What does not have a subsurface ocean these days? Even Pluto is a candidate, as NewScientist (2 July 2016) suggests from an article in Geophysical Research Letters by Noah Hammond, Amy Bar, and Edgar Parmentier:
If Pluto still has an ocean, then global volume expansion would still be occurring, suggesting extensional tectonic activity could be ongoing. This is consistent with the observations of Moore et al. [2016] who suggest that the relative youth of tectonic features could be consistent with the partial freezing of an ocean. Additionally, tensional stresses at the surface and ocean pressurization, due to the ice shell thickening, could make cryovolcanic resurfacing more likely [Robuchon and Nimmo, 2011].
Or, as NewScientist puts it:
If it had frozen solid, the pressure from the outer ice would have squished the ocean into a denser form called ice-II, reducing its volume. Pluto would have contracted, covering it in wrinkles.
But New Horizons saw deep cracks instead, suggesting Pluto is slowly growing through the formation of normal ice, which has a larger volume than liquid water.
NASA suggests Pluto’s moon Charon may have had an ocean in the past.
If anything swims in that ocean, it’ll need anti-freeze for blood – like certain fish. Wondering about ice-II?
Ice II is a rhombohedral crystalline form of ice with a highly ordered structure. It is formed from ice Ih by compressing it at temperature of 198 K at 300 MPa or by decompressing ice V. When heated it undergoes transformation to ice III.[1] Ordinary water ice is known as ice Ih, (in the Bridgman nomenclature). Different types of ice, from ice II to ice XVI, have been created in the laboratory at different temperatures and pressures. It is thought that the cores of icy moons like Jupiter’s Ganymede may be made of ice II.
Credit: NASA/JHUAPL/SwRI via slate.com.
