An image from Mars Global Surveyor in orbit above Mars:
The crater must be very large. Does there appear to be a perfectly spherical object in the crater? Has this image been discussed before? The site hosting that copy of the image acquired it from here:
Mars Global Surveyor Image Collection
The original is exactly the same but includes a larger area. In some regional images there are some slightly similar features, but none as notable as the feature above. What are we looking at?