Pluto: The Story so Far

On July 14, the New Horizons space probe flew past the dwarf planet Pluto, more than 50 years after Mariner 2 successfully completed a Venus flyby, the first time a space probe visited another world. It's been a long time coming for Pluto. Voyager 1 was nearly sent to Pluto after its Saturn visit, but instead it performed a close flyby of Titan. Honestly, considering how little Voyager was able to learn about Titan given the presence of its thick, inscrutable atmosphere, Titan may not have been the best choice for Voyager. But finally, Pluto has gotten its first visit, and as is tradition with cutting edge science such as this, Pluto gave us quite a few surprises.

One of the most unusual features is actually a lack of a particular feature, namely craters. There just aren't any there. Charon, Pluto's most significant moon, has a few craters, but not nearly as many as one would expect. These are two cold, small bits of ice and rock 3 billion miles from the sun. There's no gas giant to exert any sort of tidal flexing as is the case with some moons orbiting Jupiter and Saturn. Based on what we know, Pluto and Charon should both be dead worlds. But they're not. Pluto's surface seems to be less than 100 million years old, very young when it comes to geology.

Typically, worlds made up primarily of ice don't have big elevation changes. Look at Europa, the surface there is so smooth that a cue ball, expanded to Europa's size, would have greater elevation changes. So, it would make sense then for Pluto and Charon to be pretty much flat, right? Well, apparently not, because both have some pretty impressive topography. Charon has a canyon that could be up to 6 miles deep, just one of many canyons in a vast network that span for hundreds of miles. Charon also has a plain near the northern pole that scientists have been informally calling Mordor. I hope that name sticks.

Not to be completely outshone, Pluto has its fair share of interesting geography. Of course, there's the heart, which I believe has officially been termed Tombaugh Regio after Pluto's discoverer. Then there's the mountains. Now at the cold temperatures we're familiar with, water ice is pretty soft and not really capable of getting very high. Pluto is an entirely different sort of cold, cold enough for

strange and unusual ices like methane ice and nitrogen ice. At those temperatures, water ice because solid enough to build mountains. These are real mountains too, with the highest peaks soaring up over 10,000 feet. Sure, we've got higher here, but for a little chunk of basically ice, Pluto didn't do too badly for itself.

It's going to take a long time for New Horizons to send back all the data it collected during its brief visit, more than a year. Right now, we still barely know anything. I'm sure I'll be writing more posts about Pluto in the future as the data slowly trickles in. To wrap things up today, I just want to say that Pluto is not a planet, it just isn't big enough. That said, that doesn't make this achievement any less spectacular.