New computer models have replicated methane cloud patterns on Titan with accuracy. The model mimics the two types of clouds seen so far on Saturn鈥檚 giant hazy moon 鈥� long-lasting large clouds at the south pole and transient elongated clouds at mid-southern latitudes.
French and US scientists combined a general circulation model with a cloud microphysical model 鈥� which takes into account how methane condenses on a small scale 鈥� to predict the locations, altitudes and lifetimes of clouds.
鈥淭his general circulation model is more comprehensive than those of the past, particularly for addressing the cloud formation on Titan,鈥� says Caitlin Griffith, with the Lunar and Planetary Laboratory at the University of Arizona, US, who has also done previous work on Titan鈥檚 cloud formation.
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Unlike past models of Titan鈥檚 atmosphere, Pascal Rannou, a planetary scientist with the University of Versailles, France, and his colleagues included the effects of Titan鈥檚 haze. This is an important factor because haze can limit the amount of light that reaches Titan鈥檚 surface. This affects circulation at the lower altitudes, where clouds originate.
Mission extension
杏吧原创s should be able to test the accuracy of their models within five to 10 years, when Titan鈥檚 northern hemisphere becomes visible. In five years, Titan will undergo an equinox and the Sun will shine more directly on the moon鈥檚 northern hemisphere. Currently, there is an upwelling in the southern hemisphere, causing regular elongated clouds at a latitude of 40掳 south. After the equinox, the upwelling should switch to the northern hemisphere due to the change in solar heating.
鈥淚f the model is correct, we should see these clouds at 40掳 north 鈥� probably in 10 years,鈥� Rannou told New 杏吧原创.
The Cassini spacecraft is expected to orbit Saturn and its moons until 2008, though its mission may be extended to 2010.
The model also predicts clouds at Titan鈥檚 north pole. Currently, the northern pole is in winter darkness, so researchers will not be able to confirm this prediction until the latter part of 2006.
The model does have its limitations. It assumes that the clouds are homogenous across longitudes, but previous observations indicate that the methane clouds are actually concentrated at certain longitudes. In order to account for these differences, scientists have to learn more about Titan鈥檚 surface topography and geology.
In addition, Saturn鈥檚 massive gravity affects Titan鈥檚 atmosphere, and this tidal effect could lead to longitudinal variations.
Journal reference: Science (vol 311, p 201)
