The Outermost Ocean in Our Solar System: Neptune’s Triton



A new study suggests the presence of an ocean under the icy shell of Neptune's moon, Triton, which will make it the outermost known ocean in our solar system. At an average temperature of -97° C, this ammonia-rich ocean was sustained over 4.5 billion years by tidal blanketing and radiogenic heating. The ammonia keeps the liquid from freezing unless the temperature drops below about -90 °C. 

The composite NASA  illustration above shows Neptune as seen from Triton. Neptune's south pole is to the left; clearly visible in the planets' southern hemisphere is a Great Dark Spot, a large anti-cyclonic storm system. This three-dimensional view was created using images from the Voyager spacecraft

Saswata Hier-Majumder of the University of Maryland and colleagues have developed a detailed model that considers both radioactive decay of core minerals and the orbital interactions that would have heated the moon. Although heating from radioactive decay is orders of magnitude larger than heating from tidal effects, heat from the core alone could not keep the outer layer from freezing over the 4.5 billion-year life of the solar system, they say.

The team have found that even a small amount of heating from orbital forces makes a significant difference because it is applied to the base of the ice covering the subsurface ocean. "It puts a warm blanket on top of the cooling ocean," says Hier-Majumder. As long as the orbit is so circular that its 350,000-kilometre-radius varies by only a few kilometres, Triton should still have a substantial ocean beneath its surface.

The Daily Galaxy via Icarus, DOI: 10.1016/j.icarus.2012.05.006 and

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