NASA spacecraft captures methane 'rain' on Saturn’s moon Titan

NASA's Cassini spacecraft has captured images of seasonal rains on Saturn's moon Titan — the first evidence of rain soaking Titan's surface at low latitudes.

Researchers at the University of Arizona's Lunar and Planetary Lab said the Titan's spring has brought showers of methane to its equatorial deserts.

"Titan continues to surprise and amaze us," said co-author Alfred McEwen.

"After years of dry weather in the tropics, an area the size of Arizona and New Mexico combined was darkened by methane rain over a period of just a few weeks," he added.

Extensive rain from large cloud systems, spotted by Cassini's cameras in late 2010, has apparently darkened the surface of the moon.

The best explanation is these areas remained wet after methane rainstorms.

The new findings show the weather systems of Titan's thick atmosphere and the changes wrought on the moon's surface are affected by the changing seasons.

"It's amazing to be watching such familiar activity as rainstorms and seasonal changes in weather patterns on a distant, icy satellite," said Elizabeth Turtle, lead author and a Cassini imaging team associate at the Johns Hopkins University Applied Physics Lab in Laurel, Md.

"These observations are helping us to understand how Titan works as a system, as well as similar processes on our own planet," she said.

The Saturn system experienced equinox, when the sun lies directly over a planet's equator and seasons change, in August 2009.

Years of Cassini observations suggested Titan's global atmospheric circulation pattern responds to the changes in solar illumination, influenced by the atmosphere and the surface, as detailed in the Geophysical Research Letters paper.

Cassini found the surface temperature responds more rapidly to sunlight changes than does the thick atmosphere. The changing circulation pattern produced clouds in Titan's equatorial region.

Clouds on Titan are formed of methane as part of an Earth-like cycle that uses methane instead of water. On Titan, methane fills lakes on the surface, saturates clouds in the atmosphere, and falls as rain.

Though there is evidence that liquids have flowed on the surface at Titan's equator in the past, liquid hydrocarbons, such as methane and ethane, had only been observed on the surface in lakes at polar latitudes.

These observations suggest that recent weather on Titan is similar to that over Earth's tropics. In tropical regions, Earth receives its most direct sunlight, creating a band of rising motion and rain clouds that encircle the planet.

The observations have been detailed in the journal Science.