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Sodium and Potassium Signatures of Volcanic Satellites Orbiting Close-in Gas Giant Exoplanets

Status Report From: arXiv.org e-Print archive
Posted: Thursday, August 29, 2019

Apurva V. Oza, Robert E. Johnson, Emmanuel Lellouch, Carl Schmidt, Nick Schneider, Chenliang Huang, Diana Gamborino, Andrea Gebek, Aurelien Wyttenbach, Brice-Olivier Demory, Christoph Mordasini, Prabal Saxena, David Dubois, Arielle Moullet, Nicolas Thomas

(Submitted on 28 Aug 2019)

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 p≲1011. This tidal energy is focused into the satellite driving a ∼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 RJ) 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 49-b 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.

Comments: 23 pages, 5 figures, accepted to ApJ

Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

Cite as: arXiv:1908.10732 [astro-ph.EP] (or arXiv:1908.10732v1 [astro-ph.EP] for this version)

Submission history

From: Apurva Oza  

[v1] Wed, 28 Aug 2019 14:04:24 UTC (1,333 KB)

https://arxiv.org/abs/1908.10732

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