Alkaline Signatures of an Active Exomoon
Abstract
Exomoons are generally too small to be detected by nominal searches. By analogy to the most active body in the Solar System, Io, we describe how sodium (Na I) and potassium (K I) gas could be a signature of the geological activity venting from an otherwise hidden exo-Io. Analyzing a dozen close-in gas giants hosting robust alkaline detections, we show that an Io-sized exomoon can be stable against orbital decay below a planetary tidal Qp < 1011. This tidal energy is focused into the satellite driving 105 times more mass loss than Io's supply to Jupiter's Na exosphere, based on a simple atmospheric loss model. The remarkable consequence is that several exo-Io column densities are on average more than sufficient to provide the 1010±1Na cm-2 required by the equivalent width of exoplanet transmission spectra. Furthermore, the benchmark observations of both Jupiter's extended ( 1000 RJ) Na exosphere and Jupiter's atmosphere in transmission spectroscopy yield similar Na columns that are purely exogenic in nature. As a proof of concept, we fit the "high-altitude" Na at WASP 49-b with an ionization-limited cloud identical to the precise Na profile about Io. Moving forward, we strongly encourage time-dependent ingress and egress monitoring along with spectroscopic searches for other volcanic volatiles.
- Publication:
-
AAS/Division for Extreme Solar Systems Abstracts
- Pub Date:
- August 2019
- Bibcode:
- 2019ESS.....430605O