On the left, a black and white image of Pluto released this week by NASA New Horizons shortly before closest approach. On the right, a hypothetical image of Pluto produced in 1979 by artist Don Dixon. Used with special permission. Click image for original art at Don's website
Thanks to New Horizons we now know what Pluto really looks like. It looks a lot like that image up above, except there's one fascinating fact about that pic: it was done in
1979. The artist is Don Dixon and he was able to nail Pluto's appearance using a few
educated guesses:
I'd like to claim prophetic powers, but the painting was guided by the reasonable assumption that Pluto likely has a periodically active atmosphere that distributes powdery exotic frosts into lowland areas. The reddish color of the higher features is caused by tholins – hydrocarbons common in the outer solar system. The partial circular arcs would be caused by flooding of craters by slushy exotic ices. Pluto is apparently more orange than I painted it, however; I assumed the exotic ices would push colors more into the whites and grays.
But now we have real images of Pluto and its many moons, including the oversize Charon. If the Earth's moon was as large and as close to us proportionally as Charon is to Pluto, it would raise tides tens of meters high in our planet's crust and cause thousand-meter tsunamis to sweep over the world every day.
There's a lot of weirdness going on with Pluto and we can infer a lot of weirdness in Kuiper Belt Objects in general. Dive below the fold to see how weird the place really is, thanks in large part to its status as a binary KBO.
Charon, Pluto's very large "moon" for lack of a better term
A lot of the weirdness of Pluto can be explained by two big factors. It's a Kuiper Belt Object and it has a huge over-sized moon. In fact, just as it's not settled whether Pluto is a planet, or what a planet really means if it is, Charon may not be a moon, or if it is, it could redefine what a moon can be. Charon is so big and so close that it doesn't orbit Pluto so much as it dances with it around a common center of gravity.
A side view of the Pluto-Charon system. Pluto and Charon are tidally locked to each other. Charon is massive enough that the barycenter of Pluto's system lies outside of Pluto, thus Pluto and Charon are sometimes considered to be a binary system.
So if you're on one the other, three tiny known moons of Pluto, that bouncing center of gravity causes some peculiar movements that were heretofore unfamiliar to most fans of of planetary astronomy.
That's a reconstruction of how Nix would behave as observed from a stationary point relative to the sun. It behaves this way because it doesn't orbit Pluto, it orbits a dynamic, shifting center of gravity between Pluto and Charon. If the Earth moved like that, there would be "days" where the sun rose in the east and set in the east, the North Pole would periodically become the South Pole ... yeah, it's that weird.
And all this weirdness takes a toll on Pluto's surface—at least that's the strong suspicion of planetary geologists pouring over images like the one above. Between objects occasionally striking Pluto and liquifying large sections of its icy crust, and Charon out there swinging, it acts like a square dance partner causing shifts in the very crust and mantle of the strange little world. In fact, it wouldn't be surprising if Pluto suffers occasional cryo-volcanoes and Pluto-quakes of Biblical proportions.
Beyond that we'll probably have to wait. New Horizons is speeding away from the whirligig system at about 9 miles a second, and its data transmission capacity at that enormous distance is limited. It is predicted it will take over a year for all the data from all the instruments aboard to be sent back. But we should have some great images well before then!