http://esamultimedia.esa.int/images/..._Eos_ortho.jpg

There are a series of craters I am having trouble understanding. They look like this OOO, pointing to 5 o'clock

Go to the very bottom right of the image and go up and they are just right of the big crater.

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Round...everything is always round!

Could have been a meteor or asteroid that was in 3 pieces before it hit, and were at just the right distance to make the craters distinct.

Yup, they look like they all formed at about the same moment, since the border between them looks like it is midway (if one of them was the newest, then it would have overlain the others).

Might have been a comet that had just started to break apart, or an asteroid with moons. Something that was breaking up.

By the way, that is an amazing image!

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"Arrrgh, the laws of physics be a harsh mistress!" -- Bender

I agree with you, Aurora, it's truly an amazing image!!! The craters did most likely all form at the same time as we see no overlapping of any that might have arrived at different times.

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When an object without a lot of tensile strength orbits a body inside a certain radius (that radius is called the Roche limit) tidal forces will break the object up.

So it works like this, if you have an asteroid made out of one big chunk of iron, then obviously it's going to stay in one piece and make one crater. However, imagine you have an object made of boulders and held together only by its own gravity. When that object gets inside the Roche limit, it will break up. But that doesn't mean it explodes or anything. The forces that break it up are the same forces that cause tides on Earth, and if you remember from your middle-school science class, there is a high tide on the side of the Earth that faces the Sun (or the Moon) and *another* high tide on the opposite side of the Earth. Two high tides. When you stand back and look at it, those two high tides make it look like the Earth is being stretched out, flattened. The same thing would happen to our hypothetical boulder object. It would stretched out into a straight line of individual boulders. There is still some gravitation attraction between the objects though. They tend to stay together in that straight line.

The textbook example of what I just described is comet Shoemaker/Levy 9. I know you've seen pictures of it.

When an string of objects like that finally enter the atmosphere and hit the planet, they make a long line of craters like the ones in the picture. If there are a lot of objects, they actually end up being sorted by gravity. The smallest, lightest objects move the farthest, and you'll see a very cool series that looks like this:

..ooOoo..

There is very little ejecta material around most of the craters. Has it all been blown away?
Is this land formerly surrounded by sea possibly?

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Round...everything is always round!

I don't think a sea. However, the image shows a lot of activity -- slumping, runoff, possibly underground melting and release of water.

Perhaps the surface was somewhat soft, like permafrost that melted.

__________________
"I'm as accurate as any psychic. And I'm a cartoon!" -- Squidward

"Arrrgh, the laws of physics be a harsh mistress!" -- Bender

But if Mars did possibly, maybe, theoretically have seas, (as some suggest) is this the kind of shoreline/coastline we would see? (Sea?)
There appears to be quite a lot of fluvial 'looking' erosian channels/gullies etc.

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Round...everything is always round!

Right, which is why it does not look like an ancient seabed.

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"I'm as accurate as any psychic. And I'm a cartoon!" -- Squidward

"Arrrgh, the laws of physics be a harsh mistress!" -- Bender