Does Pluto Have a Subsurface Ocean?

As it turns out, apparently you can't go five feet in the outer solar system without hitting a subsurface ocean. Europa's got one, Enceladus has one, and Titan, Ganymede, and Callisto probably have them. That's not even mentioning the list of objects that may have them, according to models of radioactive decay. Here's a list of those.

If you're observant (or read the title of this post), you'll notice Pluto on there. I've written about Pluto on several occasions now, as data from New Horizons slowly filtered through. The data return is done, but we still have a lot of things to learn from it. Like this, for example. Based on research of Sputnik Planitia, otherwise known as Pluto's "heart", it is very likely that Pluto possesses a subsurface ocean.

It is believed Sputnik Planitia was once a vast impact basin filled with a layer of nitrogen ice about 6 miles thick. That's fine, but what's interesting is that Sputnik Planitia is oriented almost directly opposite to Charon, the smaller partner in the Pluto-Charon double planet system. This position on Pluto's tidal axis is probably not a coincidence. After the impact, the basin filled up with nitrogen ice. This happened slowly, but as this gigantic mass of ice formed, it changed the shape of the planet, causing the basin to slowly wander towards its current, more natural position on the tidal axis. And as it moved, a series of faults and fractures would have appeared across the surface. And Pluto has these faults and fractures.

Where does the subsurface ocean come in? The sort of movement that Sputnik Planitia has undergone would be impossible without a subsurface, the model depends on it, and observations seem to back up the model. The model predicts faults and fractures, and there are faults and fractures.

Further proof comes from a second study. Those scientists calculated the odds of Sputnik Planitia forming in it's current spot at about 5%, and so also believe the feature has moved over time. They found that the impact which formed the basin would have weakened the crust, bringing the subsurface ocean close to the surface. This along with the accumulation of nitrogen ice would essentially roll the (dwarf) planet around. Without the liquid water, the ice of Sputnik Planitia would have to be several times thicker than currently believed, and that doesn't match up with our observations.

So there we have it. Pluto: likely possessor of a subsurface ocean. It's still not a planet though.

Pluto: The Saga Continues

Yes, it's time for another installment of big Pluto news. New Horizons is still sending back data, and will be for several months. As that data comes in, we learn more and more about this surprisingly complex little world. A group of five studies was recently published in the journal Science about Pluto, so let's take a look at what scientists have learned.

The first piece of news is that Pluto's surface has a lot of variation in which type of ice is dominant. There are areas which are mostly methane ice, areas which are mostly nitrogen ice, and areas which are mostly water ice. Nitrogen ice is dominant in the flat, craterless plains, while water ice is dominant in the mountainous regions, reflecting their characteristics at the very cold temperature Pluto sits at. Water ice is very rigid and behaves almost like rock does on Earth, while nitrogen ice is much less tough and is able to flow, much like our glaciers on Earth. Indeed, this sort of distinct differentiation in material most closely resembles Earth, where the surface is separated by areas dominated by water and by rock.

Another study focuses on the geology of Pluto, especially Sputnik Planum, the vast, nitrogen ice dominated region in the southern hemisphere. The plain is located on an ancient impact crater, and its smooth, craterless surface contrasts sharply to areas with a heavy crater density scientists were likely expecting all over Pluto, and to areas with an intermediate crater density. Small bodies like Pluto should have frozen solid all the way through billions of years ago, but something is causing Sputnik Planum and much of the surface to refresh itself, though what that mechanism is remains unknown. The same study also demonstrates that Cthulhu Regio is covered in tholins, an organic molecule that has turned the area a deep red. The tholins likely drifted down from the atmosphere and the mountains Wright Mons and Piccard Mons. These are big mountains, Wright Mons is 2.5 miles high and Piccard Mons is 3.7 miles high, and likely formed through cryovolcanism.

Pluto's atmosphere was the focus of a third study. It's a bit less interesting, but it turns out that the Plutonian atmosphere is significantly colder than what was predicted before New Horizons' visit. Because of this, the particles of the upper atmosphere are much less energetic, which in turn means the atmosphere is losing gas at a much slower rate than what was anticipated. Initial estimates were off by about a factor of 5,000.

Don't worry, Pluto's five moons weren't forgotten in all this new research. Pluto's biggest moon Charon is actually quite a bit different from Pluto, and closer in line to what scientists were expecting. There is some very dramatic topography, but on the whole, Charon is a dead world, and has been for about 4 billion years. Its surface is mostly water ice, and is lacking significant amounts of methane and nitrogen ice like Pluto has. Why this is the case is unclear. An additional study examined the 4 smaller moons, which are much more reflective than more typical Kuiper Belt objects, and move very chaotically. This bolsters the theory that the moons are bits of debris that were thrown off in an enormous collision early on in Pluto's history, and the 4 moons are survivors that have managed to escape being sucked up by either Pluto or Charon.

Credit: NASA/John Hopkins University Applied Physics
 Laboratory/Southwest Research Institute

In news unrelated to the Science studies, scientists recently announced that as recently as 800,000 years ago, Pluto likely had a much thicker atmosphere, more substantial than even Mars. Right now, the Plutonian atmosphere has a pressure about 1/100,000 that of Earth's, and this is likely what it usually is. However, Pluto has a axial tilt of about 120 degrees, and as the planet's tilt slowly undergoes procession, there are certain times when the amount of solar radiation in areas with lots of volatile ices goes up dramatically. The resulting outgassing would thicken the atmosphere so that the pressure would increase to about a tenth of Earth's. This is significantly thicker than the Martian atmosphere, and potentially thick enough to allow liquid nitrogen to flow freely on the surface. A thicker atmosphere with liquid nitrogen streams and ponds would explain a series of unusual surface features, such as empty channels similar to those seen on Mars, and a flat, icy area that resembles a frozen pond. The possibility of a thick atmosphere and the existence of a nitrogen cycle similar to Earth's water cycle, even if temporary and limited, on such a tiny, cold world seems pretty far-fetched, but ever since New Horizons flew by, Pluto has surprised us. This batch of new science has made Pluto that much more interesting.

It's still not a planet though.

A Ninth Planet for Our Solar System?

Yes, that's right, after 10 years, the International Astronomical Society have realized their mistake and are reinstating Pluto as the ninth planet. It's a controversial decision in the astronomical world, but the IAU has recognized the public popularity of Pluto, especially after the New Horizons visit, and astronomers now feel that an exemption should be made for Pluto.

Uhhh, no. Did I have you going? Probably not.

So, yes, scientists have announced that there is likely a large body very far out in the solar system, hundreds of AU away. It obviously isn't official yet, but this is some very interesting news. The hypothetical planet would likely be about 10 times more massive than the Earth and would orbit about 20 times further away then Neptune. The evidence for the existence of this object, since we haven't actually seen anything, is that the orbits of 6 Kuiper Belt objects seem to be heavily influenced by something. The orbits all point in the same general direction, even though the objects, including the dwarf planet Sedna, are moving at very different speeds.

If you recall your astronomical history, you'll remember that the search for Neptune commenced because of perceived inconsistencies in Uranus' orbit, and that the search for Pluto occurred because of inconsistencies in Uranus' and Neptune's orbits. So, as with most extraordinary discoveries, it's important not to jump to any conclusions. But I do find it interesting that a few months back, scientists hypothesized the existence of a fifth gas giant in the early solar system which was cast out due to interactions from an early Jupiter or Saturn. This hypothetical planet would have been an ice giant, like Uranus and Neptune. The new "Ninth Planet" is also almost certainly an ice giant which probably did not form that far out in the solar system. Interesting how this works out, isn't it? I'm expecting to hear more about this in the future.

So, What's The News From Pluto?

It's been a while since I've mentioned Pluto. New Horizons has been slowly but surely sending back data and some absolutely spectacular images, revealing a world way more complicated than anyone could have predicted.

First off, there's the pictures. The most recent ones show a 50 mile wide strip of Pluto's surface extending on for hundreds of miles. The resolution is about 300 feet. Somehow, geology has crafted great mountains of ice thousands of feet high, as well as rugged badlands extending for miles.

Credit: NASA/JHUA/SwRI

Credit: NASA/JHUA/SwRI

This image is a particular favorite of mine. It's a picture from the other side of Pluto, and I don't know. There's just something about it that appeals to me. The way the haze fades away, the contrast between the mountains and the plain, it's a great image. I have it as my wallpaper on my work computer.

Credit: NASA/JHUA/SwRI

Oh, in case you were curious, if you were standing on the surface of Pluto and looked up, you'd see a blue sky, courtesy of reactions between methane, nitrogen, and sunlight.

Credit: NASA/JHUA/SwRI

In the picture below, the mountains imaged have a very odd texture, almost like tree bark. There was a guess hazarded as to their origin, but basically, we have no idea how they formed. Looks cool, though.

Credit: NASA/JHUA/SwRI

Oh, here's some actual science now. Scientists believe that based on the lack of cratering and the replenishing of nitrogen in the atmosphere, Pluto was almost certainly recently geologically active. It may even still be active today, courtesy of liquid water laced with ammonia. New Horizons even has images of potential cryovolcanoes.

I think that's all for now. Hopefully my next Pluto update won't take so long.

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.

New Horizons and Orion

On their own, I'm not sure either of these stories are worth a post, so I'll go ahead and combine them.

The New Horizons space probe woke up from a long hibernation this weekend. It's on it's way to Pluto, and will fly by on July 14, 2015. It will be, of course, the first spacecraft to visit Pluto, and the first to obtain any sort of detailed image. Even the most advanced telescopes on Earth or in orbit can barely make out any detail. That's definitely something to look forward to this summer.

In a follow-up to my last post, the Orion spacecraft, NASA's new manned crew capsule, underwent a successful first test launch a couple of days ago. I have to confess, given how many rockets have exploded during launch recently, I was a little worried about Orion. I'm not sure the manned space program could take a setback like that. Orion needs to work, and it needs to work well. At least it's gotten through it's first test just fine.

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