Puzzling signal on Saturn’s moon Rhea may finally be

An image from Cassini of Saturn's icy moon Rhea

A picture from Cassini of Saturn’s icy moon Rhea

NASA/JPL-Caltech/House Science Institute

A thriller on Saturn’s moon Rhea could have lastly been solved. When NASA’s Cassini spacecraft flew previous the planet’s second-largest moon earlier than the tip of its mission in 2017, it noticed a mysterious compound. It seems, that compound could also be hydrazine, which is usually utilized in rocket gas.

As Cassini flew previous Saturn’s moons, it examined the daylight bouncing off their surfaces to find out what they’re product of. On Rhea, in addition to a number of of the other moons, one thing on the floor absorbed a portion of that mild within the ultraviolet vary of the spectrum.


“We observed there was this dip within the spectrum and questioned what it was, however we speculated that it is likely to be some kind of water ice,” says Amanda Hendrix on the Planetary Science Institute in California. “We puzzled over what it’s for a very long time.”

She and her colleagues noticed how mild bounced off a number of compounds in laboratory experiments, and located two that appeared to match what Cassini noticed on Rhea: hydrazine and chlorine. Whereas both might be a match for Cassini’s observations, it’s onerous to give you a means for chlorine to be on Rhea’s floor, Hendrix says.

Hydrazine, however, might be made in reactions between chemical substances that we all know exist on the icy moon. It might additionally float over from the thick ambiance of the neighbouring moon Titan. Despite the fact that Cassini did use hydrazine as gas for its thrusters, these thrusters have been by no means fired close to Rhea, so the researchers are that it didn’t come from the spacecraft.

“This can be a potential rationalization for the characteristic on Rhea, however we nonetheless have work to do to determine why it happens on different moons,” says Hendrix. “This can be a clue to some course of that’s occurring in the entire Saturn system, and doubtless elsewhere as nicely.”

Journal reference: Science Advances, DOI: 10.1126/sciadv.aba5749

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