In a sneak peek of a potential future mission to Saturn’s moon Titan, NASA has displayed their vision of a robotic submersible that could discover the moon’s vast lakes of liquid methane and ethane. Exploring Titan is believed to be looking back in time at an embryonic Earth, only a lot colder. Titan is the only moon in the solar system to have a noteworthy atmosphere and this atmosphere is well-known to have its own methane cycle, like Earth’s water cycle. Methane subsists in a liquid state, raining down on a landscape laced with hydrocarbons, forming rivers, valleys and seas.
Several seas have been broadly explored by NASA’s Cassini spacecraft during several flybys, some of which average a few meters deep, while others have depths of over 200 meters (660 feet) — the maximum depth at which Cassini’s radar tool can penetrate.
Envisaged as a probable mission to Titan’s biggest sea, Kracken Mare, the independent submersible would be designed to make a 90 day, 2,000 kilometer (1,250 mile) voyage studying the depths of this vast and very extra-terrestrial marine environment. As it would spend long periods under the methane sea’s surface, it would have to be power-driven by a radioisotope generator; a source that transforms the heat generated by radioactive pellets into electricity, much like missions that are at present studying space, like Cassini and Mars rover Curiosity. Communicating with Earth would not be potential when the vehicle is under the sea, so it would need to make regular ascents to the surface to communicate science data.
But Kracken Mare is not a tranquil lake fit for moderate sailing — it is known to have choppy waves and there is proofs of tides, all contributing to the challenge. Many of the engineering challenges have by this time been encountered when designing terrestrial submarines — robotic and crewed — but as these seas will be enormously cold (projected to be close to the freezing point of methane, 90 Kelvin or -298 degrees Fahrenheit), a special piston-driven propulsion system will need to be developed and a nitrogen will be required as ballast, for example.
This study is just that, a study, but the option of sending a submersible robot to another world would be as extraordinary as it is splendid. Although it’s not clear at this early phase what the mission science would focus on, it would be stimulating to sample the chemicals at different depths of Kracken Mare.
“Measurement of the trace organic components of the sea, which possibly may exhibit prebiotic chemical evolution, will be an important objective, and a benthic sampler (a robotic grabber to sample sediment) would acquire and study sediment from the seabed,” the authors write (PDF). “These measurements, and seafloor morphology via side scan sonar, may shed light on the historical cycles of filling and drying of Titan’s seas. Models propose Titan’s active hydrological cycle may cause the north part of Kraken to be ‘fresher’ (more methane-rich) than the south, and the submarine’s long traverse will study these compositional differences.”
A decade after the European Huygens probe landed on the surface of Titan imaging the moon’s eerily foggy atmosphere, there have been few plans to go back to this tempting world. It would be improbable if, in the next few decades, we could send a mission back to Titan to directly sample what is at the bottom of its seas, studying a region where the molecules for life’s chemistry may be present in large quantity.
So, if researchers are to appropriately study Titan, they must find a way to dive into these seas to disclose their secrets. At this year’s Innovative Advanced Concepts (NIAC) Symposium, a Titan submarine idea was displayed by NASA Glenn’s COMPASS Team and scientists from Applied Research Lab.
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