Sunday, March 20, 2011

Weather on Titan: New Season, New Knowledge

"On Saturn's Moon Titan, Methane Rains on the Desert"
Denise Chow, (March 17, 2011)

"When photos showed a large patch near the equator of Titan mysteriously darken and then grow lighter within a couple of weeks, scientists knew something big was happening on Saturn's largest moon. But what they found was something they didn't expect: a methane rainstorm in a region of Titan thought to be covered by vast, arid dunes.

"While the large moon is known to have methane lakes at its north and south poles, scientists thought Titan's equatorial region was mostly dry, but the likely cause of the darkness was determined to be an outburst of clouds and methane rain - which suggests Titan's equator has a rainy season.

"The photos taken by NASA's Cassini spacecraft on Sept. 27, 2010, showed a decrease in brightness over an area measuring over 1,200 miles (2,000 kilometers) long and 62 miles (100 km) wide...."

A key word in the article, in the Lemming's opinion, is "suggests." Rain on that part of Titan isn't guesswork, though:

"...Turtle and her colleagues examined other explanations for the darkening seen in Cassini's images, including strong windstorms and volcanism. Through their analyses, however, the researchers found that the effects of possible windstorms and volcanism on Titan were not consistent with the changes observed over such a large area...."

At this point, it looks like Titan's weather systems are like Earth's - but not quite. There's a diagram that shows what seems to be a reasonable model for how Titan's weather works:

(P. Huey/Science © 2011 AAAS, via, used w/o permission)
"Cloudy with rain. Simplified global atmospheric circulation and precipitation pattern on Titan and Earth. Most precipitation occurs at the intertropical convergence zone, or ITCZ, where air ascends as a result of convergence of surface winds from the northern and southern directions. Titan's ITCZ was previously near the south pole (A) but is currently on its way to the north pole (B). The seasonal migration of the ITCZ on Earth is much smaller (C and D). This image appears in a Perspective by Tetsuya Tokano titled, 'Precipitation Climatology on Titan.'
"CREDIT: P. Huey/Science © 2011 AAAS"

Saturn, and Saturn's moon Titan, go around our sun once for every 29 trips Earth makes - which means that it's going to be a while before we get a full year's worth of seasonal data. The article notes that Cassini got the Saturn system in 2004 - so data from that probe covers about a quarter of the Saturn/Titan year.

Still, it's more than we knew before.

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