Sodium and Potassium Signatures of Volcanic Satellites Orbiting Close-in Gas Giant Exoplanets
Abstract
Extrasolar satellites 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 satellite can be stable against orbital decay below a planetary tidal {{ \mathcal Q }}p≲ {10}11. This tidal energy is also focused into the satellite driving an ∼105±2 higher mass-loss rate than Io’s supply to Jupiter’s Na exosphere based on simple atmospheric loss estimates. The remarkable consequence is that several exo-Io column densities are, on average, more than sufficient to provide the ∼1010±1 Na cm-2 required by the equivalent width of exoplanet transmission spectra. Furthermore, the benchmark observations of both Jupiter’s extended (∼1000 R J) Na exosphere and Jupiter’s atmosphere in transmission spectroscopy yield similar Na column densities that are purely exogenic in nature. As a proof of concept, we fit the “high-altitude†Na at WASP-49b with an ionization-limited cloud similar to the observed Na profile about Io. Moving forward, we strongly encourage time-dependent ingress and egress monitoring along with spectroscopic searches for other volcanic volatiles.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- November 2019
- DOI:
- arXiv:
- arXiv:1908.10732
- Bibcode:
- 2019ApJ...885..168O
- Keywords:
-
- planets and satellites: atmospheres;
- planets and satellites: composition;
- planets and satellites: detection;
- planets and satellites: dynamical evolution and stability;
- planets and satellites: magnetic fields;
- planets and satellites: physical evolution;
- Astrophysics - Earth and Planetary Astrophysics;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 23 pages, 5 figures, accepted to ApJ