Thursday, August 20, 2009


Saturn’s largest moon (the solar system’s second largest moon), Titan, was discovered in 1655 by Dutch astronomer Christiaan Huygens. In 1944, Gerard Kuiper demonstrated that Titan’s dense atmosphere has the spectral signature of methane. Up until the arrival of the voyager 1 in 1980 and Cassini-Huygens in 2004, Titan was somewhat of a mystery with its surface features hidden beneath thick layers of clouds and haze.

Although the surface was still hidden, Voyager was able to learn much about the moon’s planet-like atmosphere. Titan’s huge atmosphere creates a surface pressure of 1.5 bars, a temperature of 94K, and a density of 5.3kg/m3. This surface temperature is close to the triple point of methane, which could mean that Titan has a methane cycle similar to Earth’s hydrological cycle.

In 2005, ESA’s Huygens Probe was released from Cassini and entered Titan’s atmosphere. It discovered that Titan and Earth’s atmosphere share a similar altitude/temperature relationship. On Earth, the temperature decreases with altitude in the troposphere, increases in the stratosphere due to the absorption of UV rays in the ozone, decreases in the mesosphere due to decreasing atmospheric density, and finally increases in the thermosphere due to the release of thermal energy caused by the breakup of molecules by solar radiation. On Titan, the temperature decreases with altitude in the troposphere, and increases in the stratosphere.

With several Cassini flybys, Titan’s mysterious surface is finally being revealed. Titan’s surface is incredibly Earth-like with rain-cut river beds, hydrocarbon lakes, and giant equatorial sand dunes. Much is still unknown about the surface, such as the depth of the lakes, and how the sand dunes are formed. Cassini Radar observations also confirmed that the entire crust of Titan is floating on top of a massive water ocean.

On April 2008 a large storm cell, approximately the size of India, was observed using the combined technologies of several observatories, such as NASA’S Infrared Telescope located on Mauna Kea in Hawaii. This storm was observed over a tropical region which would be a typical place for tropical storms to develop. More recently, a second large storm system was observed over a more arid region, where such storms are less expected to develop. These storms could be capable of producing large amounts of precipitation which would sculpt the moon’s surface, creating the surface geology which we are just beginning to see.

With a continuing Cassini mission, including 20 plus Titan fly-bys, there is definitely more discoveries to come. Titan is a moon well worth exploring with complex orbiters and robotic landers, not only for further observations of Titan’s exotic surface features, but also to look for signs of extremophiles. Any such mission will be expensive and several years into the future, so in the meantime we can enjoy the only sounds ever recorded on a body other than Earth. These sounds were recorded by the Huygens Probe as it descended through Titan’s atmosphere: Sounds of Titan�

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