Abstract: Jupiter’s innermost Galilean satellite Io is the most volcanic body in the solar system, orbiting at ~6 Jovian radii. The subsequent Europa at ~9.6 Jovian radii also experiences tremendous tidal heating — melting its ice and possibly cryovolcanically venting saltwater into its exosphere. We present our latest exosphere simulations of Europa's neutral atmosphere as a prediction for Europa Clipper's MASPEX. Europa’s sodium & potassium (Na/K) exosphere is sputtered from its brine-rich surface forming a patchy sodium torus directly linked to its sputtering, and possibly, outgassing of its oceanic interior, conducive to life. Equipped with in-situ and remote observations of volcanic & ocean worlds in the solar system, along with the technique of evaporative transmission spectroscopy, we may now be able to indirectly probe small, rocky exomoons (e.g. Exo-Ios) via their volcanic gas signatures, light-years away. Analytically, the gravitationally and thermally-driven evaporation of exomoons has been able to reproduce the line-of-sight column densities of Na & K, regularly observed at ~dozens of transiting gas giant exoplanets. Here, we present new simulations of exomoon candidates, modeling their toroidal and cloud geometries in time, as well as their evaporative transmission spectra. Especially compelling exomoon candidates currently showcase spectral disappearances of Na&K at select systems, meriting follow-up by high-resolution and space-based spectrographs onboard HST/JWST. Lastly, we discuss the implications of an Io sample return mission concept, and its ability to ground-truth exoplanet-exomoon observations in the 2030s and beyond.

About the speaker: Apurva Oza is an astronomer & planetary scientist specializing in the physics and observations of exospheres in the solar system and beyond. The interdisciplinary nature of remotely observing tenuous gas also includes the study of tidal heating, volcanic processes, and their escape (e.g. Jupiter’s Io), along with charged particles and their ability to produce and sustain near-surface O2/H2O atmospheres on ocean worlds (e.g. Europa/Ganymede). These tidally-locked moons are ideal testbeds for close-in exoplanets, and tantalizingly hidden exomoons. Oza studied at UNC & UVA and holds a PhD from the Observatoire de Paris (Sorbonne). Oza was a postdoc at the University of Bern prior to daring mighty things(!) at JPL.