Geological Activity on Pluto and Charon

Pluto Close-Up - 14 July 2015Before New Horizon’s flyby of Pluto, I noted that the dwarf planet might have geological activity. But I was unprepared for the reality. The scientists studying the little bugger have not found a single impact crater. You can see this in the image on the right. According to their calculations, this means that there must have been geological activity on Pluto within the last hundred million years — a very small amount of time in the 4.5 billion year history of the solar system. But it could be that there is geological activity going on right now.

John Spencer, a New Horizons mission scientist, explained that this is an important finding. The only place where we’ve found geologically active on cold worlds have been in moons that experience tidal heating. This is where the planet’s gravitational field constantly deforms different parts of the moon, causing the interior to heat. This is what happens on Jupiter’s closest large moon, Io. And as a result, Io is the most volcanically active place in the solar system. But there is no large object near Pluto. So where is the heat coming from that at least very recently was being expelled? We don’t know, but then we didn’t even know it was possible a couple of days ago. Spencer cheekily said at a press conference, “You do not need tidal heating to power geological activity on icy worlds. That’s a really important discovery we just made this morning.”

Charon - 14 July 2015Another interesting aspect of the whole thing is that Pluto has more nitrogen in its atmosphere than it ought to, because the gas should reach escape velocity. Before this recent flyby, New Horizon’s chief scientist Alan Stern and a colleague predicted that if they saw steep water-ice mountains with a thin volatile gas veneer, it would indicate that there is some kind of geological process that is dredging up nitrogen from the interior. Well, as you can see in the image above, Pluto has very high (two mile), very steep ice mountains. And they have a “thin frosting of nitrogen and other volatiles.” They haven’t found any “geysers” or “cryovolcanoes.” But they only just started looking.

Also interesting is that Pluto’s biggest moon, Charon, shows signs of recent geological activity. It does have very clear craters. But it is nothing like our Moon. And the whole thing is amazing. Of course, the scientists have lots of theories as to why this might be. Stern mentioned the possibility of the liquid layer under both objects that are slowly solidifying and thus giving off heat. Personally, I think that sounds far fetched for Charon, but maybe works for Pluto.

What is so cool about this is that for hundreds of years, humans have been trying to figure out the cosmos in a very systematic and rigorous way. Yet each time we get another close look at some part of the cosmos, we have major rethinking to do. As Stern noted, this new information will “send a lot of geophysicists back to the drawing boards.” And that’s wonderful! That’s the way science works: you have a theory and you stick with it until reality shows that it is wrong. But it highlights the fact that we have so much to learn, so many more spacecraft to launch, so many more theories to explode!


I found this same thing just in terms of trying to explain how our very own planet’s magnetic field works. And I’m still researching that, trying to figure out what the hell is actually going on. It is possible to see Hamlet talking about science and not metaphysics, when he said, “There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy.”

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