Here's a look at some of Mercury's most enduring mysteries. In the words of Messenger science team member Robert Strom, "The best is yet to come. What you're seeing here is just the tip of the iceberg."
But there are important differences between Mercury's craters and the moon's. For one thing, some craters on Mercury seem to be shallower than similar-sized craters on the moon, although the scientists must investigate further Messenger data to see if this trend holds across the planet.
This image shows the littered surface of Mercury, where some craters are secondary, formed when material displaced in one impact lands nearby and forms another crater.