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

Oza, Apurva V.; Johnson, Robert E.; Lellouch, Emmanuel; Schmidt, Carl; Schneider, Nick; Huang, Chenliang; Gamborino, Diana; Gebek, Andrea; Wyttenbach, Aurelien; Demory, Brice-Olivier; Mordasini, Christoph; Saxena, Prabal; Dubois, David; Moullet, Arielle; Thomas, Nicolas (2019). Sodium and Potassium Signatures of Volcanic Satellites Orbiting Close-in Gas Giant Exoplanets. Astrophysical journal, 885(2), p. 168. Institute of Physics Publishing IOP 10.3847/1538-4357/ab40cc

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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 (KI) 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 Qp ≲ 10¹¹. This tidal energy is also focused into the satellite driving an ∼10 5±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 (∼1000RJ) 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.

Item Type:

Journal Article (Original Article)


08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences
10 Strategic Research Centers > Center for Space and Habitability (CSH)
08 Faculty of Science > Physics Institute
08 Faculty of Science > Physics Institute > NCCR PlanetS

UniBE Contributor:

Oza, Apurva Vikram; Gamborino Uzcanga, Diana; Demory, Brice-Olivier; Mordasini, Christoph and Thomas, Nicolas


500 Science > 520 Astronomy
600 Technology > 620 Engineering
500 Science > 530 Physics




Institute of Physics Publishing IOP




Dora Ursula Zimmerer

Date Deposited:

04 Feb 2020 15:33

Last Modified:

09 Feb 2020 02:46

Publisher DOI:





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