Liquid methane has been raining down on Titan, say NASA scientists, who have observed the equatorial weather on Saturn's largest moon for the first time.
Spring showers are currently soaking Titan's equatorial deserts, images captured by NASA’s Cassini spacecraft show. The pictures show a darkening of the surface of the moon, most easily explained as wet areas after methane rainstorms.
"It's amazing to be watching such familiar activity as rainstorms and seasonal changes in weather patterns on a distant, icy satellite," says imaging team associate Elizabeth Turtleat. "These observations are helping us to understand how Titan works as a system, as well as similar processes on our own planet."
Clouds on Titan are formed of methane in the same way as Earth's water-based clouds. Methane fills lakes on the surface, saturates clouds in the atmosphere, and falls as rain.
Though liquids do appear to have flowed on the surface at Titan's equator in the past, liquid hydrocarbons, such as methane and ethane, had only been seen on the surface in lakes at polar latitudes.
Scientists suspected that clouds might appear at Titan's equatorial latitudes as spring in the northern hemisphere progressed. But they weren't sure if dry channels previously observed were cut by seasonal rains or remained from an earlier, wetter climate.
The new observations suggest that recent weather on Titan is similar to that over Earth’s tropics, where most direct sunlight falls and creates a band of rising motion and rain clouds that encircle the planet.
"These outbreaks may be the Titan equivalent of what creates Earth's tropical rainforest climates, even though the delayed reaction to the change of seasons and the apparently sudden shift is more reminiscent of Earth's behavior over the tropical oceans than over tropical land areas," says team member Tony Del Genio.