Pluto’s Glacier and Atmosphere

PlutoIt is a bit weird to go to the Wikipedia Pluto page. Just a month ago, the best image that we had was a fuzzy ball. Now we have a shockingly clear picture of it. It is as though we are, for the first time, seeing Pluto. And what does it look like? Well, kind of like the moon. We expected that. But there is that huge smooth section there in the south. That’s called Sputnik Planum. It is the western half of the Tombaugh Regio — Pluto’s “heart.” And it appears to be a glacier made of frozen nitrogen — with notable amounts of carbon monoxide and methane.

We also see on the edges of Sputnik Planum craters that have been filled in with this frozen ice. There is some speculation that below the surface (where it is warmer), there may be a layer of liquid nitrogen. The temperature on the surface of Pluto is -390°F — 39 K. Clearly, Nitrogen is solid there. At Earth’s surface pressure (which is fairly low), it becomes liquid at a balmy -346°F — 63 K. So we might be seeing actual geological activity, but instead of molten rock, it would be molten Nitrogen. It’s very cool — and bizarre to imagine.

Pluto HazeThe frozen nitrogen is constantly sublimating (turning directly from solid to gaseous form) into Pluto’s atmosphere. But it is in equilibrium, so the atmosphere is depositing onto the surface at the same rate. The atmosphere is made up of the same three compounds found in the ice: Nitrogen, carbon monoxide, and methane. Of course, there isn’t much atmosphere: just 0.001% as much as we have here on the earth. But still: notable. Plus: because of the effect of methane, the atmosphere gets warmer as you go up in the atmosphere (like in the Earth’s stratosphere), so that 6 miles up, it is 65°F warmer.

In addition to this, Pluto’s atmosphere has two distinct haze layers. One is about 30 miles from the surface, and the other at 50 miles. This is what we see in the image on the right. This was shot just seven hours after the close approach to Pluto. The sun is behind Pluto, so we are seeing the atmosphere back lit. What’s happening in the atmosphere is similar to what goes on in our own. Methane is broken down by ultraviolet light. It’s parts are then combined into more complex hydrocarbons like ethylene and acetylene. As they sink, they become solids and create the haze.

We will be learning more and more as time goes on. Every few days, I find myself checking on what new information is available. That’s a bit obsessive. But I’m sure as the years go by, we will continue to be surprised. I never liked the mystery of Pluto. Just knowing that there was some space rock flying around out there didn’t inspire me. But now that we are learning what’s really going on with the little world, it’s very exciting.

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