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In the dark, chilly tropics of Saturn’s moon Titan, the Cassini probe has spotted what appears to be a lake of liquid methane, fueling speculation that caverns below might harbor life.
Titan has a rocky, icy surface coated by a thick atmosphere of nitrogen and methane. It’s a geologically-young moon, but below its dense atmosphere the surface is dotted by mountains and several possible cryovolcanoes, which are thought to erupt methane rather than magma.
It’s the only extraterrestrial object to have even shown clear evidence of stable bodies of surface liquid — in Titan’s case, methane — but these lakes of hydrocarbon have previously only been spotted in the planet’s polar regions. In 2009, exo-meteorologists saw evidence of weather on Titan, and since then the moon has been found to have a methane cycle rather like the water cycle on Earth — where methane evaporates and then rains down as a liquid elsewhere.
However, the discovery of the liquid methane lake in the desert-like tropical regions of the planet might throw a spanner into the works — any surface liquid there should evaporate and be transported to the cooler poles. “Lakes at the poles are easy to explain, but lakes in the tropics are not,” Caitlin Griffith, a planetary scientist at the University of Arizona in Tucson, told.
The lake that Griffith and her colleagues found is 37 miles long, 25 miles wide and at least 3.3 feet deep. It was persistent through observations between 2004 and 2008, and appears as a black mark on near-infrared wavelengths (which can penetrate Titan’s thick atmosphere). The team also found several smaller, brighter marks, which they believe may be “shallower ponds similar to marshes on Earth, with knee-to-ankle-level depths”.
So where is that methane coming from? One potential source could be below the surface. The researchers believe that subsurface oases of liquid methane could be replenishing these lakes as they evaporate from above. If that’s the case, it adds to the number of places where life could be found on Titan.
Of course it’s entirely plausible that it might not be a lake at all. A solid organic compound on the surface could also show up dark at these wavelengths. So far, only 17 percent of the moon’s equatorial regions have been analyzed at a resolution capable of spotting features of this size, but lower-resolution scans don’t indicate that tropical lakes are widespread.
A NASA mission to Titan to look at its complex chemistry in more detail, named the Titan Mare Explorer, has been proposed. It would spend three months in a sea of methane on the moon’s north polar region, measuring its composition with a mass spectrometer. NASA will decide soon on its fate.
Titan has a rocky, icy surface coated by a thick atmosphere of nitrogen and methane. It’s a geologically-young moon, but below its dense atmosphere the surface is dotted by mountains and several possible cryovolcanoes, which are thought to erupt methane rather than magma.
It’s the only extraterrestrial object to have even shown clear evidence of stable bodies of surface liquid — in Titan’s case, methane — but these lakes of hydrocarbon have previously only been spotted in the planet’s polar regions. In 2009, exo-meteorologists saw evidence of weather on Titan, and since then the moon has been found to have a methane cycle rather like the water cycle on Earth — where methane evaporates and then rains down as a liquid elsewhere.
However, the discovery of the liquid methane lake in the desert-like tropical regions of the planet might throw a spanner into the works — any surface liquid there should evaporate and be transported to the cooler poles. “Lakes at the poles are easy to explain, but lakes in the tropics are not,” Caitlin Griffith, a planetary scientist at the University of Arizona in Tucson, told.
The lake that Griffith and her colleagues found is 37 miles long, 25 miles wide and at least 3.3 feet deep. It was persistent through observations between 2004 and 2008, and appears as a black mark on near-infrared wavelengths (which can penetrate Titan’s thick atmosphere). The team also found several smaller, brighter marks, which they believe may be “shallower ponds similar to marshes on Earth, with knee-to-ankle-level depths”.
So where is that methane coming from? One potential source could be below the surface. The researchers believe that subsurface oases of liquid methane could be replenishing these lakes as they evaporate from above. If that’s the case, it adds to the number of places where life could be found on Titan.
Of course it’s entirely plausible that it might not be a lake at all. A solid organic compound on the surface could also show up dark at these wavelengths. So far, only 17 percent of the moon’s equatorial regions have been analyzed at a resolution capable of spotting features of this size, but lower-resolution scans don’t indicate that tropical lakes are widespread.
A NASA mission to Titan to look at its complex chemistry in more detail, named the Titan Mare Explorer, has been proposed. It would spend three months in a sea of methane on the moon’s north polar region, measuring its composition with a mass spectrometer. NASA will decide soon on its fate.
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