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Small rocky planets, as well as larger planets that suffered extensive volatile loss, tend to be drier and have thinner atmospheres as compared to Earth. Such planets probably outnumber worlds better endowed with volatiles, being the most…
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…
Ocean-atmosphere chemistry on Earth has undergone dramatic evolutionary changes through its long history, with potentially significant ramifications for the emergence and long-term stability of atmospheric biosignatures. Though a great deal…
Earth's water, intrinsic oxidation state, and metal core density are fundamental chemical features of our planet. Studies of exoplanets provide a useful context for elucidating the source of these chemical traits. Planet formation and…
Volcanism is a major and long-term source of volatile elements such as C and H to Earth's atmosphere, likely has been to Venus's atmosphere, and may be for exoplanets. Models simulating volcanic growth of atmospheres often make one of two…
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…
The Habitable Worlds Observatory (HWO) aims to telescopically constrain the frequency and abundance of biospheres in the solar neighborhood. Origin-of-life theories vary in their predictions for the environmental requirements and the…
For more than 3.5 billion years, life experienced dramatic environmental extremes on Earth. These include shifts from oxygen-less to over-oxygenated atmospheres and cycling between hothouse conditions and global glaciations. Meanwhile, an…
We explore the conditions prevailing in primordial planets in the framework of the HGD cosmologies as discussed by Gibson and Schild. The initial stages of condensation of planet-mass H-4He gas clouds in trillion-planet clumps is set at…
Studying exoplanet atmospheres is essential for assessing their potential to host liquid water and their capacity to support life (their habitability). Each atmosphere uniquely influences the likelihood of surface liquid water, defining the…
Exoplanet hunting efforts have revealed the prevalence of exotic worlds with diverse properties, including Earth-sized bodies, which has fueled our endeavor to search for life beyond the Solar System. Accumulating experiences in…
There is growing evidence that brown dwarfs may be comparable to main-sequence stars in terms of their abundance. In this paper, we explore the prospects for the existence of life on Earth-like planets around brown dwarfs. We consider the…
Earth will become uninhabitable within 2-3 Gyr as a result of the moving boundaries of the habitable zone caused by the increasing luminosity of the Sun. Predictions about the future of habitable conditions on Earth include a decline in…
Global temperature is a fundamental climate metric highly correlated with sea level, which implies that keeping shorelines near their present location requires keeping global temperature within or close to its preindustrial Holocene range.…
Cycling of carbon dioxide between the atmosphere and interior of rocky planets can stabilize global climate and enable planetary surface temperatures above freezing over geologic time. However, variations in global carbon budget and…
Life has had a dramatic impact on the composition of Earth's atmosphere over time, which suggests that statistical studies of other inhabited planets' atmospheres could reveal how they co-evolve with life. While many evolutionary pathways…
Thousands of transiting exoplanets have already been detected orbiting a wide range of host stars, including the first planets that could potentially be similar to Earth. The upcoming Extremely Large Telescopes and the James Webb Space…
The habitable fraction of a planet's surface is important for the detectability of surface biosignatures. The extent and distribution of habitable areas is influenced by external parameters that control the planet's climate, atmospheric…
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…
One of the chief paradoxes of molecular oxygen (O$_2$) is that it is an essential requirement for multicellular eukaryotes on Earth while simultaneously posing a threat to their survival via the formation of reactive oxygen species. In this…