Scientists Spot Massive Methane Rainstorm over Titan

Article excerpt

Worried about nasty tropical weather? Be glad you're not on Saturn's moon Titan.

Astronomers have discovered a storm system on Titan the size of India. It popped up in April 2008 in the moon's tropics, a latitude belt not known for cloudiness.

The storm, reported in the latest edition of the journal Nature, is another "a-ha" moment as scientists try to figure out how Titan's bizarre atmosphere works and the forces responsible for sculpting the moon's surface.

"These types of dramatic global weather events on Titan are rare and only last a few weeks," notes Henry Roe, an astronomer at the Lowell Observatory in Arizona and member of the team reporting the results.

The events suggested an atmosphere whose storm systems can significantly disturb Titan's equivalent of Earth's jet streams, triggering cloudiness elsewhere. It also helps explain why the surface in the tropics appears heavily sculpted by liquids despite the general dearth of clouds, the team suggests.

The European Space Agency's Huygens probe in 2004 returned pictures of what looked liked stream beds and other features seemingly carved by liquid on Titan's surface. Their structures implied they had formed under heavy downpours, much like what one sees in the US's desert Southwest.

An early Earth?

Indeed, the longer researchers stare at Titan, the more Earth- like its processes appear - processes playing out right before their telescopes' and spacecraft's sensors.

"It's really surprising how closely Titan's surface resembles Earth's," noted Rosaly Lopes, a planetary scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., at a recent meeting of the International Astronomical Union in Brazil. "Titan looks more like the Earth than any other body in the solar system, despite the huge differences in temperature and other environmental conditions."

Titan is bigger than Mercury. It's the only moon with a dense atmosphere - 98 percent nitrogen. And it's bitterly cold. The average temperature at the surface is -179 degrees Celsius (-290 degrees Fahrenheit). On Earth, water is a major sculpting agent. On Titan, water is frozen hard as a rock; the sculpting agent is liquid methane and ethane, which rains out of clouds composed of these hydrocarbons. …