abstract:The Caloris Basin, also called Caloris Planitia, is a large impact crater on Mercury about in diameter, one of the largest impact basins in the solar system. Caloris is Latin for heat and the basin is so-named because the Sun is almost directly overhead every second time Mercury passes perihelion.
A few craters, such assomeinthehugeCaloris Basinimpactfeaturevisible on the upper right, appear unexpectedly to be ringedwith adarkmaterial, the nature of which is beingresearched.