As with most space probes, what is initially found is likely to be very outlier data whose signals are strong enough to be identified and fit only a limited range of explanations. This appears to be the case for WASP 49b. A paper on exoplanet atmospheres in 2017 reported the presence of a layer of sodium around a gas giant at unusual heights above the clouds.
Oza and his colleagues published a paper in 2019 arguing that the sodium was emitted not by an exoplanet, but by an exomoon similar to Io, Jupiter’s volcanic moon. We have already found volcanic planets; These planets were rocky worlds with prominent features such as orbital eccentricity, temperature distribution, or atmospheric features.
Gas giants cannot have volcanoes; Because the mountains are clearly rocky in nature. But a remaining possibility could be that the sodium effect seen on WASP 49b is the result of planetary activity such as planetary winds. Oza and his colleagues are still collecting data to confirm the previous findings and the possible external origin of this gas cloud.
Researchers used the European Southern Observatory’s Very Large Telescope to observe the star WASP 49 and its exoplanet for four nights. They already knew that this exoplanet has 0.37 times the mass of Jupiter and 1.1 times its radius and orbits its Sun-like star once every 2.8 days. When the researchers closely observed this system, they realized that the sodium cloud does not exist continuously; Rather, it comes and goes, disappearing behind its planet and star at regular intervals.
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Neutral sodium is photoionized in a few minutes; This means that it cannot survive in the vicinity of the star for a long time without acquiring an electric charge. Since the discovered sodium is neutral, its production must be constant and continuous.
One possible explanation is sodium production within the exoplanet; But the intervals during which the sodium cloud appeared were out of sync with the rotation of WASP 49b; This means that they cannot be linked to a place on an exoplanet.
Thanks to the relationship between Jupiter and Io, it is possible to explain how and why volcanic activity occurs on the exomoon. Perhaps this moon is being pushed and pulled as it orbits WASP 49b by gravitational tugs with it or other moons, such as Io’s interactions with Jupiter’s other Galilean moons.
The moon is also at a close distance from its planet; This means that in addition to mass reduction due to volcanic activity, its orbit probably deteriorates in relatively short time scales and eventually this path ends with the fall of the moon in WASP 49b. According to Uza, if there is really a moon around this planet, it will experience a fatal end.
The research findings have been published in Astrophysical Journal Letters.
