Hydrogen escape has played a major role in sculpting the atmospheres of the terrestrial planets, with the most notable examples being the dessication of Venus and Mars. Because it can so greatly influence the composition of terrestrial planet atmospheres with time, it is important to understand the dynamics and escape of hydrogen in general, across solar system objects and in exoplanetary systems. Now is an opportune time to begin this synthesis, given near-continuous observation of Mars H escape by NASA’s MAVEN mission, Earth H escape by TWINS and other near-Earth assets, the discovery of H coronas around close-in exoplanets, and the complete H escape dataset from Venus Express at Venus. Beyond these observations, newly discovered phenomena that may control H escape from Mars and other planets are being explored with models, whose implications have not yet been fully integrated into observational studies or across objects. We will form an ISSI International Team to bring experts who study each of these topics together, combining experience to begin assembling a comprehensive framework for understanding H dynamics and escape across observed planets. In addition to observers, we will invite modelers of H escape to understand how the observations in hand should be interpreted, as well as how they can be used to inform studies of early Solar System escape and escape from exoplanets. The result of our team’s work will be a new understanding of hydrogen escape and atmospheric evolution in its cosmic context, at least one review article summarizing current knowledge of H escape, and greatly strengthened ties across disciplines and objects that will be essential to interpreting the planetary and exoplanetary data of tomorrow.

Read the submitted proposal [PDF]

Image credit: NASA & ESA