat is investigated. It is shown that as stellar luminosity is increased in this model, the decrease in the average atmospheric CO concentrat…
The classical habitable zone is the circular region around a star in which liquid water could exist on the surface of a rocky planet. The outer edge of the traditional N2-CO2-H2O habitable zone (HZ) extends out to nearly 1.7 AU in our Solar System, beyond which condensation and scattering by CO2 outstrips its greenhouse capacity. Here, we show that volcanic outgassing of atmospheric H2 on a planet near the outer edge can extend the habitable zone out to ~2.4 AU in our solar system. This wider volcanic hydrogen habitable zone (N2-CO2-H2O-H2) can be sustained as long as volcanic H2 output offset…
With most planets and planetary candidates detected in the stellar habitable zone (HZ) being super-Earths and gas giants, rather than Earth-like planets, we naturally wonder if their moons could be habitable. The first detection of such an exomoon has now become feasible, and due to observational biases it will be at least twice as massive as Mars. But formation models predict moons can hardly be as massive as Earth. Hence, a giant planet's magnetosphere could be the only possibility for such a moon to be shielded from cosmic and stellar high-energy radiation. Yet, the planetary radiation belt…
We calculate the pre-main-sequence HZ for stars of spectral classes F to M. The spatial distribution of liquid water and its change during the pre-main-sequence phase of protoplanetary systems is important in understanding how planets become habitable. Such worlds are interesting targets for future missions because the coolest stars could provide habitable conditions for up to 2.5 billion years post-accretion. Moreover, for a given star type, planetary systems are more easily resolved because of higher pre-main-sequence stellar luminosities, resulting in larger planet to star separation for co…
In order to recognize a habitable exoplanet from future observed spectra, we present new model reflected spectra and geometric albedo for modern and prebiotic (3.9 Ga) Earth-like exoplanets orbiting within the habitable zone of stars of spectral types F, G, K and M. We compute this for various atmospheric and surface compositions of the planets. Molecules that are potential biosignatures and act as greenhouse agents are incorporated in our model atmosphere. Various combinations of solid and liquid materials such as ocean, coast, land consisting of trees, grass, sand or rocks determine the surf…
The habitable zone (HZ) is the region around a star(s) where standing bodies of water could exist on the surface of a rocky planet. The classical HZ definition makes a number of assumptions common to the Earth, including assuming that the most important greenhouse gases for habitable planets are CO2 and H2O, habitable planets orbit main-sequence stars, and that the carbonate-silicate cycle is a universal process on potentially habitable planets. Here, we discuss these and other predictions for the habitable zone and the observations that are needed to test them. We also, for the first time, ar…
We report the detection of GJ 832c, a super-Earth orbiting near the inner edge of the habitable zone of GJ 832, an M dwarf previously known to host a Jupiter analog in a nearly-circular 9.4-year orbit. The combination of precise radial-velocity measurements from three telescopes reveals the presence of a planet with a period of 35.68+/-0.03 days and minimum mass (m sin i) of 5.4+/-1.0 Earth masses. GJ 832c moves on a low-eccentricity orbit (e=0.18+/-0.13) towards the inner edge of the habitable zone. However, given the large mass of the planet, it seems likely that it would possess a massive a…
In Paper I and II, a comprehensive approach was utilized for the calculation of S-type and P-type habitable regions in stellar binary systems for both circular and elliptical orbits of the binary components. It considered a joint constraint including orbital stability and a habitable region for a possible system planet through the stellar radiative energy fluxes ("radiative habitable zone"; RHZ). Specifically, the stellar S-type and P-type RHZs are calculated based on the solution of a fourth order polynomial. However, in concurrent developments, mostly during 2013 and 2014, important improvem…
Here, we evaluate our nearest planetary neighbor, Venus, as an exemplar of the runaway greenhouse state that bounds the inner edge of the habitable zone. Despite its current hellish surface environment, Venus may once have been habitable with oceans of surface liquid water. Over time, it lost its potentially clement environment as the sun brightened. Today, it represents the end-state of habitable planet evolution, and it therefore provides valuable lessons on habitability as a planetary process. Beyond the solar system, exo-Venus analogs are likely common types of planets, and we likely have …
TRAPPIST-1 is an ultra-cool dwarf hosting a system consisting of seven planets. While orbital properties, radii and masses of the planets are nowadays well constrained, one of the open fascinating issues is the possibility that an environment hospitable to life could develop on some of these planets. Here we use a simple formulation of an energy balance model that includes the vegetation coverage to investigate the possibility of life affecting the climate of the planets in the TRAPPIST-1 system. Results confirm that planet T-e has the best chance for a habitable world and indicate that vegeta…
Planetary rotation rate is a key parameter in determining atmospheric circulation and hence the spatial pattern of clouds. Since clouds can exert a dominant control on planetary radiation balance, rotation rate could be critical for determining mean planetary climate. Here we investigate this idea using a three-dimensional general circulation model with a sophisticated cloud scheme. We find that slowly rotating planets (like Venus) can maintain an Earth-like climate at nearly twice the stellar flux as rapidly rotating planets (like Earth). This suggests that many exoplanets previously believed…
This paper outlines a simple approach to evaluate habitability of terrestrial planets by assuming different types of planetary atmospheres and using corresponding model calculations. Our approach can be applied for current and future candidates provided by the Kepler mission and other searches. The resulting uncertainties and changes in the number of planetary candidates in the HZ for the Kepler February 2011 data release are discussed. To first order the HZ depends on the effective stellar flux distribution in wavelength and time, the planet albedo, and greenhouse gas effects. We provide a si…
We present an improved estimate of the occurrence rate of small planets orbiting small stars by searching the full four-year Kepler data set for transiting planets using our own planet detection pipeline and conducting transit injection and recovery simulations to empirically measure the search completeness of our pipeline. We identified 156 planet candidates, including one object that was not previously identified as a Kepler Object of Interest. We inspected all publicly available follow-up images, observing notes, and centroid analyses, and corrected for the likelihood of false positives. We…
A planet's climate can be strongly affected by its orbital eccentricity and obliquity. Here we use a 1-dimensional energy balance model modified to include a simple runaway greenhouse (RGH) parameterization to explore the effects of these two parameters on the climate of Earth-like aqua planets - completely ocean-covered planets - orbiting F-, G-, K-, and M-dwarf stars. We find that the range of instellations for which planets exhibit habitable surface conditions throughout an orbit decreases with increasing eccentricity. However, the appearance of temporarily habitable conditions during an or…
