Friday, October 12, 2007

Saturn's Weather Forecast: Methane Rain

Scientists have discovered that it can rain on Titan, Saturn's largest moon, and that the rain falls in the form of liquid methane. Yahoo News Reuters excerpt:

CHICAGO (Reuters) - The daily weather forecast on Saturn's largest moon Titan appears to be a steady drizzle of liquid methane, at least around the bright, exotically named region known as Xanadu, U.S. researchers said on Thursday.

But this is hardly the paradise romanticized by the Samuel Taylor Coleridge poem "Kubla Kahn."

New images from Hawaii's W.M. Keck Observatory and Chile's Very Large Telescope show nearly global cloud cover at high elevations and a dreary morning drizzle that seems to dissipate around midmorning local time -- which is about three Earth days after sunrise.

Scientists had expected rain in the atmosphere of this planet-sized moon, but these near-infrared images for the first time have revealed a persistent drizzle of methane off the western foothills of Xanadu.

"We expected that perhaps it was raining. It was reasonable that it could be raining. We just didn't know if it was raining right now," said Mate Adamkovics, a University of California, Berkeley researcher whose paper appears in the journal Science.

Titan is larger than the planet Mercury, but much, much colder, with surface temperatures of minus 297 degrees Fahrenheit (minus 183 degrees Celsius) -- cold enough to turn an explosive gas like methane into a liquid form.

"The question is, is it liquid methane that is sitting in a cloud, or is it falling through the sky," Adamkovics said in a telephone interview. His hunch is that it is falling, given the massive size of these raindrops, which Adamkovics believes are about 1,000 times bigger than rain on Earth.

"Because there is a bit less gravity and the atmosphere is thicker on Titan, the rain drops and the cloud drops are really big," he said. Whereas raindrops on Earth are micrometer sized, he said on Titan they appear to be a millimeter or bigger in size. "The droplet gets so big it can't hold itself together anymore," Adamkovics said.

I don't know about that. It rained like a bastard here for about two hours, and the raindrops I saw were a hell of a lot bigger than a millimeter, and they seemed to hold together quite nicely as they crashed into the roof of my wage-slavery containment facility. At least the rain has now stopped, and the skies have cleared, which means that the first game of the American League Championship series between the Red Sox and Indians at Fenway Park will at least be somewhat dry...

He and colleagues are now speculating about just what is causing the rain, and whether it follows weather patterns similar to those on Earth.

Xanadu, a region about the size of Australia, was first discovered in 1994 by NASA's Hubble Space Telescope.

I heard this story on NPR as I drove home, and it appears that there are also lakes of methane around this region. Some scientists think that Titan's environment is similar to models of early Earth, before outgassing occurred and the oceans formed. If this is true (or even if it is not), then we have a real life laboratory experiment just waiting to be conducted.

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