Exoplanet atmospheres evolve under the influence of stellar radiation that heats, ionizes, and chemically alters gaseous envelopes. Sara Seager at Massachusetts Institute of Technology and James Kasting at Pennsylvania State University have emphasized that extreme ultraviolet and X-ray flux from host stars deposit energy high in atmospheres, driving thermal expansion and enhanced escape. Observations by the Space Telescope Science Institute using the Hubble Space Telescope and follow-up characterization by the James Webb Space Telescope under NASA programs provide empirical constraints on composition and mass loss, while models developed at the European Space Agency integrate those constraints into population-wide predictions.
Stellar radiation and escape mechanisms
Thermal escape processes include Jeans escape for light atoms and hydrodynamic escape when high-energy irradiation causes bulk outflow, a mechanism described in work by James E. Owen at University of Cambridge. Non-thermal processes such as ion sputtering, charge exchange, and pick-up by stellar winds are documented by researchers involved with the MAVEN mission led by Bruce Jakosky at University of Colorado Boulder and NASA, which measured ion losses from Mars and demonstrated how solar wind interactions can erode atmospheres in the absence of global magnetic shielding. Photochemistry driven by ultraviolet photons alters molecular reservoirs and can create secondary species that either escape more readily or lead to surface deposition, as detailed in atmospheric chemistry studies from David Catling at University of Washington.
Long-term consequences and habitability
Long-term outcomes depend on stellar type, planetary mass, and magnetic protection. Low-mass planets close to active M-dwarf stars, where flare-driven high-energy flux persists, are particularly vulnerable to substantial volatile loss according to analyses by Victoria Meadows at University of Washington, potentially stripping primary hydrogen envelopes or desiccating secondary atmospheres. Comparative planetology grounded in Martian studies shows cultural and environmental relevance: the loss of Mars's thicker early atmosphere, evidenced by MAVEN measurements and interpretations by Bruce Jakosky at University of Colorado Boulder, transformed its territorial habitability and informs planning for future human missions.
Implications for discovery and theory point to multi-wavelength monitoring and coupled interior-atmosphere models supported by NASA and the European Space Agency. Ongoing collaborations between observational teams at the Space Telescope Science Institute and theorists such as Sara Seager at Massachusetts Institute of Technology and James E. Owen at University of Cambridge continue to refine predictions of which planets retain thick atmospheres, which evolve toward thin, airless states, and which environments might preserve conditions relevant to life.
