The recent announcement that there might be lakes just under the comparatively thin circular, bumpy features on the surface of the Jovian moon Europa offers tantalizing evidence that the icy outer bodies of the solar are much more dynamic and interesting than thought.
Equally as amazing are the water geysers on the Saturnian moon Enceladus that were discovered by NASA’s Cassini orbiter. They must be fueled by a huge water reservoir under the icy crust.
And, add to this list Titan and Ganymede that also might have subsurface oceans.
Given these discoveries, it’s not too far fetched to think that the icy dwarf planet Pluto could have subsurface oceans too — making it much more than simply the “ice ball” that is quickly shrugged off by the “Pluto is not a planet” detractors.
Billions of years ago Pluto must have been warmer. This would have resulted from a a collision between Pluto and another Kuiper belt object that gave birth to large companion moon Charon and the three additional smaller satellites.
After the impact, Pluto and Charon would have been extremely close together, and spinning rapidly. The strong gravitational tidal pull between the two should have produced enough heat to melt the interior turning Pluto into a giant Slush Puppie. Pluto could have been like Europa for hundreds of millions of years before completely re-freezing over.
Or did it?
Pluto may have a thin shell of nitrogen covering a shell of water mixed with antifreeze-like ammonia. Some models predict a planet-wide ocean with an average depth of 100 miles beneath a 100-mile thick crust. Pluto’s not exactly the best place for ice fishing.
If the ocean is deep enough to contact a rocky core, it would allow for the mixing minerals and salts into the water. Would this nurture the development of some sort of exotic silicon-based “cyrolife” that uses dinitrogen in place of water?
However, the question is most likely a moot point because Pluto offers the lowest chances of identifying life elsewhere in the solar system. A sample return mission would be exorbitantly expensive and extraordinarily difficult compared to looking for extraterrestrial life much closer to Earth.
The planet is so hard to get to, that we will have only a few weeks of close-up views of the Pluto system when NASA’s New Horizons craft flies through it in mid-July 2015.
Could the presence of a past or present subsurface ocean be deduced from the craft’s brief encounter? Well maybe, but only because we have years worth of data of the icy moons in the Saturnian system, and Jupiter’s Galilean satellites as well.
Familiar features may pop up even in long-range pre-encounter views of Pluto. For example, New Horizons will be able to precisely measure Pluto’s diameter. If the planet were slightly oblate it would be evidence for a solidified frozen “bulge,” left over from when Pluto spun more rapidly. If Pluto still has a liquid mantle, material would still flow, reducing the size of the bulge.
If New Horizons imaging reveals a world covered with a crazyquilt “chaotic terrain” of the Europa-type surface fractures, then it would be evidence that an ocean existed at some point. Pluto might also be covered with dead cryovolcanoes that were produced when liquid from the ocean forced its way to the surface. However, the discovery of still-active geysers on the planet would be an eye-popper, and unequivocal evidence for a subterranean ocean.
Regardless, I have no doubt that New Horizons will uncover an extraordinarily complex Plutonian landscape. To date, the best of the Hubble Space Telescope pictures of Pluto show a remarkably variegated surface with of bright and dark regions, some of it molasses colored from photochemical effects from the sun.
Ten weeks out from closest approach, the New Horizons probe’s photographic resolution will exceed Hubble’s. The entire planet will be photo-mapped. At closest approach, features as small as twice the length of a football field will be discernible on Pluto.
Unfortunately, half of the planet will be in darkness during the brief close encounter. Scientists will be left to speculate for decades what secrets the unseen hemisphere might hold.
My prediction is that the images from the near encounter will leave astrogeologists with many more questions than answers about Pluto’s history, internal structure, and dynamics. And, that’s not to mention the chances of a subterranean ocean that is perhaps as illusory as the mythological river Styx in the Underworld.
Image credits: ESA, NASA