An artist’s impression of a lake at the north pole of Saturn’s moon Titan NASA/JPL-Caltech
If you visited Saturn鈥檚 biggest moon a few hundred million years ago, you may have witnessed explosions that left behind huge craters. Those craters would have turned into some of Titan鈥檚 strange lakes of liquid methane, the only lakes we鈥檝e ever seen on a world other than Earth.
The simplest way lake basins form is by liquid dissolving the ground into a divot, so that is how we have long assumed that Titan鈥檚 lakes were formed. But NASA’s Cassini spacecraft found some lakes with rims around them that could not have been formed that way.
These lakes also tend to be irregularly shaped rather than round, which led Jonathan Lunine at Cornell University in New York and his colleagues to discount the possibility that they were formed from impacts. Instead, the team say these craters may be remnants of explosions just beneath Titan鈥檚 surface hundreds of millions of years ago.
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鈥淭hey鈥檙e not very circular which implies that there are multiple popping points, which we also see in explosion craters on Earth,鈥 says Lunine. On Earth, this kind of popping happens when hot magma seeps up from underground, hits cool water and explodes.
On Titan, the most likely way to make such an explosion is with underground liquids that get warmed up, perhaps by an asteroid strike or a change in the convection of the icy moon鈥檚 core, and turn into pressurised vapour. 鈥淭here isn鈥檛 enough oomph in the methane to really do this,鈥 says Lunine. Even though methane is the main liquid on Titan now, it would not explode to create these craters.
But nitrogen would, and there is reason to suspect that earlier in Titan鈥檚 history it may have had a colder, more nitrogen-rich atmosphere and liquid nitrogen on its surface. The researchers calculated that exploding nitrogen could have led to the weird lake beds that we see today.
鈥淢ultiple processes form lakes on the Earth, so why not on Titan?鈥 says Lunine. 鈥淭itan is very much like the Earth in having multiple geological processes that produce features rather than being driven by just one or two processes like some moons in our solar system.鈥 These explosions are yet another way that Titan is more similar to Earth than to any other moon we know of.
Nature Geoscience
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