Object found in Kuiper Belt suffered impact

18 March 2007

Interview with

Mike Brown California Institute of Technology

Chris - Mike has found an object at the edge of the solar system in the Kuiper Belt. Tell us a bit about this object Mike?


Mike - This is one of those very interesting things that you stumble upon without having any idea that its there. We found this very interesting object a couple of years ago, its out in space beyond Neptune. Its bigger than Pluto in one dimension but its actually half the size of Pluto in another dimension - its like the shape of an American football that's had some of the air let out if it and has been stepped on, it spins end-over-end every four hours. What we have recently found is that the object was smashed by something else that was maybe half the size of Pluto, maybe four billion years ago and that's what led it to rotate and the interesting thing we finally found is the other chunks that came off it after it got smashed.

Chris - So where have they gone? You'd anticipate that if something was smashed into by something the size of Pluto that the remnants would disappear.

Mike - Two of the little pieces went into orbit around this object, the other six pieces that we found are not in orbit around the object but they are in orbit around the sun. They got ejected from the object itself but they didn't get ejected fast enough so you can still see them in the vicinity of this object out there past Neptune.

Chris - How do you know that those objects are actually from that parent object that first got smashed in to and not just other debris that from nearby?

Mike - The only way that we know that we realise that these are chunks from the original body is that they're all made of exactly the same material and there's nothing else that we've found that's made of exactly the same material. When we found the first object we thought - Wow there's this one big body that rotates really fast and is shaped like a football, then we found a few more smaller ones and thought what's going on? Then it dawned on us that these are in orbit around the sun, if you trace their orbits back you can see that they intersect.

Chris - So that's the outer solar system, but does it give us any clues about the configurations you see closer in nearer to Earth?

Mike - The fascinating implication for the inner solar system is that this collision that happened probably four and a half billion years ago was right at the beginning of the solar system. This collision happened to occur by chance in a region of the solar system that is close to being unstable - that is if you put something in orbit there it won't stay in orbit for a very long time. This means that all of the fragments from this collision have had the chance to become unstable and when they've become unstable they work their way into the inner solar system and they become things that we call comets today. So its very likely, in fact inevitable that some of the comets that we have seen in our lives have been from this actual collision. It must also be that some time in the past chunks of this very large object that broke apart have landed on the Earth.

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