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Giant storm helps brighten research on moon of Saturn


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POSTED: Thursday, August 13, 2009

Extraterrestrial storm trackers are reporting unusual activity on Saturn's moon Titan, so cold it rains liquid methane.

From telescopes on Mauna Kea, astronomers observed “;dramatic brightening”; from a huge storm covering nearly 1.2 million square miles—twice the size of Alaska, said Emily Schaller, formerly with the University of Hawaii Institute for Astronomy.

The observational coup in April last year capped three years of relatively mundane activity on Titan, where large clouds are rare in the dry mid latitudes.

Suddenly the moon “;put on quite a show,”; said Schaller, a former Hubble Fellow at the UH institute.

“;It was very boring most of the time,”; she said in a telephone interview from Arizona, where she moved two weeks ago as a Hubble Postdoctoral Fellow at the University of Arizona. “;Finally, after three years, we saw this huge event.”;

The astronomers were excited to catch the event, she said, explaining they probably would have missed it if they hadn't been observing every day with the NASA Infrared Telescope Facility and Gemini North telescope on Mauna Kea.

Their findings, “;Storms in the Tropics of Titan,”; were published today in the journal Nature. Schaller was first author. Others were H.G. Roe of Lowell Observatory, Tapio Schneider and M.E. Brown of the California Institute of Technology and UH astronomers Tobias Owen and Gareth Wynn-Williams.

Schaller said she has an ongoing program with the UH-managed NASA Infrared Telescope to monitor Titan almost nightly.

“;It's like getting a daily weather report for Titan,”; said Schaller, whose doctoral dissertation focused on the enigmatic moon, slightly larger than the planet Mercury.

If the spectrum shows clouds, the Gemini telescope is used to track them and identify the location.

“;The two programs enabled us to track these storms so well,”; Schaller said. “;We couldn't do one without the other.”;

Schaller said the storm occurred between two flybys of the Cassini orbiter, which passes Titan every six weeks. “;We were fortunate we were monitoring from the ground because Cassini basically missed the cloud activity.”;

Titan, with a diameter about 40 percent of Earth's, has a thick atmosphere and a weather cycle similar in many ways to Earth, with clouds and rain, Schaller said. But while 60 percent of Earth is covered with clouds most of the time, only about 1 percent of Titan ever has clouds, she said.

Of note was the storm's location, in Titan's tropical latitudes, generally the driest region, Schaller said. The event set off a chain of activity that lasted about a month, she said.

“;What we've shown is occasionally we can have large clouds over a desert-like region, which is not so dissimilar from Earth.”;

But it is so cold on Titan, minus 288 degrees Fahrenheit, that bedrock is not made up of rock but of frozen water, she said.

“;Rocks are being carved by flowing liquid methane. It is a very different system from what we have on Earth. A lot of people are doing laboratory experiments to understand the system.”;