Titanic Lakes
Published on Mar 19, 2007 at 10:06 pm.
1 Comment.
Filed under extraterrestrial moons.
Titan, Saturn’s largest moon, has long been suspected of harboring lakes, rivers, and seas. Titan has an atmosphere, and it is shrouded by a cloud of methane and other organic molecules. The temperature and pressure at Titan’s surface is very close to the triple point of methane (the main ingredient in natural gas).
A number of years ago, the Hubble Space Telescope showed indications 
of large areas that reflected light like methane. But, the real evidence started pouring in when the Cassini spacecraft arrived at Saturn in 2004. Cassini began using radar to map Titan beneath its clouds. These maps showed smooth regions, believed to be liquid pools, and what appear to be rivers. This is exciting, because it would be the first object in the Solar System other than Earth to conclusively have been shown to have liquid on its surface at this time.
Well, as exciting as this is, it turns out that some of the lakes on Titan are truly huge. At the top of this post, I have a NASA image showing a lake near the north pole of Titan that is compared to Lake Superior, with both images the same scale. JPL claims that a body this size (about 100,000 square kilometers) should be called a sea. That may or may not be the case. Normally, I think of a sea as being deep. It isn’t at all clear how deep these bodies of liquid are on Titan. They may be only a few feet deep, or they may be as deep as Lake Superior (though probably not likely). Also, there is no proof that these “lakes” on Titan are really liquid. At present, we are presuming that they are due to their smoothness and other secondary features that would be consistent with their being pools of liquid (probably methane).
In fact, with atmospheric conditions near methane’s triple point, Titan could have a whole rain cycle like on Earth. Methane might evaporate, then condense, and rain, running off in rivers and streams, collecting in great pools, and then evaporating again. But, all this is temporary. Ultraviolet light from the Sun is breaking down methane in the atmosphere. Perhaps “volcanic” eruptions and outgassing replenish the methane, but Titan likely has less than it used to. And, the Sun is gradually getting warmer. Eventually, Titan, which has not much more gravity than our own Moon, will warm to the point that it loses much of its atmosphere.
But, for now, it seems to quite possibly have methane lakes and rivers. If there are rivers, then there is no doubt methane rain.
-Astroprof
Images Courtesy of NASA, ESA
thirst4knowledge on May 19, 2008 at 8:05 am: 1
well if the sun gradually gets warmer then the methane will evaporate into the atmosphere.Methane we know is a heavy green house gas (much heavier than carbon dioxide) and could this methane gas push titan into a greeenhouse effect,warming the satelite to possibly be habitable to humans.