I agree that it is unlikely unrelated to the other two (it’s obviously significantly older than the two bigger ones, although there is a very small possibility that a smaller moon struck first and got swamped by the other two bigger strikes in the same event).

But it’s size and alignment has nothing whatever to do with determining whether it was associated with the other two. If it was another smaller moon in a 3-body system it could have had any position with respect to the other two at the time of impact. Alignment isn’t a necessary condition for a hypothetical pre-impact association.

And why should its smaller size not simply indicate a smaller moon?

In any case, Vesta’s gravity is too feeble, and typical relative velocities in the asteroid belt are too swift, for a single body loosely held together to have been separated by Vesta’s weak tidal gradient in the brief time of approach before impact. The multiple crater chains we see on the outer Galilean Satellites of Jupiter, for example, are thought to be caused by bodies that were stretched apart into a number of fragments by the tidal influence posed by their close passage by Jupiter before impact.

Think Comet Shoemaker-Levy hitting one of them in quick proximal succession in a near-single event: blam-blam-blam! like machine-gun fire before they separated very far from one another…instead of winding around and getting increasingly widely separated over many months and falling back to strike Jupiter as a long train of fragments over a period of days. Vesta just can’t exert the necessary tidal stress for long enough to do that to an impactor of typical composition just before it strikes. If it DID, the body would have to be composed of something like fluff, and fluffy fragments aren’t going to create such emphatic craters as these which were obviously produced by pretty energetic and nominally rock-dense impactors. They appear to be very much the same age, and I agree that the impactors responsible were a double asteroid.

http://darkerview.com/darkview/uploads/Astronomy/Astrophoto/CD22-64-09358-DC.jpg

(A bit to the top and right of Rupus Recta.)

You’d be surprised. Very frequently, especially in heavily cratered regions of Mars, this is the case where you can have a 10s-km crater overlapping a still-visible sliver of a smaller crater. I’m not saying that’s definitely the case here, but you should not dismiss it so quickly via your own argument from personal incredulity.

Ooh! Craters!

Pretty cool, eh?

Yup.

What would Vesta’s surface temperature be again – well below freezing I’d expect?

Great picture. Thanks BA & thanks to the Dawn team too.

I’m really looking to more from Dawn as well – especially from Ceres. Can’t wait for that.

***

“I consider it quite conceivable that the day may come when Ceres will be the astronomical centre of the solar system.”
- Page 66, chapter 5 “The World Ceres” in ‘The Tragedy of the Moon’ by Isaac Asimov, Mercury Press, 1973.

Once thought to be rocky, we now believe Ceres may contain 200 million cubic kilometres of water in its mantle. This is more than the amount of fresh water on the Earth.
- Page 10, “Ceres may be a failed miniplanet” by Jeff Foust in Astronomy Now magazine, November, 2005.

“… he had left out a planet. It was not his fault; everyone leaves it out. I leave it out myself when I list the nine planets, because it is the four-and-a-halfth planet. I’m referring to Ceres; a small but respectable world that doesn’t deserve the neglect it receives.”
- Page 63, chapter 5 “The World Ceres” in ‘The Tragedy of the Moon’ by Isaac Asimov, Mercury Press, 1973.

I’m willing to bet the area to the bottom right of the larger crater looks the way it does because of variations in the terrain (vestain?) that existed before the impact. Look at the way this area lines up with the “grooved” striations running in a parallel row down and to the right. Notice how the linear ridge, marked by shadow, within the crater lines up almost exactly with those broad features. Coinkidink? Prolly some looser material within the grooves went kablooie when the rock hit, while the ridge of more solid material stayed relatively intact.

That’s my story and I’m sticking with it. Until something better is suggested, at which time I will deny all knowledge of it and claim my computer was hijacked by a bitter nerd from Anonymous.

Phil’s comment, in his edit, about the softer rim seems to apply to the large two–the lower right one seems younger. It also seems to overlap and overlay the left upper one. So, not a double impact, but two separate impacts, seems to me. The latest seems to have “flowed” to the right a bit too.

As to the bottom-right “collapse”… Is it possible that the asteroid that struck that position was odly shaped with maybe a big crater of its own at that position? Something like a “donut-hole” with a fair-sized bite taken out of it? It would seem that could possibly explain a softer rim at that location… The bite point wouldn’t have as much energy to impart into that area, would it?

AWESOME pic!