Suisei Planitia is a large basin on Mercury

Mercury (planet)

Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...

. Ghost craters

Impact crater

In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...

 are unusual forms that occur in the Suisei Planitia. They are buried and rounded in profile, with only their rim crests rising above the surrounding smooth plains. It has been suggested that the smooth plains that Suisei Planitia is part of (Caloris Planitia) might be ejecta from Caloris that were melted by the impact. The name for this Planitia was approved in 1976.