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The atmospheric composition of rocky exoplanets offers an important tool for constraining the properties of the interior of this type of planet, beyond what is possible from measurements of their mass and radius alone. However, the interpretation of these observations requires an understanding of the complex interplay of a larger number of coupled planetary and atmospheric processes. This review provides an overview of the current state of knowledge regarding rocky exoplanet atmospheres, beginning with their formation and escape mechanisms. We specifically highlight the importance of long-term interaction between the atmosphere, the surface, and the interior on rocky planets. Furthermore, this review addresses the influence of biological activity and photochemical reactions on the atmospheric compositions. Consequently, establishing how these different processes contribute to shaping the atmospheres of rocky exoplanets during their evolution is fundamental for the characterization of these planets with future space missions and ground-based surveys.

This article reviews the emerging field of exo-geoscience, focusing on the geological and geophysical processes thought to influence the evolution and (eu)habitability of rocky exoplanets. We examine the possible roles of planetary interiors, tectonic regimes, continental coverage, volatile cycling, magnetic fields, and atmospheric composition and evolution in shaping long-term climate stability and biospheric potential. Comparisons with Earth and other planets in the Solar System highlight the diversity of planetary conditions and the rarity of conditions relevant to life. We also discuss contingency and convergence in planetary and biological evolution as they relate to the spread of life in the universe. The observational limits of current and planned missions are assessed, emphasizing the need for models that connect internal dynamics to detectable atmospheric and surface signatures as well as the need for laboratory measurements of planetary properties under a wide range of conditions. The large number of exoplanets promises opportunities for empirical and statistical studies of processes that may have occurred earlier in Earth's history, as well as for the other pathways rocky planets and biospheres may take. Thus, exo-geoscience provides a framework for interpreting exoplanet diversity and refining strategies for detecting life beyond the Solar System.

The emergence of habitable conditions on the early Earth and on rocky exoplanets requires persistent energy sources that can drive both prebiotic chemistry and climate warming under magnetically active young G-M stars. To quantify the contribution of stellar energetic particle (StEP) events associated with superflares to the atmospheric chemistry of young planets with primitive atmospheres, we carried out a suite of laboratory proton-irradiation experiments on mildly reduced gas mixtures. We present first proton irradiation experiments of N2-CO2-rich gas mixtures that yield abundant nitrous oxide (N2O) at mixing ratios up to similar to 103 ppmv, together with amino acid precursors including glycine, corresponding to global production rates of order 2 & times; 1010 kg yr-1 on the early Earth. Our photochemical modeling of StEP-driven proton irradiation reproduces the experimentally inferred N2O production rates and provides self-consistent atmospheric N2O profiles. We then use these profiles of N2O as input to a 3D global climate model to evaluate the radiative-climatic impact of StEP-generated N2O in primitive atmospheres representative of the early Earth and young rocky exoplanets. Our results show that frequent StEP events can help alleviate the faint young Sun paradox on the early Earth and can maintain temperate surface conditions on young rocky exoplanets beyond the outer edges of the habitable zone, while simultaneously enhancing the buildup of prebiotic molecules. Together, these processes may constitute a robust pathway toward early planetary habitability.

Volatile loss from exoplanetary atmospheres and its possible implications for the longevity of habitable surface conditions is a topic of vigorous debate currently. The vast majority of the habitable zone terrestrial-like exoplanets known to date orbit low-mass M- and K-dwarf stars and are subject to the conditions drastically different to those of terrestrial planets in the Solar System. In particular, they orbit far closer to their host stars than similar planets around G-dwarfs similar to the Sun. Therefore they receive higher X-ray and UV fluxes, even though luminosities of M- and K-dwarfs are lower than those of heavier stars. Furthermore, due to their slower evolution, M-dwarfs retain high activity on the gigayear timescales. The combination of these two effects has led to claims that most terrestrial planets orbiting M-dwarfs may have their atmospheres stripped from the higher X-ray and UV fluxes of their host stars. Opposing this are researchers who point out that volatile inventories for terrestrial exoplanets are ill-constrained, and hence, they may be able to "weather the storm" of these higher X-ray and UV fluxes. In this article, we focus on exploring volatile loss in the upper atmospheres of terrestrial planets in our solar system and applications to those in exoplanetary systems around stars of different types.

The number of rocky extrasolar planets being discovered continues to increase, but so too does the apparent diversity of such worlds. As we work to understand the likely bulk properties and thermal, geological, and climatological attributes we might expect of rocky exoplanets, we can look to the Solar System for guidance. Here, we review the interior, surface, and atmospheric characteristics of modern Earth, and discuss how our homeworld has changed through Solar System history. We then visit in turn Venus, Mars, Mercury and Earth's Moon, and Io, noting how these terrestrial planets are alike, how they are different, and how they have evolved through time. Finally, we consider some examples of the types of rocky worlds known or suspected to exist without direct Solar System counterparts-but we argue that even then, for all the variety we might expect, they are still variations on a common theme. Perhaps the most important lesson the Solar System can teach us is that terrestrial bodies change through time, sometimes dramatically, and that rocky worlds of similar size and mass can have vastly different planetary outcomes.

We report the highest resolution altitude profile and isotopic composition for N-2 at Venus, to date. These results were obtained through re-analysis of data acquired by the Pioneer Venus Large Probe Neutral Mass Spectrometer (LNMS). The N-2 is non-uniformly mixed across the clouds and sub-cloud atmosphere (similar to 59-15 km) yet uniformly mixed across the deep lower atmosphere (DLA, <15 km). The volume percent for N-2 decreases by similar to 2.1-fold between the clouds (5.21 +/- 0.18 vol%; similar to 59-51 km) and DLA (2.49 +/- 0.10 vol%; <15 km) with concomitant increases in the atmospheric molecular masses. Using the cloud N-2, we extracted the N-15/N-14 ratio (2.93 x 10(-3) +/- 0.13 x 10(-3)) and a corresponding delta N-15 (-204 +/- 35 parts per thousand). Together, the LNMS results suggest that (a) N-2 is not well-mixed >15 km, (b) the atmosphere is unstable at <15 km, and (c) the cloud delta N-15 falls between the solar wind and Earth's atmosphere. Plain Language Summary We report the highest resolution altitude profile and isotopic composition for molecular nitrogen (N-2) at Venus, to date. These results were obtained through re-analysis of data acquired by the Pioneer Venus Large Probe Neutral Mass Spectrometer. The Venus N-2 is non-uniformly mixed between the clouds and sub-cloud atmosphere (similar to 59-15 km) yet uniformly mixed in the deep lower atmosphere below 15 km. A decrease in N-2 abundances of similar to 2-fold is observed between the clouds (similar to 59-51 km) and deep lower atmosphere (<15 km). From the cloud N-2, we also extracted a constrained N-15/N-14 ratio. Together, these results suggest that (a) N-2 is not well-mixed above 15 km, (b) the atmosphere is unstable below 15 km, and (c) the N-15/N-14 ratio for Venus' clouds falls between the solar wind and Earth's atmosphere.

In this article, we study the conditions required to maintain a stable ocean on Mars 3 Ga using a new suite of simulations. These simulations couple a 3D Global Climate Model with ocean dynamics and ice sheet flow. The model includes the main processes of the atmosphere/hydrosphere/cryosphere to investigate Mars' ancient climate. The results show that the total water content required to maintain an ocean is ∼ 700m, global equivalent layer, half in the ocean, half in the ice sheet. This number seems plausible if a significant amount of water has been absorbed by the ground. This could be in the form of mineral alteration, or in a deep porous reservoir. In addition, the results show that the equilibrium mass flux from the ice sheet adjacent to the northern ocean is ∼ 10¹⁵ kg/y with a very low sliding velocity (1 m/y), except for few warm regions in the lowest altitudes that could reach up to 300 m/y. Finally, the global atmosphere/hydrosphere/cryosphere equilibrium should be reached in a few 100 ky. This indicates that the ocean will have a stabilizing feedback on timescales longer than this. An extensive sensitivity study of the ice sheet was performed. This included the effects of a geothermal heat flux, viscosity and basal drag. Finally, we studied the possible effects of planetary obliquity and a reduced ocean extent.

The climate and habitability of exoplanets are particularly difficult to constrain due to a lack of planetary information (e.g., obliquity and rotation rate) alongside current observational limitations. Surface water content is one of the most highly sought variables given its connections to the origins of life on Earth. Unfortunately, surface water is impossible to constrain due to uncertainties in (i) water content observations and (ii) surface-mantle water differentiation. Global ocean scenarios are prevalent in the literature, but it is vital to investigate the alternative arid scenarios with varied continental orientations and surface water abundances. Here, we use an ensemble of ROCKE-3D global climate model simulations to investigate the potential habitability of single-continent, land-dominated planets. This ensemble simulates climate over a range of water surface areas (WSAs; global ocean coverage) and continental orientations (pole- and equator-centered continents). We find that pole-centered orientations are 2 degrees C-5 degrees C warmer than equator-centered orientations across most WSAs due to the lack of highlands in the northern pole preventing snow and ice accumulation. These differences between continental orientations are completely diminished under the most arid scenarios. This is due to water limitation that results in a breakdown of the ice-albedo feedback, causing warming. Our results show that both WSA and continental orientation play roles in the global mean surface temperature of exoplanets. Future direct imaging missions, such as the Habitable Worlds Observatory, will play a crucial role in constraining the climate of exoplanets due to their ability to assess surface water and land dichotomies.

As the discovery of exoplanets progresses at a rapid pace, the large number of known planets provides a pathway to assess the stellar and planetary properties that govern the climate evolution of terrestrial planets. Of particular interest are those planetary cases that straddle the radius boundary of being terrestrial or gaseous in nature, such as super-Earth and sub-Neptune exoplanets, respectively. The known exoplanet, TOI-2285 b, is one such case, since it lies at the radius boundary of super-Earth and sub-Neptune (Rp = 1.74 R circle plus), and receives a relatively high instellation flux since its orbit exists within both the Habitable Zone and Venus Zone (VZ). Here, we present an analysis of the planetary interior and climate to determine possible evolutionary pathways for the planet. We provide volatile inventory estimates in terms of the planet's bulk density and interior composition. We performed climate simulations using ROCKE-3D that provide a suite of possible temperate scenarios for the planet for a range of topographical and initial surface water assumptions. Using the outputs of the climate simulations, we modeled JWST transmission and emission spectroscopy for each scenario. Our results demonstrate that there are temperate scenarios consistent with the known planetary properties, despite the planet's estimated steam atmosphere and its location relative to the VZ.

Obliquity can shape the habitability of a planet by changing the seasonal availability of incident solar radiation. Changes in incident radiation can lead to changes in the availability of light, temperature, ocean circulation, stratification, and corresponding nutrient availability, all of which are important in determining ocean net primary productivity (NPP). Moreover, a fraction of the carbon assimilated by phytoplankton is sequestered in the deep ocean. Therefore, changes in productivity can alter the distribution of CO2 between the ocean and atmosphere. In this study, we investigate the effects of obliquity on ocean NPP and the atmospheric CO2 concentration using ROCKE-3D fully coupled to the NASA GISS Ocean Biogeochemistry Model. We find sea surface temperature primarily controls the NPP response, with both properties reaching a maximum at an obliquity of 45 degrees. We find that the response of the seasonal amplitude of NPP to obliquity is controlled primarily by photosynthetically available radiation and secondarily by changes in nutrient availability. We also find that atmospheric CO2 increases in response to obliquity, with a minimum at 15 degrees and a maximum at 60 degrees. The obliquity-driven CO2 changes are controlled primarily by temperature-driven solubility changes, with circulation and biology either enhancing solubility-driven changes at low obliquities or acting against and partially offsetting solubility-driven changes at higher obliquities. The magnitude of obliquity-driven changes is likely too small to be detectable, though future studies are needed to determine whether changing obliquity simultaneously with other orbital parameters can lead to larger, potentially detectable changes in NPP and CO2.