Researchers discover an ice on the giant moon of Saturn

Rain, seas and an eroding surface of organic matter are found on Earth and Titan, the largest moon of Saturn. However, on Titan, it is the methane, not the water, which fills the lakes with drops of melting rain.

In searching for the source of Titan's methane, Caitlin Griffith, a researcher at the University of Arizona, and her team discovered something unexpected: a long line of ice that surrounds almost half of Titan.

Griffith, professor at the AU Lunar and Planetary Laboratory, is the lead author of the paper published today in Nature Astronomy.

On Titan, atmospheric methane molecules are continually broken by sunlight. The resulting atmospheric haze is deposited on the surface and accumulates as organic sediments, rapidly depleting atmospheric methane.

This organic veneer is composed of the material of past atmospheres.

There is no obvious source of methane except by evaporation of methane from polar lakes. But Titan's lakes contain only one-third of the methane in Titan's atmosphere and will soon be depleted by geological time scales.

According to one theory, methane could be supplied by underground reservoirs that release methane into the atmosphere. Previous studies on Titan indicate the presence of a singular region called Sotra, which looks like a cryo-volcano, with iced flow characteristics.

The Griffith team undertook to study the composition of Titan's surface, hoping in part to find subtle cryo-volcanic candidates. They analyzed half the surface of Titan and none was detected, but Sotra proved exceptional in that it exhibited the strongest ice characteristics.

Yet the main feature of ice found by the researchers was totally unexpected. It is a linear ice corridor that wraps around 40% of the circumference of Titan.

"This frozen corridor is confusing because it does not match any surface features or measurements of the subsoil," Griffith said. "Since our study and previous work indicates that Titan is not currently volcanically active, the corridor track is probably a remnant of the past, we detect this on steep slopes, but not on all slopes. is currently being eroded and could reveal the presence of ice and organic layers. "

The analysis of the team also indicates a diversity of organic matter in some areas. These surface deposits are interesting because the laboratory simulations of Titan's atmosphere produce biologically interesting compounds such as amino acids.

Griffith analyzed tens of thousands of spectral images taken with Cassini's visible and infrared mapping spectrometer, using a method to detect weak surface features.

This feat was accomplished by Griffith's application of Principal Component Analysis, or PCA. This allowed him to unravel the subtle traits caused by ice and organic sediments on the surface of Titan because of the omnipresent haze and its more obvious surface features. Instead of measuring the surface characteristics individually for each pixel in an image, the PCA uses all the pixels to recognize the main and more subtle signatures.

The Griffith team compared its findings with those of previous studies, including the Huygens probe, which landed on Titan in 2005. The comparison validated both the technique and the results. Plans are underway to use this technique to explore the poles where the methane seas are located.

"Titan and Earth have followed different pathways, and both have resulted in atmospheres and surfaces rich in unique organic materials," Griffth said. "But it's not clear if Titan and Earth are common patterns of body-rich organic matter or two among many worlds rich in organic matter."