The New Horizons mission to Pluto has been a huge success and has so far raised several questions. Arguably the biggest and most surprising question is why is the surface so young. The surface of Pluto seems surprisingly devoid of craters. A crater-less surface suggests there is some process removing them. Not only is there an absence of craters, New Horizons has also spotted ice moutons as high as 11,000 feet.
It is a well known fact that smaller objects cool faster than larger ones of the same shape because of their larger surface area. This principle also holds true for planets (and dwarf planets in Pluto’s case). A warm internal temperature is responsible for the geological activity we see on Earth that is responsible for removing most of its craters as well as creating mountains and canyons. But Pluto is tiny.
Look at the moon for example. It is completely cratered because it is completely geologically inactive. There is no process to fill in craters. But Pluto is smaller than our own moon. Shouldn’t it have long cooled long ago, considering it is 4.5 billion years old along with the rest of the solar system?
Scientists are trying to explain how Pluto is still geologically active.
There are some small bodies similar in size to Pluto that are geologically active in our solar system. These include Europa and Enceladus. They contain subsurface oceans caused by the tidal pull of Jupiter and Saturn respectively. The water in these oceans occasionally wells up from cracks in the surface and fills in craters leaving a young surface. It is possible that Pluto’s moon Charon can tug on Pluto and cause a subsurface ocean but scientists on the New Horizons team say this is very unlikely.
“That can’t happen on Pluto, because there is no giant body that can deform it on a regular basis. This is telling us that you do not need tidal heating to power geologic activity on icy moons. That’s a really important discovery that we just made this morning.” John Spencer, a researcher from the Southwest Research Institute said.
However, the subsurface ocean on Pluto could still be present. Heat from the radioactive decay of potassium could have kept parts of Pluto in liquid form allowing its surface to stay young.
If Pluto is still radioactively active, this suggests planets (or, again, dwarf planets) can maintain radioactive activity much longer than previously thought.
The surface features of Pluto’s young surface will, for now, remain a mystery. But I’m confident the New Horizons team will come up with an answer.