Japanese researchers using the Atacama Large Millimeter/submillimeter Array have found that galactic cosmic rays affect Titan’s atmosphere.

A team of Japanese researchers has found that cosmic rays from beyond the solar system affect the chemical reactions involved in the formation of nitrogen-bearing organic molecules in Titan’s atmosphere, the largest moon of Saturn.

This is the first time astronomers observe such processes. And that changes our understanding of Titan’s environment.

So the moon has a pretty unique atmosphere and it’s very attractive to us. That is because it has a number of organic molecules that form a prebiotic environment.

Titan has a chemical make-up that may be similar to Earth’s primordial atmosphere.

Saturn’s largest moon is the only planetary body in the Solar System, besides Earth, where rainfall and seasonally flowing liquids erode the landscape.

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However, in a new study, University of Tokyo’s Dr. Takahiro Iino and colleagues used Atacama Large Millimeter/submillimeter Array (ALMA) to study the chemical processes in Titan’s atmosphere. They found faint but firm signals of acetonitrile (CH3CN) and its rare isotopomer CH3C15N in the ALMA data.

“We found that the abundance of 14N in acetonitrile is higher than those in other nitrogen-bearing species such as HCN and H3CN,” says Iino. “It well matches the recent computer simulation of chemical processes with high energy cosmic rays.”

Two key players in the chemical processes of the atmosphere are ultraviolet (UV) light from the Sun and cosmic rays from beyond the Solar System.

“In the upper atmosphere, UV light selectively destroys nitrogen molecules containing 15N because the UV light with the specific wavelength that interacts with 14N is easily absorbed at that altitude,” the study authors explained.

“Thus, nitrogen-bearing species produced at that altitude tend to exhibit a high abundance of 15N.”

“On the other hand, cosmic rays penetrate deeper and interact with nitrogen molecules containing 14N.”

“As a result, there is a difference in the abundance of molecules with 14N and 15N.”

The team revealed that acetonitrile in the stratosphere is more abundant in 14N than those of other previously measured nitrogen-bearing molecules.

“We suppose that galactic cosmic rays play an important role in the atmospheres of other solar system bodies,” said Dr. Hideo Sagawa, a researcher at Kyoto Sangyo University.

“The process could be universal, so understanding the role of cosmic rays in Titan is crucial in overall planetary science.”

The researchers published their observation results in the Astrophysical Journal in February 2019.

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