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Advancements in our understanding of exoplanetary atmospheres, from massive gas giants down to rocky worlds, depend on the constructive challenges between observations and models. We are now on a clear trajectory for improvements in…
Liquid water is a critical component of habitability. However, the production and stability of surficial liquid water can be challenging on planets outside the Habitable Zone and devoid of adequate greenhouse warming. On such cold, icy…
Exoplanet habitability is traditionally assessed by comparing a planet's semi-major axis to the location of its host star's "habitable zone," the shell around a star for which Earth-like planets can possess liquid surface water. The Kepler…
The circumstellar habitable zone and its various refinements serves as a useful entry point for discussing the potential for a planet to generate and sustain life. But little attention is paid to the quality of available energy in the form…
Future telescopes will characterize rocky exoplanets in reflected light, revealing their albedo, which depends on surface, cloud, and atmospheric properties. Identifying these features is crucial for assessing habitability. We present…
Traditionally, the search for life on exoplanets has been predominantly focused on rocky exoplanets. Hycean worlds are a class of habitable sub-Neptunes with planet-wide oceans and H2-rich atmospheres. Their broad range of possible sizes…
[Abridged] To simulate the kinds of observations that will eventually be obtained for exoplanets, the Deep Impact spacecraft obtained light curves of Earth at seven wavebands spanning 300-1000 nm as part of the EPOXI mission of opportunity.…
Planetary obliquity (axial tilt) plays an important role in regulating the climate evolution and habitability of water-covered planets. Despite the suspicion of large obliquities in several exoplanetary systems, this phenomenon remains hard…
Recent observations of the Earth's exosphere revealed the presence of an extended hydrogenic component that could reach distances beyond 40 planetary radii. Detection of similar extended exospheres around Earth-like exoplanets could reveal…
Large terrestrial planets are expected to have muted topography and deep oceans, implying that most super-Earths should be entirely covered in water, so-called waterworlds. This is important because waterworlds lack a silicate weathering…
As the characterization of exoplanet atmospheres proceeds, providing insights into atmospheric chemistry and composition, a key question is how much deeper into the planet we might be able to see from its atmospheric properties alone. For…
In support of the Astrobiology Science Strategy, this whitepaper outlines some key technology challenges pertaining to the remote search for life in exoplanetary systems. Finding evidence for life on rocky planets outside of our solar…
The search for habitable exoplanets and life beyond the Solar System is one of the most compelling scientific opportunities of our time. Nevertheless, the high cost of building facilities that can address this topic and the keen public…
In the last few years astronomical surveys have expanded the reach of planetary science into the realm of small and dense extrasolar worlds. These share a number of characteristics with the terrestrial and icy planetary objects of the Solar…
It remains to be ascertained whether sub-Neptune exoplanets primarily possess hydrogen-rich atmospheres or whether a population of H$_2$O-rich "water worlds" lurks in their midst. Addressing this question requires improved modeling of…
The availability of bioessential elements for "life as we know it", such as phosphorus (P) or possibly molybdenum (Mo), is expected to restrict the biological productivity of extraterrestrial biospheres. Here, we consider worlds with…
Tidal interactions between short-period exoplanets and their host stars drive orbital decay and have likely led to engulfment of planets by their stars. Precise transit timing surveys, with baselines now spanning decades for some planets,…
All life on Earth needs water. NASA's quest to follow the water links water to the search for life in the cosmos. Telescopes like JWST and mission concepts like HabEx, LUVOIR and Origins are designed to characterise rocky exoplanets…
In recent years, numerical models that were developed for Earth have been adapted to study exoplanetary climates to understand how the broad range of possible exoplanetary properties affects their climate state. The recent discovery and…
Exoplanetary science continues to excite and surprise with its rich diversity. We discuss here some key aspects potentially influencing the range of exoplanetary terrestrial-type atmospheres which could exist in nature. We are motivated by…