On the left, the floor of the Moon's Mare Ingenii, "the Sea of Cleverness," as seen by the Lunar Reconnaissance Orbiter. On the right, Mercury's Caloris Planitia, "the Plains of Heat," often called the Caloris Basin, as seen by the MESSENGER probe.

Mercury: NASA / Johns Hopkins University Applied Physics Laboratory / Carnegie Institution of Washington | Moon: NASA / GSFC / ASU