Using the ESPRESSO instrument on ESO’s Very Large Telescope and the HARPS instrument at ESO’s La Silla 3.6-m telescope, astronomers have detected a sodium cloud close to but slightly out of sync with the hot, Saturn-sized gas-giant exoplanet WASP-49Ab.
This artist’s concept depicts a potential volcanic exomoon between WASP-49Ab (left) and its parent star. Image credit: NASA / JPL / Caltech.
WASP-49A is a faint Sun-like star discovered by the Wide Angle Search for Planets (WASP) in 2006.
Also known as 2MASS 06042146-1657550, the star is located approximately 635 light-years away from Earth in the constellation of Lepus.
Its transiting Saturn-mass companion, WASP-49Ab (also known as WASP-49b), was discovered in a 2.8-day orbit in 2012.
“Both WASP-49Ab and its star are composed mostly of hydrogen and helium, with trace amounts of sodium,” said Caltech astronomer Apurva Oza.
“Neither contains enough sodium to account for the cloud, which appears to be coming from a source that is producing roughly 100,000 kg of sodium per second.”
“Even if the star or planet could produce that much sodium, it’s unclear what mechanism could eject it into space.”
Dr. Oza and colleagues found several pieces of evidence that suggest the cloud is created by a separate body orbiting WASP-49Ab, though additional research is needed to confirm the cloud’s behavior.
For example, twice their observations indicated the cloud suddenly increased in size, as if being refueled, when it was not next to the planet.
They also observed the cloud moving faster than the planet in a way that would seem impossible unless it was being generated by another body moving independent of, and faster, than the planet.
“We think this is a really critical piece of evidence,” Dr. Oza said.
“The cloud is moving in the opposite direction that physics tells us it should be going if it were part of the planet’s atmosphere.”
The astronomers established that the cloud is located high above the planet’s atmosphere, much like the cloud of gas Io produces around Jupiter.
They also used a computer model to illustrate the exomoon scenario and compare it to the data.
WASP-49Ab orbits the star every 2.8 days with clocklike regularity, but the cloud appeared and disappeared behind the star or behind the planet at seemingly irregular intervals.
Using their model, the researchers showed that an exomoon with an eight-hour orbit around the planet could explain the cloud’s motion and activity, including the way it sometimes seemed to move in front of the planet and did not seem to be associated with a particular region of the planet.
“The evidence is very compelling that something other than the planet and star are producing this cloud,” said Dr. Rosaly Lopes, a planetary geologist at NASA’s Jet Propulsion Laboratory.
“Detecting an exomoon would be quite extraordinary, and because of Io, we know that a volcanic exomoon is possible.”
The findings were published in the Astrophysical Journal Letters.
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Apurva V. Oza et al. 2024. Redshifted Sodium Transient near Exoplanet Transit. ApJL 973, L53; doi: 10.3847/2041-8213/ad6b29
Source : Breaking Science News