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Vesta's cratering
Aug. 2nd, 2011 01:41 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
steorra(Cross-posted to my own journal)
Today's Astronomy Picture of the Day confirms something I'd noticed from looking at some of the early reasonably detailed pictures of Vesta. As I observed here, Vesta's southern region is not very heavily cratered. There are some craters on it, but they're not all-over-the-place-everywhere. At that time, I hadn't seen any good picture of the northern hemisphere to know whether it was similarly lightly cratered, but I suspected it was more heavily cratered, and as the APOD commentary says, it is indeed more heavily cratered.
Here's the APOD's commentary on the cratering:
Now, in general, the more heavily cratered a chunk of terrain is, the older it is. When new terrain is formed, it doesn't have any craters yet, and as time goes on, stuff smashes into it and it gets craters. So the older it is, the more time it's had for more stuff to smash into it and make more craters. It's a bit more complicated than that - in the early history of the solar system, there was more stuff around in space to smash into things, so the rate of cratering decreases as we get farther away from the early solar system. But still, it works out to the fewer craters a chunk of surface has, the newer it is. (I think crater size plays into the formula too, but I don't remember much about that.)
So the relative lack of craters in Vesta's southern half suggests that it's relatively recent terrain.
Even before Dawn got to Vesta, it had been proposed that Vesta's south half is shaped as it is because a large impact had basically knocked off a huge chunk of the southern hemisphere. It seems like a fairly obvious guess to make that the age of the southern terrain is an indicator of the age of that impact.
The APOD also mentions the grooves that encircle Vesta in the southern part of the equatorial region.
Pictures of Vesta from Dawn are available here and here.
There's also a NASA news conference video about Vesta from yesterday, but I haven't watched it yet.
Today's Astronomy Picture of the Day confirms something I'd noticed from looking at some of the early reasonably detailed pictures of Vesta. As I observed here, Vesta's southern region is not very heavily cratered. There are some craters on it, but they're not all-over-the-place-everywhere. At that time, I hadn't seen any good picture of the northern hemisphere to know whether it was similarly lightly cratered, but I suspected it was more heavily cratered, and as the APOD commentary says, it is indeed more heavily cratered.
Here's the APOD's commentary on the cratering:
Why is the northern half of asteroid Vesta more heavily cratered than the south? No one is yet sure. This unexpected mystery has come to light only in the past few weeks since the robotic Dawn mission became the first spacecraft to orbit the second largest object in the asteroid belt between Mars and Jupiter. The northern half of Vesta, seen on the upper left of the above image, appears to show some of the densest cratering in the Solar System, while the southern half is unexpectedly smooth.
Now, in general, the more heavily cratered a chunk of terrain is, the older it is. When new terrain is formed, it doesn't have any craters yet, and as time goes on, stuff smashes into it and it gets craters. So the older it is, the more time it's had for more stuff to smash into it and make more craters. It's a bit more complicated than that - in the early history of the solar system, there was more stuff around in space to smash into things, so the rate of cratering decreases as we get farther away from the early solar system. But still, it works out to the fewer craters a chunk of surface has, the newer it is. (I think crater size plays into the formula too, but I don't remember much about that.)
So the relative lack of craters in Vesta's southern half suggests that it's relatively recent terrain.
Even before Dawn got to Vesta, it had been proposed that Vesta's south half is shaped as it is because a large impact had basically knocked off a huge chunk of the southern hemisphere. It seems like a fairly obvious guess to make that the age of the southern terrain is an indicator of the age of that impact.
The APOD also mentions the grooves that encircle Vesta in the southern part of the equatorial region.
Pictures of Vesta from Dawn are available here and here.
There's also a NASA news conference video about Vesta from yesterday, but I haven't watched it yet.
