Tropical Storms on Titan
New Cloud Formations Spotted on Solar System's Second Largest Moon
Aug 17, 2009
Saturn's largest moon Titan showed an outburst of stormy activity for a brief period in April 2008. This activity changed the way astronomers view the hazy satellite.
New Storms Discovered on Titan
Using the Gemini North Telescope, astronomers have discovered significant cloud formations near Titan's tropics. The outburst of atmospheric activity occurred over the course of a few weeks in April 2008. It was the first time in eight years of monitoring that storms were found in the tropical regions of Saturn's largest satellite.
Clouds on Titan are not rare in general because Titan has the thickest atmosphere of any moon in the solar system. Mid-latitude and polar clouds are common. But the clouds witnessed in the tropical regions in 2008 were not expected because it contradicts with the extremely dry and desert-like conditions found near the equator.
However, scientists already had evidence that something more was happening on Titan. In January 2005, NASA's Cassini spacecraft deployed a probe named Huygens that descended through the atmosphere and took images of the equatorial surface. It discovered small-scale channels and stream beds. Now scientists have a better understanding of how they may have formed.
"These observations show that the channels and streambeds in Titan's tropical desert can be explained by infrequent but strong downpours, much like many of the landforms here in the Southwestern United States," says Henry Roe from Lowell Observatory in Arizona. "Of course these rain showers are not liquid water like here on Earth, but are instead made of liquid methane."
The temperature on Titan is a frigid -178 degrees Celsius, which means that methane is in liquid form on the satellite. This liquid methane appears to be the dominant force behind the moon's weather and surface erosion.
The Tropical Storm's Long-Ranging Effects
The storm that occurred in the tropics of Titan had larger effects on the whole satellite. A convective pulse at mid-latitude generated a wave in Titan's atmosphere. The wave triggered cloud formations in both the equatorial and south polar regions. Cloud development at the south pole during this time was considered improbable due to the Sun's seasonal angle relative to Titan.
The initial cloud system appeared at 30 degrees south latitude but spread over a matter of days to the tropics and south pole. The connection between cloud formations in different areas of the globe is created by a process called atmospheric teleconnections.
"Titan's year is 30 Earth years long and so far we've only been observing Titan with this type of precision and frequency for less than one Titanian season," explains Roe. "Imagine trying to understand Earth's weather having only seen what happens in January, February, and part of March. We have our work cut out for us to continue watching the weather on Titan for many more years."
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