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jdmack
2006-Apr-24, 04:41 PM
Here is a portion of a hi-res photo of Mars that I took from the Astronomy Picture of the Day website:

http://www.stage2.com/mars.jpg

I have placed a black frame around a small feature. Because the photo is hi-res, it is possible to zoom in on this feature quite a bit.

My question is - what is it? OK, not really "what is it" but "why is it." It appears to be a crater, but it has a much smaller diameter than other prominent craters on Mars. Also, it is either much deeper or has significantly higher walls than most other craters. I am presuming that lack of sunlight is the reason for it being much darker. It almost looks like a bullet hole.

What would cause a crater to form like this? Or are there lots of craters like this on Mars? In the original photo (http://antwrp.gsfc.nasa.gov/apod/ap060410.html - which you have to download to see in its entirety) there is only one other crater like this near the top of the photo, so they seem arae to me.

J. D.

antoniseb
2006-Apr-24, 06:01 PM
I looks like a crater which is newer than the one around it, and that the crater interior has a darker substance in it than the ones around it (not re-dusted).

aurora
2006-Apr-24, 10:30 PM
Looks like some dark material got thrown out of the crater when it formed.

Unless it is just shadow, maybe there was some darker material under the surface at the spot where the object hit.

wollery
2006-Apr-25, 04:30 PM
It's just newer than the other craters, so it has sharper edges. Remember, Mars does have an atmosphere, even if it is tenuous, and its regular dust storms will erode features like crater lips.

In fact you can give relative ages to the craters in that photo;
The one you highlighted is the youngest, the crater lip is sharp and you can still see rays of dark ejecta.
The next youngest is smaller, slightly down and to the left, it still has fairly sharp edges.
There are quite a few small, fairly young craters dotted around.
The larger crater up and right of the one you highlighted is intermediate age, the edges aren't as sharp.
The really big crater up and left is older still, a lot of the lip feature is gone.
The oldest obvious crater is fairly large, located to the far left edge of the photo, about halfway down. It's been almost entirely eroded away.

Cool photo! :)