This week, we saw this on Pluto:
This surface has no yet-identified impact craters in it. Instead, there are very tall mountains of unknown geology, some weird puffy deposits near the limb, obscuring underlying geology, a rille I cannot explain, except maybe it’s a fault or an escarpment. Some isolated mountains with what might be calderas in them, and a bunch of smooth terrain. All of that is evidence for active geology on a world which according to (prior) conventional planetological wisdom, just shouldn’t be able to do that.
What does it mean if Pluto has active geology driven by a subsurface mantle/ocean? Why is that so exciting? There are many reasons, but let me explain why it gives me a chill.
Caution: the following is wild speculation, not any kind of solid science!
In bioastronomical terms, it might be a bombshell.
Sometime back, we realized that, underneath the ice, Europa may have an ocean very much like Earth’s oceans. It may even have a geothermal power source in terms of subsurface vents that might have replaced the energy from sunlight as a means of bringing about the origin and evolution of life.
There may be fishes in that sea.
Since then, we’ve looked at other icier worlds, like Enceladus, and… WOW: we see similar stuff! Enceladus probably has a sub-surface ocean, too, even though it is much smaller and lighter than Europa. Whether it has the other chemistry needed to support life is unknown, but it may — such bodies generally are expected to have silicate cores and impurities throughout the water ice. They also have even larger inventories of basic organic compounds than does the Earth (as a fraction, I mean — they’re smaller worlds).
Several of the icy moons in the outer solar system probably have a water mantle or “ocean” like this at some depth — although some will be a lot deeper.
It is possible not only that these places are abodes for life, but that they may be the primary abode of life forms in the universe, and that “Earth-like” planets are more of an exceptional case. (Because icy little worlds like Enceladus are probably a lot more common than “Earths”).
Until recently, we thought we understood where the energy to power these geologically-active icy moons came from — we thought it was tidal forces from the giant planets they orbit.
However… remember (the largest belt asteroid) Ceres, with the bright spots that are probably new surface deposits of either water or salt? Well, Ceres doesn’t have a giant planet warping it with tidal stress either, so some kind of power source is driving that.
And something like Ceres lives inside of icy worlds like Enceladus or Triton, or Pluto. Because they generally have some silicate core deep under the icy mantle and crust. If whatever drives the activity on Ceres is driving activity in the core of Pluto, then it could be melting the ice above it and creating a water ocean/mantle on Pluto, like the ones we theorize are inside of the icy moons of Saturn or inside Triton.
Pluto gets very little sunlight.
If it’s got that kind of power, it’s not coming from the Sun, and that means that if it can happen at Pluto, it can happen at Eris or Sedna or in large objects in the Oort cloud — or even drifting through interstellar space. (And remember also — Eris is much denser than Pluto. It may have a larger and thus more powerful core).
Data from Kepler suggest that there is quite a large population of rogue planets in the galaxy, even of large jovian-sized planets. Presumably little icy planetoids would be even more common.
There is probably a HUGE population of tiny little icy worlds in the universe, in a wide variety of different sizes, densities, and dynamical environments.
So, it’s possible that there are little icy, enclosed life incubators strewn throughout the galaxy. That might raise the possible locations for life to originate by a couple of orders of magnitude!
Of course, we might question whether such life would ever manage to escape its tightly-enclosed, hermetically-sealed universe into the larger universe outside? Would they ever even wonder what is above the solid icy dome of “heaven” through which no night sky can be seen? Who knows? It’s probably not impossible anymore than spaceflight is impossible for us, though it may take them a long time to discover it.
This is big, long line of speculation with lots of ifs. It’s a bit like Sagan’s “Observation: I can’t see a thing. Conclusion: Dinosaurs” regarding Venus. So keep that grain (or bucket) of salt at hand.
It’s not worthy of being called a “theory”. Maybe a “hypothesis” or as I call it “wild speculation”.
Because of that, working scientists are very hesitant to come out and say stuff like this. It’s too wild, and with the low-quality of science journalism, “it might lead us to wildly speculate” is likely to be shortened to “scientists say…” removing all nuance and doubt, which could make us all feel very foolish someday.
But if you’re pondering why scientists get excited about this kind of information — this is one reason why. It could be shattering to our view of how the universe (and life in it) works. And I just wanted to connect those dots for you.
How to answer the question?
Someday, I hope we’ll have solid evidence one way or the other. Lander or subsurface missions to Europa or Enceladus might tell us a lot more. A flyby of Eris or even Sedna might show us an active surface there, too, and that would be even more stunning (we also see some geological activity on Charon, which is even smaller than Sedna!). Perhaps Dawn will be able to tell us what’s going on with Ceres, and give us a good theory for how the power is generated (there are some theories, ranging from latent heat storage mechanisms, to radioisotope heating, to very slow geochemical processes that might generate heat).