Saturn's Moon, Titan, Has Earth-like Polar Winds that Whip Gas into Space

Saturn's moon, Titan, may have an atmosphere that's far more Earth-like than once thought. Researchers have discovered that the moon has polar winds that drives gas from its atmosphere into space.

Titan is a remarkable body in our solar system. Like Earth and Venus, it has a rocky surface and a thick atmosphere. In fact, it's the only object in the solar system, besides Earth, to have rivers, rainfall and seas. Because of these features, Titan is the most studied moon other than Earth's.

"Titan's atmosphere is made up mainly of nitrogen and methane, with 50 percent higher pressure at its surface than on Earth," said Andrew Coates, one of the researchers, in a news release. "Data from CAPS proved a few years ago that the top of Titan's atmosphere is losing about seven tons of hydrocarbons and nitriles every day, but didn't explain why this was happening. Our new study provides evidence for why this is happening."

Hydrocarbons are a category of molecules that includes methane, as well as other familiar substances including petrol, natural gas and bitumen. Nitriles are molecules with nitrogen and carbon tightly bound together.

In this latest study, the researchers discovered that atmospheric loss is actually driven by a polar wind powered by an interaction between sunlight, the solar magnetic field and the molecules present in the upper atmosphere.

"Although Titan is ten times further from the sun than Earth is, its upper atmosphere is still bathed in light," said Coates. "When the light hits the molecules in Titan's ionosphere, it ejects negatively charged electrons out of the hydrocarbon and nitrile molecules, leaving a positively charged particle behind. These electrons, known as photoelectrons, have a very specific energy of 24.1 electronvolts, which means they can be traced by the CAPS instrument, and easily distinguished from other electrons, as they propagate through the surrounding magnetic field."

Titan doesn't have a magnetic field. However, it's surrounded by Saturn's rapidly rotating magnetic field. Negatively-charged photoelectrons, in turn, set up an electric field around Titan. The electrical field, in turn, is strong enough to pull the positively charged hydrocarbon and nitrile particles from the atmosphere throughout the sunlit portion of the atmosphere, setting up the widespread "polar wind" that scientists have now seen. This phenomenon has only been seen on Earth before now.

The findings reveal a bit more about Titan, and show that this moon is far more like Earth than previously thought. This, in turn, shows that the moon may actually be one of the most Earth-like worlds ever studied.

The findings are published in the journal Geophysical Research Letters.

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