Titan experiences intense rainstorms

Fan-shaped regions of alluvial deposits correspond exactly with areas of highest rainfall.
By Laurel Kornfeld | Oct 16, 2017
Titan, Saturn's largest moon, experiences intense rainstorms that produce flooding in terrains that are usually dry, according to a new study published in the journal Nature Geoscience.

A team of geologists and planetary scientists at UCLA studied radar images of fan-shaped sediment deposits on Titan captured by instruments on board NASA's Cassini Saturn orbiter, which studied the planet and its moons from late 2004 to its plunge into the gas giant's atmosphere on September 15, 2017.

Beginning with the discovery of sand dunes in Titan's lower latitudes soon after the spacecraft began orbiting Saturn, scientists have focused heavily on the moon's surface.

Seas and lakes of methane and ethane were found in its higher latitudes. The fan-shaped regions are located at latitudes ranging from 50 to 80, at the centers of both the northern and southern hemispheres.

Surface variations indicate different regions of a planet experience varying levels of precipitation, as erosion of land and filling of lakes occur through rainfall runoff.

In contrast, dunes form in dry areas that do not experience much rainfall.

Extreme rainstorms, which scientists now believe occur approximately once every Saturn year--29 and-a-half Earth years--may transport sediment around Titan's surface and cause erosion in some regions.

Cassini observed just three seasons on Titan, so the researchers had to rely on computer simulations to model the large moon's hydrologic cycle, which involves methane and ethane rather than water.

The models confirmed observations by the spacecraft that rainfall occurs mostly near Titan's poles, close to its lakes and seas. They also indicated the most intense rainstorms occur near 60 degrees latitude, which is where most of the fan-shaped deposits, also known as alluvial fans, are concentrated.

UCLA graduate student Sean Faulk, lead author of the study, compared the impact of Titan's methane rainstorms to that of water rainstorms on Earth's surface.

"The most intense storms in our climate model dump at least a foot of rain a day, which comes close to what we saw in Houston from Hurricane Harvey this summer," said Jonathan Mitchell of UCLA, a senior author of the study and also principal investigator of UCLA's Titan climate research modeling group.

Titan's storms may be the product of temperature differences between cool, wet conditions in its higher latitudes and warm, dry conditions in its lower ones, a phenomenon very much akin to temperature differences that produce severe storms on Earth.

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