In some ways, Saturn's moon Titan is very Earth-like, with its flowing rivers, lakes and oceans. But there's a key difference: instead of plain old water, those seas are composed of liquid methane and ethane. Now, scientists at NASA and Washington State University have recreated that alien ocean in the lab to test out designs for submarines that may one day dive into those Titanic depths.

As the only place besides Earth that's confirmed to have liquid at its surface, Titan is one of the most fascinating worlds in the Solar System. Networks of canyons flooded with liquid hydrocarbons crisscross the moon, feeding into fizzy seas that may reach depths of between 160 m (525 ft) and 300 m (985 ft). Its bizarre, active hydrological cycle means that it could even be home to non-water-based life, so naturally it's a place of interest for scientists.

Most of what we know about Titan comes from Cassini, which was until recently in orbit around Saturn. But there's only so much we can learn from above, so NASA is currently investigating what it will take to get some eyes in the ocean.

It's relatively simple to simulate the rocky Martian surface to test rovers, but nothing remotely similar to Titan's oceans occurs naturally here on Earth. These "waters" are a complex mix of methane and ethane, and can get as cold as -300° F (-184° C). So NASA scientists turned to Washington State University's cryogenic lab to help design and build a special test chamber.

This system housed a tank full of an extremely cold mix of methane and ethane pressurized to 60 lb per sq in, simulating the otherworldly ocean. To see what was happening inside that unwelcoming environment, the researchers used a video camera and a borescope, and managed to observe ethane-methane rain and snow.

To test how a submarine might fare under those conditions, the team placed a small cylindrical cartridge heater in the tank. The electronics on any future sub would produce heat, which would in turn create nitrogen bubbles around the device. The researchers wanted to learn more about these bubbles, since too many of them could cloud the view of the sub or knock it off balance.

Among their results, the researchers found that nitrogen in the mix helps lower the liquid's freezing point, down to -324° F (-198° C), meaning sub-surface explorers won't need to keep an eye out for icebergs. Altogether, the study helped scientists better understand the mechanisms of Titan's seas, which will inform the design of the eventual Titan sub.

The research was published in the journal Fluid Phase Equilibria.

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