Titan's Lakes Are a Gas
LIANE HANSEN, host:
An astronomical first late last month. Scientists announced that they have found lakes on an object in our solar system other than the Earth. But before you pack your bags for a summer vacation, beware, you are not likely to get a suntan on Saturn's moon, Titan. And the lakes aren't water, they're essentially liquefied natural gas.
NPR's Richard Harris reports.
RICHARD HARRIS reporting:
Astronomers had long suspected that Titan would be swathed in whole oceans of liquid natural gas that is a mix of methane and ethane. So 18 months ago, when the Huygens space probe actually parachuted down to the surface, scientists like Larry Soderblom from the U.S. Geological Survey were anxious to learn the truth.
Mr. LARRY SODERBLOM (U.S. Geological Survey): We sort of had three landing scenarios. One was splash, one was thud, and the other was crash tinkle-tinkle.
HARRIS: Huygens landed with a thud on dry ground, but Soderblom and his colleagues didn't give up on the idea of finding liquid on the surface. Huygens was a one shot deal, but it had been delivered to Titan by the Cassini space probe, and Cassini finally turned its cloud-penetrating radar to get a close-up of Titan's north pole.
Jonathan Lunine from the University of Arizona flew to the Jet Propulsion Lab in Pasadena to see what this radar image would reveal.
Mr. JONATHAN LUNINE (University of Arizona): And when it came up on the screen, there in the center was Minnesota, is basically all I can say, just lakes everywhere at the high latitudes, and a very, very beautiful image.
HARRIS: The Minnesota Office of Tourism need not worry about losing visitors to Titan, though. Not only are the lakes on Titan a bit out of the way...
Mr. LONEAN: They're not swimmable unless you like swimming in liquid methane at a temperature of minus 290 Fahrenheit or minus 180 Celsius.
HARRIS: That's cold enough to make methane or natural gas a liquid. The lakes appear to be a critical link in the mysterious cycle of methane on Titan. It essentially plays the same role water plays on Earth, as bodies of liquid, as rainfall, and as an agent that sculpts the landscape through erosion.
Larry Soderblom says these lakes cover less than one percent of the moon, but they hint that there's a great deal of liquid methane lurking just below the surface.
Mr. SODERBLOM: It looks almost like a big slop in which a flood has risen. And you see outliers of little lakes scattered all around larger lakes, and they could be connected through the sub-surface sort of water table, methane table.
HARRIS: These scientists suspect that the lakes gradually evaporate, and by so doing bring methane into the atmosphere. It probably takes centuries to build up enough methane in the atmosphere to cause a really good downpour. But Jonathan Lunine says the deep channels gouged into the surface suggest that Titan must at times have gushing liquid on the surface.
Mr. LUNINE: These heavy methane thunderstorms that are occasional may in fact be the way that these streams and river channels are carved on Titan.
HARRIS: So this other worldly place turns out to have weather like the Earth, river channels, dunes, volcanoes, rocks - only made of water ice instead of granite - and now lakes. Larry Soderblom can hardly believe it.
Mr. SODERBLOM: It's amazing that a place so alien in its chemistry and environment and temperature could look more like the Earth than anything else we've come to see.
HARRIS: And more surprises are no doubt in store. Cassini will be stepping up its observation of Titan later this year.
Richard Harris, NPR News.