$50 for Correctly Guessing the Number of Craters in this Image
Just kidding, there's no $50 prize. But counting craters on Mercury is a serious job, as the density of craters on the surface of a planet can be used to indicate its age; the more craters present, the older the surface. Although this technique is commonly used on planetary bodies throughout the Solar System, crater counting on Mercury is particularly challenging. Secondary craters are formed by debris thrown out during an impact, and are often big enough to be confused with primary craters. Their inclusion in crater-counting studies, however, would skew derived age results for a surface, making it appear older than it really is, and so care must be taken when deciding which craters to count, and which to leave out.
Date acquired: November 05, 2012
Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington