Peculiar crystals could be abundant on Saturn’s largest moon, Titan, potentially creating environments where microbes could live.
at NASA’s Jet Propulsion Laboratory in Pasadena, California, and her colleagues simulated Titan’s methane rain and ethane flooding, and found that a salt-like compound formed quickly and stuck around, even after being repeatedly washed over.
This suggests that the chemical slurry on the surface could create a “co-crystal”. But rather than salt composed of sodium and chloride, these are formed by ammonia and acetylene.
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Hydrocarbon sea and air
“The definition of a co-crystal is not – excuse the pun – crystal clear,” says of Cornell University in New York. “It’s used mostly to denote solid compounds of two or more molecules or ions where the bonding is a bit loose, so the components retain their identities.”
Titan is like a parallel Earth: its thick clouds hide a surface covered in large bodies of liquid and muddy terrain, and it has regular precipitation. But instead of water, Titan’s surface is carved out by liquid ethane, methane and other hydrocarbons streaming and pooling just as water does on our planet.
The existence of co-crystals on Titan has been suggested before, such as a benzene-ethane compound that forms readily in conditions like those of its hydrocarbon seas. Ammonia is known to exist in Titan’s atmosphere and is probably also found in a liquid water ocean deep under the moon’s icy surface.
On the move
This new study suggests that ammonia moves around enough to encounter acetylene through cryovolcanism, precipitation or deposition on bedrock on the sea floor, where it would be in the most direct contact with acetylene.
In the lab, the co-crystals formed within minutes in the simulated environment, meaning they could be common on Titan’s surface. The crystals are hardy, so they can pile up and create many chemical environments. On Earth, we know that having such variety is key to life, so this odd chemistry could give rise to weird life forms.
“While we have little if any info on this type of chemistry, the introduction of ammonia is bound to make it more interesting for prebiotic – or exotic biotic – chemistry,” says Lunine.
It may be some time before we know if the co-crystal is as abundant as these tests suggest. The next opportunity may be Dragonfly, a mission proposed to launch in 2025 that would use a drone quadcopter to hop around Titan’s surface, searching for prebiotic chemistry.
ACS Earth and Space Chemistry
Read more: Summer on Titan may make its lakes ripple with waves
This article appeared in print under the headline “Weird crystals could coat Titan”
