Researchers at NASA's Jet Propulsion Laboratory have identified a significant clue - a sodium cloud - that may indicate the existence of a volcanic moon orbiting the Saturn-sized gas giant exoplanet, WASP-49 b. Although further research is required to confirm the sodium cloud's origin, it appears to behave similarly to gas clouds formed by volcanic activity on Jupiter's moon Io.
Currently, no exomoons (moons orbiting planets outside our solar system) have been definitively identified, although several candidates have been proposed. One reason for the lack of confirmed discoveries may be that these moons are often too small and dim to be detected with current technology.
The sodium cloud around WASP-49 b was first discovered in 2017 and sparked the interest of Apurva Oza, who was then a postdoctoral researcher at JPL and is now a staff scientist at Caltech. Oza has spent years studying how volcanic activity from exomoons might be detected. For instance, Jupiter's moon Io regularly releases gases such as sulfur dioxide and sodium, forming vast clouds around the planet. Oza and his colleagues propose that a similar cloud might be detectable from another star system, even if the moon itself remains unseen.
Both the planet WASP-49 b and its host star are composed primarily of hydrogen and helium, with small amounts of sodium. However, the sodium cloud appears to originate from a source producing approximately 220,000 pounds (100,000 kilograms) of sodium per second. The researchers doubt the planet or star could produce that much sodium, and the mechanism by which such a cloud would be expelled into space remains unclear.
This has led to speculation that the source may be a volcanic exomoon. Oza's team has faced challenges in this research due to the great distance involved - planet, star, and cloud often appear as a single point of light in observations. To make progress, they studied the system over time.
A Cloud on the Move
A recent study published in 'Astrophysical Journal Letters' highlights several observations suggesting the cloud's origin is separate from the planet itself. In some instances, the cloud's size grew as if it was replenished when it wasn't near the planet. Moreover, the cloud's motion appeared faster than the planet's, a phenomenon that could only be explained by an independent, faster-moving object generating the cloud.
"We think this is a really critical piece of evidence," said Oza. "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."
However, more time is needed to observe and confirm the cloud's behavior, the researchers caution.
A Chance of Volcanic Clouds
To further investigate, the researchers utilized the European Southern Observatory's Very Large Telescope in Chile. Julia Seidel, a co-author of the study and research fellow at the observatory, established that the sodium cloud was located high above the planet's atmosphere, akin to the gas clouds surrounding Jupiter's moon Io.
Oza's team also developed a computer model to simulate the exomoon scenario and match it with their observations. While WASP-49 b orbits its star regularly every 2.8 days, the cloud appeared and disappeared behind the planet or star at irregular intervals. Their model suggests that a moon with an eight-hour orbit around the planet could explain this unpredictable movement.
"The evidence is very compelling that something other than the planet and star are producing this cloud," said Rosaly Lopes, a planetary geologist at JPL and co-author of the study. "Detecting an exomoon would be quite extraordinary, and because of Io, we know that a volcanic exomoon is possible."
A Violent End
Unlike Earth's volcanic activity, which is driven by internal heat, Io's volcanic activity is fueled by Jupiter's gravitational forces, which stretch and compress the moon as it orbits the planet. This tidal heating is responsible for Io's extreme volcanic nature.
If WASP-49 b hosts a similar-sized moon, the combination of rapid mass loss and the planet's gravitational pull could eventually cause the moon to disintegrate.
"If there really is a moon there, it will have a very destructive ending," said Oza.
Research Report:Redshifted Sodium Transient near Exoplanet Transit
Related Links
Jet Propulsion Laboratory
The million outer planets of a star called Sol
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