Monday, 27 June 2011

Ice Blobology in the Kuiper Belt

Back in 2006, just before my interest in astronomy was rekindled by Galaxy Zoo, a spacecraft launched. It was called New Horizons. On 14th July 2015, it will reach a dwarf planet foursome: Pluto, Charon, Nix and Hydra. One of the things it will do there is use a spectroscope to examine Pluto's atmosphere - and see if Charon has one too, though that is another story. Its spectroscope, incidentally, is called Alice, which unlike CERN's is a whim not an acronym. The Rosetta spacecraft has an Alice on board too.

Diagram of New Horizons, from the BBC

So at the moment, New Horizons is about halfway to Pluto. But once it's done that job, it's got a whole Kuiper Belt to explore - and NASA is employing a wonderfully democratic way of choosing where to send it next: zooites.

The Kuiper Belt is the part of our Solar System that lies beyond Neptune. In 1943, a man named Kenneth Edgeworth speculated that beyond Neptune, any matter would have been too widely distributed to condense into more planets. Gerard Kuiper wrote in 1951 that a belt of small bodies would have been around in early times, but - because he believed, as many people did at the time, that Pluto is the size of the Earth, when we now know it is less than a fifth the size of the Moon - he did not think it would be there today. He is far from the first scientist to be remembered for something he did believe in! If Pluto had been as massive as Earth it would have done what actual planets do, that is, gravitationally scoop up or scatter all the other matter in its orbit.

The Kuiper Belt extends out to roughly twice as far as Neptune. It's thought to be the origin of a some comets, as even materials such as ammonia that we think of as gas are solid so far from the Sun. It is not the same as the Oort Cloud, which pretty much extends halfway to the next star - a sort of Sun-bubble, if you like. It's believed to be of a complex structure - Neptune's gravity, and resonances, and the fact that it maintains roughly the same disk shape as the rest of the Solar System, bunch up areas of the matter together. But, being of bodies so small, and so far from any source of light or heat, it's not been very easy to study. In fact, it was only really discovered for certain in 1992! This discovery involved painstaking poring over what were doubtless faint fuzzy images by two astronomers named David Jewett and Jane Luu, working in Hawaii in the late 1980s.

Technology has moved on since then, and now there are thousands of ground-based images of the Kuiper Belt. The Zooniverse has set its - what is it now, 400,000? I keep losing count - volunteers to going through these images to find possible Kuiper Belt Objects. If all goes well, New Horizons will be able to explore one or more of them.

This project is called Ice Hunters. Here's a sampling for you:

You can read about the mission and do the tutorial and so on - but here's a quick overview of what to do with that image. How to tell what is a Kuiper Belt Object out of that lot? (Click to enlarge, by the way.)

Well, what happens with image like these is that the area is looked at twice, and two images produced - one positive, one negative. When the two are overlaid, if nothing has changed, the image should be consistent. But if something has changed, it will be obvious. This, incidentally, is how Henrietta Leavitt found her Cepheid variable stars - very plodding, detailed work indeed, when plates meant sheets of glass, spotted with black or white, and spectra about 2mm long.

In practice, you can probably see that it's not working quite that smoothly: all the white blobs that contain some black are background stars. But there are two (or more, if I've failed to spot them) pure white blobs. Here they are, marked out:

(PS if you're wondering why my Facebook tab has "aaaaaaargh" as its heading, it was because I was commenting on a dreadful joke made by Richard Wiseman. I'm so intellectual sometimes.)

You can go back and look at images you classified. Here's one of mine, which has another interesting object in it. It's on the lower right.

It probably looks like a wormy thing at this size. In any case, it's actually apparently three blobs stuck together. Just like in the Galaxy Zoo Asteroid Thread, asteroids move relative to the Earth, so their position changes. So we're keeping an eye out for asteroids too.

Very thin, hairy streaks tend to be cosmic rays, not asteroids. I got caught out a couple of times marking them before re-reading the tutorial and realising I shouldn't. Oh well - as with all the Zooniverse projects, the beauty of it is they get several people to classify each image, so just such mistakes get ironed out. And, added up, human eyes are much better at this than computers.

Another way I got caught out is by images like this one:

On the right there is a dark streak, which is full of pure white blobs. Whenever there are that many pure white blobs, they tend to be in just such a dark streak, and I've come to the conclusion that these must be where the subtracting has slipped and we're being shown just one plate. They're doubtless stars - otherwise, Kuiper Belt Objects would be all over the place. Which just goes to show how important it is to clean up all those pesky stars! That must take an awful lot of programming, which is still continuing judging by the fact that they've got a checklist where we can mark out what's wrong with the image on the right.

And, being very fond of paraedolia, I couldn't help but laugh at some of the silliness in many of Ice Hunters's images . . . look at this little man jumping around on the bottom left!

We also have doughnut eyes . . .

. . . and a lot of spaghettified bottles and heads in bubbles!

So who wouldn't want spaghettified bottles, heads in bubbles and a chance to help NASA decide where its spacecraft is going to go? There's already what might turn into a row about which is the best Zooniverse project on my Facebook page. Personally, I have a fierce, mindless, animal loyalty to Galaxy Zoo, for being my first, and the one I have looked after for four years (Chris and I joked in Chicago about how the baby is growing up and has to go to preschool!). But I think I might hang onto Ice Hunters better than I did the other ones I tried. We'll see. Sadly, there just isn't time to pay attention to them all.