In July 2015, we get our first close look at the dwarf planet Pluto and its moon, Charon, a fact that has scientists hypothesizing more than ever about what we might see there.
One of the latest ideas put forward is that perhaps the collision that likely formed Pluto and Charon heated the interior of Pluto enough to give it an internal liquid water ocean, which also gave the small world a short-lived plate tectonics system, like that of Earth.
“We predict that when New Horizons gets there it will see evidence of ancient tectonism,” said Brown University's Amy Barr, coauthor of a new paper with Geoffrey Collins in the latest issue of the journal Icarus. By "ancient," Barr means sometime way back during the first billion years of the solar system's history.
Barr and Collins modeled the Pluto-Charon system based on the idea that the initial collision of the two bodies would have generated enough heat to melt the interior of Pluto creating ocean that would have survived for quite a while under an icy crust.
“Once you create an ocean on an icy body, it's hard to get rid of it,” said Barr. That's because as the ocean freezes, the remaining liquid portion gets enriched with salts and ammonia -- which serve as antifreeze.
Next comes the part where that ocean could have created icy tectonic plates on Pluto's surface.
“One thing that we know is the angular momentum will be conserved as the system evolved,” said Barr.
With that fact, they simulated a bunch of scenarios based on where Charon's orbit was right after the collision -- since nobody actually knows where Charon started. Then in each scenario they saw Charon's orbit gradually migrate outward -- just like the moon's orbit did around Earth.
When Pluto and Charon were closer and still hot from their collision, they pulled more forcefully on each other and were more egg-shaped as a result. But as Charon moved away, Pluto became more spherical. To change shape, the icy surface would have had to crack and create faults -- telltale signs of tectonics.
“In the scenarios we see, you generate more than enough stress to create all kinds of tectonic features,” Barr said.