Titan: A Moon Shaped By Its Rainstorms

The more we investigate Saturn’s largest moon, Titan, the more it surprises us and the more we understand that it isn’t so different from our own planet, minus the methane lakes perhaps.

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Titan is the only place in the solar system, aside from Earth, with a dense, nitrogen-rich atmosphere which makes it a superb hunting ground for scientists and researchers. Not only does it have a nitrogen-rich atmosphere, but it also has surface liquid and clouds which operate in a similar way to our own water cycle, albeit with methane instead of water.

Whilst NASA’s Cassini mission might have grabbed the headlines for its plume discoveries on Enceladus and ring composition work, Cassini also had a little look at Titan and gave us some interesting data to work with. And, we also shouldn’t forget that we actually sent a lander to Titan, back in 2005 which hitched ride with Cassini, and beamed back some incredible images and data from the mysterious world.

An experienced team of UCLA planetary scientists and geologists looked closely at the data sent back and investigated Titan’s methane rain storms, which despite being fairly uncommon, appear to be extremely violent, much like hurricanes and monsoons on Earth. The team published a study called “Regional Patterns of Extreme Precipitation on Titan Consistent with Observed Alluvial Fan Distribution” in the scientific journal Nature Geoscience.

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Simulations were conducted to test whether these storms had any impact on shaping the moon over millions of years. At first you might dismiss the idea of a rainstorm having any effect on the shape of a planetary body, but we should remember that even rivers and waterfalls affect the malleable planet Earth. The study declares that the methane certainly has shaped the icy world in a similar way that Earth has been shaped by our own precipitation system.

Alluvial fans are formed on Earth when heavy rainfall causes large flows of water to move sediment and rocks along its path and into low lands where new features are formed. Cassini found evidence of similar activity on Titan which was almost certainly formed by the methane clouds and rain.

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The alluvial fans aren’t the only geological formations being investigated in the study, as the researchers also looked at the vast sand dunes that sit lower latitudes and the seas that makeup much of the higher ones. 3 vast oceans of liquid methane, Kraken Mare, Ligeia Mare, and Punga Mare, measure hundreds of miles across and are thought to go fairly deep. There are also many smaller lakes found in shallower areas.

Computer simulations tested how the rainstorms could form these lakes and seas and found some interesting results. It was no surprise that the rainfall mostly occurred around the poles of the moon, where the major lakes and seas are situated. The alluvial fans are situated in the areas where we might expect the liquid to flow after pushing the debris and sediment.

Jonathan Mitchell – a UCLA associate professor of planetary science – indicated, this is not dissimilar to some extreme weather events that were recently experienced here on Earth.

“The most intense methane 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. I would have thought these would be once-a-millennium events, if even that, so this is quite a surprise.”

The team also worked out that the torrential rainstorms occur once every 30 Earth years or so, or once per Titan year, which indicates that it is a seasonal effect and could be caused by changing temperatures and moisture. When they first began the study, they expected this was a lot rarer.

The study indicates to us that Titan has a lot more in common with Earth than we first imagined. Extreme temperatures changes cause the extreme weather conditions that shape the planet.

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