Ceres Craters: Investigating NASA's Dawn Animation

[Borek]

Using images from Dawn NASA has produced this fascinating animation of Ceres:



What struck me while watching is the fact that most craters look almost perfectly round in shape. Perhaps it is the same for other bodies, I just never thought about it earlier. Intuitively I would expect the crater shape to depend on the hit angle, and hit angles to be mostly random. Sure, few craters are oval, but the majority looks like a result of a hit perpendicular to the surface.

Obviously gravity can skew the distribution of hit angles, but somehow I doubt it would eliminate tangential hits.

What am I missing?

 

[Drakkith]

Not sure. They don't look too terribly different from craters on the Moon to me.

 

[jaormsby]

If anything, an asteroid is more likely to collide with a celestial body the more its orbit overlaps with the orbit of that body. I'm no expert but it would stand to reason that a considerable number of asteroid impacts would occur when the celestial body is lined up with the asteroid and they're traveling in roughly the same direction.

 

[David Plunk]

I've never replied to any forum on any website before, but I think I can answer this.
There has to be quite a few strikes at slanted angles, even if the asteroids are traveling in the same general direction. Here goes my theory: Because the impacts between celestial bodies are usually at very high speeds, I believe there is an explosion created on impact that "outweighs" the inertial forces of the object impacting. And this explosion is directed in all directions. This could create a circular crater even if striking at a very slanted angle. When the comet Shoemaker-Levy fragments hit Jupiter, they created circular explosions by just hitting clouds! Okay, atmosphere. Your oval craters are probably the lower speed impacts at an angle and speed that didn't create much of an explosion, or a pair of close objects that did.

 

[Janus]

I've never replied to any forum on any website before, but I think I can answer this.
There has to be quite a few strikes at slanted angles, even if the asteroids are traveling in the same general direction. Here goes my theory: Because the impacts between celestial bodies are usually at very high speeds, I believe there is an explosion created on impact that "outweighs" the inertial forces of the object impacting. And this explosion is directed in all directions. This could create a circular crater even if striking at a very slanted angle. When the comet Shoemaker-Levy fragments hit Jupiter, they created circular explosions by just hitting clouds! Okay, atmosphere. Your oval craters are probably the lower speed impacts at an angle and speed that didn't create much of an explosion, or a pair of close objects that did.

Your intuition is correct. The crater is caused by the explosion of impact and the angle of the strike has little to do with it. Only in cases of an extremely shallow impact angle will the crater deviate from being nearly circular. In this case, the "impact" is more of a "graze" with the impact energy spread along a line and creating a elongated crater.

 

[Borek]

Thank you guys, case solved :)