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A rocky extrasolar moon overflowing with lava could orbit a planet 550 light-years from Earth, discovered astronomers led by researchers from the University of Bern.
The volcanically active exomoon could be hidden in the WASP-49b exoplanet system, orbiting a giant planet in the discrete constellation of Lepus, under the brilliant constellation of Orion.
The researchers describe the exomoon as an "extreme" version of Jupiter's moon Io – the most volcanically active body in our own solar system. So, portray an exotic and dangerous world – an 'exo-Io'.
Apurva Oza, postdoctoral fellow at the Institute of Physics at the University of Bern and partner of the PRN PlanetS, describes the exooon by comparing it to a famous science-fiction screenplay: "It would be a dangerous volcanic world with a surface of molten lava – a lunar version of nearby super-lands like 55 Cancri-e.
"A place where Jedis will die, dangerously familiar to Anakin Skywalker."
More than a grain of sodium. Combine theory and circumstantial evidence.
Astronomers have yet to discover a moon beyond our solar system, which means that researchers suspect the existence of this exo-Io of circumstantial evidence – namely the sodium gas contained in the WASP-49b at a unusually high altitude.
Oza explains, "The neutral sodium gas is so far away from the planet that it is unlikely that it is emitted solely by a planetary wind.
"Sodium is just where it should be."
The comparison of this feature with observations of the Jupiter and Io system with the help of low mass calculations demonstrated to the team that an exo-Io could actually constitute a plausible mechanism for sodium at WASP-49b.
Bob Johnson and Patrick Huggins have advanced the theory that large amounts of sodium around an exoplanet could indicate a hidden moon or ring of material in 2006. Next, researchers at the University of Virginia have calculated that a three-body system comprising a star, a nearby giant planet and a moon could remain stable for billions of years.
Oza relied on these theoretical predictions to form the basis of the work of himself and his colleagues – published in Astrophysical Journal.
The astrophysicist explains, "The huge tidal forces in such a system are the key to everything.
"The energy released by the tides on the planet and on its moon keeps the orbit of the moon stable, warming it and making it simultaneously volcanic."
The researchers also demonstrated in their study that a small rocky moon would eject more sodium and potassium into space via this extreme volcanism than a large gaseous planet. This would be particularly the case at high altitude.
These emissions can then be identified by astronomers using the technique of spectroscopy. These particular elements are particularly useful to astronomers.
Oza adds, "Sodium and potassium stripes are a treasure for us astronomers because they are extremely bright.
"The vintage street lights that illuminate our streets with yellow haze resemble the gas we now detect in the spectrum of a dozen exoplanets."
By comparing their calculations with actual observations of sodium and potassium, the team identified five candidate systems in which a hidden exomoon could survive thermal evaporation. In the case of WASP-49b, the best explanation of the data observed was the presence of an exo-Io.
This is not the only explanation, however. As mentioned above, high altitude sodium observations might instead indicate that the exoplanet is surrounded by a ring of matter – most likely an ionized gas.
Oza admits that the team needs to find more clues and, as such, relies on future observations with telescopes on the ground and in space. In addition, as some of these exo-Ios could possibly be destroyed as a result of extreme mass loss, the team also wants to look for evidence of such destruction.
Oza concludes, "While the current wave of research is moving toward habitability and biosignatures, our signature is a signature of destruction.
"The interesting part is that we can monitor these destructive processes in real time, like fireworks."
Original search: https://arxiv.org/pdf/1908.10732.pdf
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