[X] My Assistant

[djellison]

Look at the MI campaign on this puppy It's got to be a 4 x 4 frame MI mosaic

http://qt.exploratorium.edu:16080/mars/spi...cam/2005-04-28/

Doug

[Burmese]

I wonder how this rock picked up that tidy circular impression?

http://marsrovers.jpl.nasa.gov/gallery/all...I4P2564L7M1.JPG

[dvandorn]

I wonder how this rock picked up that tidy circular impression?

http://marsrovers.jpl.nasa.gov/gallery/all...I4P2564L7M1.JPG

There's always one good explanation for tidy circular impressions -- craters. In the absence of any other data, I'd guess it's a very small crater from a very small impactor.

I bet the rock is pretty soft or unconsolidated, though, to record a crater so nicely without being blown to bits by such an impact...

-the other Doug

[JRehling]

I wonder how this rock picked up that tidy circular impression?

http://marsrovers.jpl.nasa.gov/gallery/all...I4P2564L7M1.JPG

There's always one good explanation for tidy circular impressions -- craters. In the absence of any other data, I'd guess it's a very small crater from a very small impactor.

I bet the rock is pretty soft or unconsolidated, though, to record a crater so nicely without being blown to bits by such an impact...

-the other Doug

Any impactor small enough to make a crater that small would certainly have burned up in the martian atmosphere. This is the sort of impact feature that may exist on the Moon, but never Mars.

[Jeff7]

I wonder how this rock picked up that tidy circular impression?

http://marsrovers.jpl.nasa.gov/gallery/all...I4P2564L7M1.JPG

There's always one good explanation for tidy circular impressions -- craters. In the absence of any other data, I'd guess it's a very small crater from a very small impactor.

I bet the rock is pretty soft or unconsolidated, though, to record a crater so nicely without being blown to bits by such an impact...

-the other Doug

Any impactor small enough to make a crater that small would certainly have burned up in the martian atmosphere. This is the sort of impact feature that may exist on the Moon, but never Mars.

They've found what look like tiny craters at Opportunity's site. Sure, if it's tiny when it enters the atmosphere, the object will disintegrate quickly. But if it's large enough, a small portion of it could make it to the surface.

I place my bet that it's simply a random formation - just like how we see shapes in the clouds, we happened upon a formation that has a round imprint on it.

[JRehling]

I wonder how this rock picked up that tidy circular impression?

http://marsrovers.jpl.nasa.gov/gallery/all...I4P2564L7M1.JPG

There's always one good explanation for tidy circular impressions -- craters. In the absence of any other data, I'd guess it's a very small crater from a very small impactor.

I bet the rock is pretty soft or unconsolidated, though, to record a crater so nicely without being blown to bits by such an impact...

-the other Doug

Any impactor small enough to make a crater that small would certainly have burned up in the martian atmosphere. This is the sort of impact feature that may exist on the Moon, but never Mars.

They've found what look like tiny craters at Opportunity's site. Sure, if it's tiny when it enters the atmosphere, the object will disintegrate quickly. But if it's large enough, a small portion of it could make it to the surface.

I place my bet that it's simply a random formation - just like how we see shapes in the clouds, we happened upon a formation that has a round imprint on it.

If something large is worn down to something small, it won't be moving fast enough to create a "crater" when it hits. For example, the meteor spotted by Opportunity. If an object that size had hit the Moon, it would not be sitting there intact. By surviving entry, it is going too slow to vaporize the target area.

[dvandorn]

  If something large is worn down to something small, it won't be moving fast enough to create a "crater" when it hits. For example, the meteor spotted by Opportunity. If an object that size had hit the Moon, it would not be sitting there intact. By surviving entry, it is going too slow to vaporize the target area.

Meteors sometimes explode into fragments as they pass through an atmosphere -- even iron meteors. Especially if they enter at a highly oblique angle and experience a relatively long duration heating event.

If a meteor explodes, say, 500 meters above the surface and propels pieces in all directions, some few pieces will have their forward/downward motion greatly reduced,and will simply fall out of the sky from there. Falling from 500 meters, such a piece will hit and sit on the surface, just like we've seen at Meridiani. Happens all the time on Earth.

At the same time, a smaller chunk could be propelled from 500 meters on to the ground and make a tiny little crater. There would probably be a footprint whose far end would have a range of craters made by the chunks that survived and continued to the ground, and whose back end was made up of chunks of meteor sitting on the ground, relatively unscathed.

Yes, it probably happens pretty rarely that a chunk of meteor is slowed down by explosion dynamics and ends up sitting on the ground like it was set there by some giant's hand. But even things that happen *extremely* rarely can be commonly seen if you wait a few billion years...

-the other Doug