A volcanically active rocky exomoon may orbit WASP-49b, a hot gas giant approximately 550 light-years away in the constellation of Lepus.
An artist’s impression of an exo-Io undergoing extreme mass loss. The hidden exomoon is enshrouded in an irradiated gas cloud shining in bright orange-yellow, as would be seen with a sodium filter. Patches of sodium clouds are seen to trail the lunar orbit, possibly driven by the gas giant’s magnetosphere. Image credit: Thibaut Roger / University of Bern.
“It would be a dangerous volcanic world with a molten surface of lava, a lunar version of close-in super-Earths like 55 Cancri e,” said Dr. Apurva Oza, a postdoctoral researcher at the University of Bern.
“The enormous tidal forces in such a system are the key to everything,” he added.
“The energy released by the tides to the planet and its moon keeps the moon’s orbit stable, simultaneously heating it up and making it volcanically active.”
In their work, Dr. Oza and colleagues were able to show that a small rocky moon can eject more sodium and potassium into space through extreme volcanism than a large gas planet, especially at high altitudes.
The researchers also compared their calculations with observations of several giant exoplanets and found five candidate systems where a hidden exomoon can survive against destructive thermal evaporation.
For WASP-49b, the observed data can be best explained by the existence of an exo-Io — an extrasolar version of Jupiter’s volcanic moon Io.
“The neutral sodium gas was detected at the WASP-49b at an anomalously high-altitude,” Dr. Oza and co-authors said.
“The sodium is so far away from the planet that it is unlikely to be emitted solely by a planetary wind.”
“Observations of Jupiter and Io in our Solar System, along with mass loss calculations, show that an exo-Io could be a very plausible source of sodium at WASP-49b. The sodium is right where it should be.”
However, there are other options. For example, WASP-49b could be surrounded by a ring of ionized gas, or non-thermal processes could be involved.
“We need to find more clues. We are relying on further observations with ground-based and space-based instruments,” Dr. Oza said.
“While the current wave of research is going towards habitability and biosignatures, our signature is a signature of destruction. A few of these worlds could be destroyed in a few billion years due to the extreme mass loss.”
“The exciting part is that we can monitor these destructive processes in real time, like fireworks.”
The team’s paper will be published in the Astrophysical Journal.
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Apurva V. Oza et al. 2019. Sodium and Potassium Signatures of Volcanic Satellites Orbiting Close-in Gas Giant Exoplanets. ApJ, in press; arXiv: 1908.10732
