For the first time, scientists are able to see evidence of rainfall at the equator of Titan, Saturn's largest moon. Except it isn't water, it's liquid methane. It is now spring on Titan, and and infrared camera on board NASA's Cassini spacecraft was able to detect signs of "substantial" precipitation on vast fields of dunes near the equator. Rain on the dunes would sound kind of pleasant if it wasn't freezing and flammable.
In the image above, you can see a huge white arrow shape, which is the storm blowing across the equatorial region. The precipitation cycle on Titan involves the hydrocarbons methane and ethane, which pool in thousands of lakes around the North and South poles.
Titan's atmosphere is very hazy and smoggy, and it is usually hard to see anything on the surface, but astronomers believe that the equator of the moon is circled with huge sand dunes up to 9 feet high, half a mile wide, and 50 miles long. The dunes are surrounded by dry river channels, possibly remnants of a wetter climate.
With the data from the Cassini probe, scientists compared images of Titan's dunes between August 2009 and January 2011. Looking at sudden brightness decreases on the moon's surface after clouds had passed over the region, the scientists were convinced that the ground was darker because it was wet. Dr. Elizabeth Turtle, a planetary geologist at Johns Hopkins University said, "It may be a case of surface wetting. It wouldn't take much. A millimeter of rain over this area would have done it."
According to Dr. Turtle, these findings are evidence that Titan, which is the only moon in the solar system with a dense atmosphere and stable liquids at its surface, has weather patterns that similar to Earth's. "We are seeing seasonal changes in the weather on Titan and that gives us insights into its climate," she said.
But researchers don't know yet how often Titan gets rain. Since the moon is at the outer reaches of the solar system, and orbits very slowly, spring only comes every 30 years.
Titan is interesting as a study to Astronomers and biologists, since the methane clouds and super-chilled hydrocarbon lakes (which can be as big as our Great Lakes) represent a "a great example of pre-biotic chemistry," similar to Earth's early atmosphere, according to Dr. Turtle. But temperatures on Titan are too extreme for terrestrial life to emerge. It's usually a balmy 290 degrees Farenheit below zero on the moon.