New Horizons has caught our attention, or at least it should have. Pluto is about 5,874,000,000 km from the sun, or 39.26 times as far from the sun as Earth is. The reason I say “about” is that the orbit is eccentric, and sometimes is closer to the sun than Neptune is, but it is an orbital resonance with Neptune, so it will never collide with it (unless something else disturbs the resonance). The space craft flew by Pluto at about 50,000 km, so think of the triumph of getting that accuracy. The cameras can see objects down to about a kilometer in size.
Pluto is actually smaller than our moon, and has only 18% of our moon’s mass, but because it is about 1/3 ice, it has more water than Earth. When Pluto gets closer to the sun, it has a weak atmosphere of nitrogen, and probably some carbon monoxide and maybe methane and argon. As it gets further from the sun, these gases snow out. The surface temperature varies, but is in the order of minus 230 degrees Centigrade. That much we knew.
Pluto has an interesting history, in that it was predicted by Percival Lowell in 1915 based on deviations found in the orbits of Neptune and Uranus. Neptune itself was discovered because the orbit of Uranus did not follow Newton’s laws exactly, but it would if there were another giant planet pulling on it. Accordingly, astronomers could predict where Neptune would be, they looked, and there it was. A triumph for physics. However, Neptune’s orbit was still not right, so Lowell predicted a further planet, calculated where it should be, and Clyde Tombaugh found it in 1930. Another triumph! Nevertheless, this shows an important fact, namely just because you can predict something that turns up, that does not mean the basis of the prediction was correct, as Pluto is far too small to account for what Lowell calculated. The discovery was a happy accident.
So, what have we discovered about Pluto? In my opinion, so far, not a lot, but that is mainly because most of the data will not come in for months. We have corrected Pluto’s size, but that is not a huge achievement. However, the images have given us a lot to think about. The one thing that has surprised us is that Pluto is geologically active, and far more so than anyone might have expected. I have seen statements that it must have been essentially resurfaced about a hundred million years ago. I am not too sure about that, as it is based on crater count, and I doubt anyone has any good data on collisions that far out. Furthermore, if the bodies out there are largely icy, and Pluto’s surface is mainly ice, then because collision velocities will be a lot slower out there, it is possible that collisions will not excavate a crater, but rather the energy will melt the ice, it will flow, then re-freeze, thus not forming a crater. Nevertheless, the mountains, canyons, and the flat areas are indicative that there has been significant internal heat. That could come from a number of sources, such as radioactive decay, collisions, one of which may have formed the moon system, and possibly even a little chemistry.
The heat may not have to be intense if it is uneven, because it would volatalise gases such as nitrogen, and that would create a lot of internal stress. Another form of internal stress may come from freezing water. If the outer layers are largely free of rock, that having sunk to the core, then because water expands a little on freezing, that “little” will be magnified into quite a change of length over the circumference even of a dwarf planet, and with nowhere to go, there could be considerable additional warpage. That is unlikely to account for all the mountains, etc, but it may add to the cause and magnify it.
What do we think we know about Pluto? Try this link: http://www.forbes.com/sites/fayeflam/2015/07/21/the-weirdest-reason-pluto-didnt-become-a-real-planet/
Here, they argue Pluto grew in the region of Jupiter/Saturn, and with Uranus and Neptune, were thrown out into the outer solar system, where there is not enough material to grow. I don’t believe that, because I don’t believe the standard theory of planetary formation, which starts off by assuming that the dust accretes into planetesimals by some unknown mechanism, and these collide to form larger objects, and finally, planets. The reason the outer giants had to start in the Jupiter/Saturn region is that collisional probabilities are too low to get giants much further out under this mechanism. In my “Planetary Formation and Biogenesis”, I argue the first step is actually based on physical chemistry, essentially the same mechanism as forming a snowball, and the planets form at temperatiures where the various ices assist. Ion this theory, Pluto, and the other Kuiper Belt objects formed by the same mechanism that Neptune formed, but because the temperatures were starting to get too low, accretion was slow, but because they were far enough away, they did not get “collected” by Neptune.
So, will we find out more? Basically, we now have to wait for more data, but in the meantime we should congratulate NASA on a truly great achievement. They still have “the right stuff”.