Is there a volcanic exomoon orbiting this giant exoplanet?
- Are there moons in other planetary systems? There have been a growing number of tentative detections, but none confirmed yet.
- There is new evidence for a possible volcanic moon orbiting a giant planet 635 light-years away. The moon, if real, might be similar to Jupiter’s moon Io.
- An unusual cloud of sodium gas near the planet is best explained by a volcanic moon, NASA and Caltech astronomers said.
A volcanic exomoon like Io?
There are hundreds of known moons in our solar system, orbiting planets, dwarf planets and even asteroids. But what about in other planetary systems? We still don’t know for sure, although there have been some tentative detections (but not confirmed yet). Now, there may be new evidence for a moon – or exomoon – 635 light-years from Earth. NASA said on October 10, 2024, that there are possible signs of a volcanic exomoon – like Jupiter’s moon Io in our solar system – orbiting the Saturn-sized exoplanet WASP-49 b. The clues come from an unusual cloud of sodium close to the planet.
Researchers with NASA’s Jet Propulsion Laboratory and Caltech in California published their peer-reviewed findings in The Astrophysical Journal Letters on September 30, 2024.
The researchers had previously reported about the possible moon back in 2019 as well, but now the evidence seems to be even stronger.
An unusual sodium cloud
The researchers used the European Southern Observatory’s Very Large Telescope (VLT) in Chile for their observations. So how did they conclude there might be a moon orbiting WASP-49 b? The clues came from a cloud of sodium near the planet, first detected in 2017. How did it get there? The source – whatever it is – is producing about 220,000 pounds (100,000 kilograms) of sodium per second. Both the planet and its star contain only trace amounts of sodium, not nearly enough to account for the amount of sodium detected.
So where else could the sodium come from? The researchers, led by Apurva Oza, formerly at NASA’s Jet Propulsion Laboratory and now a staff scientist at Caltech, think it’s likely to be a moon orbiting the planet. If so, it could be similar to Jupiter’s volcanic moon Io. Io’s volcanoes release sulfur dioxide, sodium, potassium and other gases into space on a regular basis. They form diffuse clouds around Jupiter, up to an incredible 1,000 times Jupiter’s radius. Could the same thing be happening at WASP-49 b? The sodium cloud is also high above the planet’s atmosphere. This is similar to the gas cloud that Io’s volcanoes produce near Jupiter.
Is this a volcanic moon 635 light-years away? Video via NASA/ JPL-Caltech.
A volcanic exomoon for WASP-49?
In the new study, the researchers attempted to determine what the source of the sodium cloud might be. That was no easy task, given how far away the planet is from us at 635 light-years. As a result, it took a few years of observations of the WASP-49 system to come up with the best answer.
Those observations showed the sodium cloud was most likely coming from a body orbiting the planet, i.e., a moon. On two separate occasions the research team found the cloud increased in size when it was farthest from the planet. The cloud would appear and disappear behind the planet and the star at irregular intervals. The planet itself, however, always orbits its star every 2.8 days. The researchers used a computer model to try to figure out if a moon could be responsible. And indeed, they found a moon orbiting the planet about every eight hours would explain the data.
In addition, the cloud was moving faster than the planet itself. This also suggested that the cloud originated from a separate body. The moon would be moving faster in its orbit than the planet itself was moving. Also, the cloud was moving in the opposite direction than if it were somehow connected to the planet’s atmosphere. As Oza noted:
We think this is a really critical piece of evidence. 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.
Compelling evidence
Co-author Rosaly Lopes is a planetary geologist at the Jet Propulsion Laboratory. She said:
The evidence is very compelling that something other than the planet and star are producing this cloud. Detecting an exomoon would be quite extraordinary, and because of Io, we know that a volcanic exomoon is possible.
The researchers don’t know how large the exomoon may be. But they said that if it is similar in size to Earth’s moon (or smaller), then it will likely eventually disintegrate. This is from a combination of losing mass through its volcanoes and being squeezed by its planet’s gravity. The same thing happens on Io, where Jupiter’s immense gravity squeezes it when it is closest to the planet. It is that flexing that keeps Io hot and molten on the inside.
Other possible exomoons
Astronomers reported the first possible exomoon back in 2014. That one, if actually a moon, was orbiting a rogue, free-floating planet. In 2018, the Hubble Space Telescope (HST) tentatively discovered the first exomoon around a planet orbiting another star, Kepler-1625b. It would be much larger than any moons in our own solar system, however.
Numerous other possible exomoons have also been found in recent years, as EarthSky has reported on. The purported moon for WASP-49 b is just the latest, but certainly one of the most compelling.
Bottom line: Astronomers with NASA and Caltech have found that a volcanic exomoon may be producing a cloud of sodium gas near a giant exoplanet 635 light-years away.
Source: Redshifted Sodium Transient near Exoplanet Transit
Read more: Astronomers discover 6 possible new exomoons
Read more: 1st moon-forming disk around an exoplanet
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