On Saturn’s Moon, It Rains Methane

Clouds of methane on Saturn’s moon Titan really aren’t clouds at all, but a steady rain of natural gas droplets, NASA and French researchers say.

Based on a new analysis of the Voyager 1 spacecraft’s November, 1979, flight past Titan, “We find that the methane clouds are composed of such large particles that they would be considered rain, not clouds, on Earth,” they said at last week’s American Geophysical Union meeting in San Francisco.

“It probably would be a constant rainfall,” said Regis Courtin, a French planetary scientist who led the study as a visitor to NASA’s Ames Research Center in Mountain View.

The methane forms directly into raindrops because Titan’s atmosphere lacks microscopic particles around which gases can condense into tiny vapor particles that make up clouds, the researchers said, adding that the methane condenses rapidly and directly into raindrops.

During its 1979 fly-by of Saturn’s largest moon, which measures about 3,200 miles across, Voyager 1 studied how infrared light from the sun was absorbed and re-emitted by the nitrogen, methane and hydrogen gas that makes up Titan’s atmosphere. Methane is present in the natural gas used to heat and cook on Earth.