Thirteen years ago, the Cassini-Huygens spacecraft orbited Saturn, not yet on its first mission, when a set of telescopes on board observed an unknown ultraviolet signal. Although the intriguing data was recently inspected, an international research team suspects it could indicate the presence of hydrazine on Saturn’s second largest moon, Rea.
The effort, which includes scientists from the UK, Taiwan, India and the US, used spectral data provided by UVIS, a giant telescopic that looked a bit like a refrigerator turned around. (UVIS was much more technologically complex than a refrigerator and it was destroyed along with the rest of Cassini in 2017, when the vessel fell into Saturn’s atmosphere.) Taken during Rea’s flybys in 2007 and 2011, the data Cassini collected indicated an unidentified spectroscopic signature emanating of the icy moon. In other words, something in Rea was reabsorbing the ultraviolet radiation and the team was trying to figure out which molecule was responsible. Their findings are published today in the journal Science Advances.
“The possible detection of hydrazine monohydrate in the Saturnian system (Rea) is significant as it may point to the presence of ammonia in the ice layers of Saturn’s icy moons,” said Mark Elowitz, an astrophysicist at the Open University of Saturn. United Kingdom. the author of the document said in an email. “Ammonia is important because it could depress the freezing point of water-ice mixtures, thus increasing the likelihood that underground oceans may exist inside some of Saturn’s icy satellites.”
The recent research effort was based on Elowitz’s dissertation, which also explored the reflectance spectra of the moon Dione, another of Saturn’s 82 odd moons, although this analysis is not included in the recent document. It is worth noting that Cassini used hydrazine fuel to propel it through space, which means it is possible that the spacecraft detected its own escape. The team doesn’t believe this happened, as Rhea’s flybys were not powered by hydrazine propellers, which were not firing at the time.
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Although hydrazine seems to be the most likely culprit in the absorption band, one alternative explanation is a kabbalah of chlorine-containing compounds. Hydrazine makes a little more sense, as it would be produced more easily, chemically speaking, than chlorine chemicals, “which would require the presence of an internal ocean in Rea,” Elowitz said.
In either scenario, there is evidence that serious organic chemistry is occurring in the outer solar system. Some astrobiologists believe that two of Saturn’s moons, Enceladus i Tità, could even contain alien life.
“The presence of hydrazine is an indication that the surfaces of icy satellites act as chemical factories in the manufacture of complex molecules, especially the biomolecule precursors needed for the origin of life.” Bhalamurugan Sivaraman, an astrochemist at the Physical Research Laboratory of India in Ahmedabad and co-author of the paper, said in an email.
Although the absorption band was detected in Rea, the team is not sure what caused it to originate from the moon. Around the bend is Titan, Saturn’s largest moon by far and the only moon in our solar system with a substantial atmosphere. The team argues that if hydrazine was not produced by chemical reactions between ammonia and water ice in Rea, it could have left Titan’s nitrogen-rich atmosphere and landed on the smaller moon.
“The idea that hydrazine may have formed in Titan’s atmosphere before it was transferred to Rea is a good reminder that the individual objects in the planetary systems — and the young stellar objects that precede them — do not exist in isolation. “, Olivia Harper Wilkins, an astrochemist at the California Institute of Technology who did not participate in the new research, said in an email. “I will be curious to see if NASA’s planned dragonfly mission will give us a better idea of whether hydrazine could originate on Titan and, if so, whether that hydrazine (or other molecules) could be transported to the other moons of Saturn “.
In fact, upcoming missions will deepen our understanding of the outer solar system. Unfortunately, we will have to wait until the 2030s for Dragonfly’s journey to Titan, which we hope will answer many of these questions and will surely raise many new ones.