Abstract
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 . 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.
Highlights
OZA ET AL.K I have been detected in silicate (i.e. Io; Mercury; Moon) and icy (i.e. Europa; comets) bodies, but never in H/He envelopes such as the giant planet atmospheres of our Solar System
This pursuit was motivated by the recent evaluation of the uncertainties in the interpretation of the alkaline absorption features at hot Jupiters (Heng et al (2015); Heng (2016)) which has led to the suggestion described here, that an exogenic 1 source from an active satellite might not be unreasonable for certain hot Jupiters
The principal question which remains is how significant is the exogenic mass when compared to the expected endogenic mass, and is this additional mass already detected in the robust transmission spectra observations of Na I and K I? Nominal mass loss models from hot Jupiters estimate ∼ 107 kg/s of total mass corresponding to roughly ∼ 10 kg/s of Na for the nominal solar abundance scenarios whereas our exo-Io model can supply on the order of 4×106 kg/s of pure Na I, approaching the maximum volcanic output of Io and in effect, the possible destruction limit of an exo-Io
Summary
A large number of new transmission spectroscopy observations have detected this range of alkaline column densities which we will evaluate individually in this work This pursuit was motivated by the recent evaluation of the uncertainties in the interpretation of the alkaline absorption features at hot Jupiters (Heng et al (2015); Heng (2016)) which has led to the suggestion described here, that an exogenic 1 source from an active satellite might not be unreasonable for certain hot Jupiters. We provide order of magnitude predictions on additional signatures which could more conclusively confirm the first exo-Io
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