Irregardless isn’t it interesting that there is another similar scar so close… See my observation on yesterday’s triple hit.

I thought it didn’t matter the angle of the impact, craters were always circular? Or is that only when above some certain impact velocity?

You are right. This is how we are able to deduce that the impactor fragmented before it hit. The pieces hit close enough together that the impacts did not form separate overlapping craters, but instead one elongated feature, as the individual craters merged.

The form of this impact feature strongly suggests it traveled from the narrow end and plowed toward the fat end (right to left in the top image). Low-angle impact simulations bear this geometry out: when an impactor first makes contact with the surface, only a relatively small portion is sheared off, but the rest of the impactor is bouyed for a time by the energy released beneath it. But it continues to lose energy and gradually plows out a widening ‘channel’ until its bulk is consumed. The fact that one sees smaller elongated scars that are aligned with the main feature’s exclusively beyond the fat end (and no evidence of such beyond the narrow end) indicates secondary or briefly surviving impactor debris being cast forward from the main impact.

This is hardly new to impact science: one can see prominent twin rays extending beyond the famed lunar crater pair Messier and Messier A, located in Mare Fecunditatis. If you have a six-inch or larger telescope, have a look at it! Or look at the images in this well-illustrated Wikipedia article:

http://en.wikipedia.org/wiki/Messier_(crater)

One popular interpretation is that a shallow-angle strike by an impactor produced the highly-elongated Messier, and that at least part of it rebounded to create the complex form of Messier A (possibly with an initial gouge produced by one mass followed ‘almost immediately’ by another portion that came down onto the foot of the secondary gouge after it was lofted into a slightly higher ‘hop’) casting glassy material in jets further down-range to produce the twin rays.

But another fascinating feature of this complex are rays extending in narrow ‘wings’ perpendicular to the long axis of the main elongated Messier (which is also the brighter of the two in terms of albedo, indicating that it was almost certainly created with higher impact energy than its down-stream companion Messier A was).

The Mars analogs which Phil has featured in the last few days also have such perpendicular ejecta ‘wings’ – except this much larger one shown here (captured by Mars Express released last year) has a LOBATE terminus indicating fluid flow, stronglysuggesting the presence of a substantial reservoir of subsurface water ice – an unmistakably Martian habit and ubiquitous on Mars. You can see such lobate forms around a number of the larger circular craters in the same image.

LOL.

But *which* Enterprise are you meaning?

This one? :

http://www.youtube.com/watch?v=xeLqsvFO31o

Or this one? :

http://www.youtube.com/watch?v=vdvlLfqUJsQ&feature=related

Or maybe even this one :

http://www.youtube.com/watch?v=CU6t-bk_sqc&NR=1

perhaps?

They’re almost perfectly aligned,

What are you smoking, it seems nifty strong!? Rulers gives ~ 60 deg to ~ 70 deg ellipse long axis alignment to the W-E axis.

As to what happened to the dirt: duh, Phobos and Deimos.

“I wonder, could Mars once have had a third small moon? Perhaps in an eccentric orbit with a rather low Perigee (er, Periareion)?

Possibly; this is a good explanation for this crater, though not the only one: could also have been produced by a very oblique asteroid/cometary impact.

“If so, will Phobos one day create a similar gouge?”

Yes, in several tens of millions of years probably. It’s decaying orbit will be quite circular, with a smaller and smaller radius…

—–

I was about to post that too. Much clearer in the linked image, the cliff seems to be a much larger structure with its own continuity not something caused by this impact. Almost looks as if the impactor was traveling at such a low angle that it caught the lip of the cliff as the first point of impact. That seems a little more plausible than the second interpretation that sprang to mind, which is that it was traveling the opposite direction, also at an exceedingly low angle, and lost contact with the ground where the cliff dropped away, then impacted again further out, creating the other elongated crater that’s visible in the linked image. Probably I’ve seen too many Road Runner cartoons…..

For simplicity sake let me call the multi-impact crater pictured above “Crater A” and the second multi-impact crater that BA mentioned “Crater B.”

I’m no planetary astrophysicist, but I suspect that crater B is considerably older than Crater A. Crater B shares the smoother bottom that the majority of the craters in the area have while Crater A does not, suggesting that Crater B was likely part of the Late Heavy Bombardment phase that ended about 3.6 billion years ago (so as a non-specific answer @ crf [#20]: younger than that).

Considering the amount of energy that must be expended in order to excavate a crater, it seems unlikely to me that Crater A was formed in the main by a single body that “skipped” across the surface of Mars. Remember that the body that forms an impact crater is much smaller than the crater itself, and that the kinetic energy of the impact largely destroys that body. For example: the mile-across Meteor Crater in Arizona is thought to have been formed by a meteorite that was about 150 feet across, and while traces and chunks of it have been found the majority of the meteorite apparently was vaporized in the impact.

We can also see individual craters overlap. The one at the wide end has apparently formed after the biggest crater. The piece which has done the wide end crater flew higher and therefore traveled further and hit later.

I wonder, could Mars once have had a third small moon? Perhaps in an eccentric orbit with a rather low Perigee (er, Periareion)? If so, will Phobos one day create a similar gouge?