Once again, we are reporting on molecules in the atmosphere of a distant world. Instead of Venus or Titan, we’re talking about Saturn’s moon, Rhea. In a new report in Science Advances, a team of researchers claims to have found evidence of hydrazine. As always, we want to remind you all that this data comes from the amazing Cassini mission, which is the mission that keeps on giving despite ending years ago.

The team analyzed the ultraviolet spectroscopy of the moon’s atmosphere, and found a particular absorption feature that could be explained by either hydrazine or chlorine-containing compounds. And while hydrazine was a propellant used by Cassini, those thrusters were not used while observing the icy satellite flybys to prevent such contamination, so if the signal is from hydrazine, it’s not fuel from the spacecraft.

So how could hydrazine be formed on Rhea? That part is a bit unclear. Per the press release: The E-ring grains of Saturn could bombard and coat much of the surface of Rhea, and such bombardments from different sources could cause chemical changes in the irradiated surface to synthesize a rich surface chemistry.

In addition to that, the irradiation of ammonia by charged particles from Saturn’s magnetosphere induced the dissociation of ammonia molecules to form diazene and hydrazine.

But we haven’t really studied Rhea’s surface, so figuring out where the ammonia might come from is still a question to answer. More orbiters!

More Information

Phys.org article

“Possible detection of hydrazine on Saturn’s moon Rhea,” Mark Elowitz et al., 2021 January 22, Science Advances