Astronomers believe that Pluto and its moon were the result of two massive objects slamming into each other. The resulting gravitational dynamic may have warmed the interior of Pluto, creating an ocean comprised of liquid water. Remarkably, this underground sea could still be there.
The idea that Pluto has an ocean underneath its icy surface is not new. Back in 2011, astronomers speculated that, despite its frigid surface temperature, the distant minor-planet could host liquid oceans if two conditions were met. First, it has to have a core rich in potassium to produce enough radioactive decay. And second, the flow of ice on the surface needs to be sufficiently slow-moving (otherwise too much heat would be wasted).
Seems a bit speculative, and it is. But a new scenario, as proposed by Amy Barr and Geoffrey Collins, suggests a different kind of process.
Billions of years ago, Pluto's moon Charon was created after a giant object smashed into its icy mantle. The subsequent release of heat may have melted the interior of Pluto, creating an ocean that would have survived for a remarkably long period. And in fact, it could still be there.
According to the researchers, Pluto may still be warm enough to harbor an ocean beneath more than 62 miles (100 km) of ice. This is possible because liquid water, once mixed with other materials, like ammonia and low-eutectic salts, takes on properties similar to antifreeze.
Excitingly, we may be able to find even more evidence to support this theory once the New Horizons spacecraft gets there in July 2015. Should it detect signs of ancient tectonic activity — which would appear as scars and fault lines on the icy surface — it would further the notion that Pluto had or may still have an internal ocean.
According to computer simulations, these hypothetical tectonic faults — the product of a short-lived tectonic system — would have formed soon after the initial collision when both celestial bodies were still warm. The resulting tidal heating could have fostered a liquid ocean, which would have left its mark on the surface. As the authors write:
Orbit and spin evolution of the Pluto/Charon system is driven by the raising and lowering of tidal bulges on each body. The tidal bulges exert torques which change the semi-major axes of the orbits and the spin rates. The mechanical energy associated with the periodic raiding and lowering of the bulges is dissipated as heat in the bodies' interiors. Changes in bulge height and energy dissipation are thought to drive endogenic resurfacing and tectonic activity on many of the icy satellites of the outer solar system.
But for New Horizons to make the observation of tectonic faults, we'll have to hope that Pluto hasn't produced enough atmospheric weather to erode the surface (which is a possibility).
All this said, because we don't know Charon's precise impact on Pluto's internal structures (mostly because we don't know its exact historical orbital location), two other plausible scenarios exist.
First, Pluto may be a differentiated object with no ocean (with ice above rock). In this case, Pluto's icy shell is stubbornly fixed to its rocky core, which would prevent significant tidal deformations and slow the rate at which momentum is exchanged between the two bodies. The other possibility is that it's just an undifferentiated rock and ice mixture.
Of the three possibilities, the going evidence favors the liquid ocean model.
Read the entire study at Icarus: "Tectonic Activity on Pluto After the Charon-Forming Impact. Read it for free at arXiv."