The Caloris Basin, also called Caloris Planitia, is an impact crater, on Mercury, which is ~1350km in diameter. Caloris is Latin for heat and the basin is so-named because it is near the subsolar point when Mercury is at perihelion. The crater is surrounded by a ring of mountains, ~2km in height.

Caloris was likely created by the impact of an object 100+km in diameter; this impact is believed to have penetrated the crust. It is generally believed that energy from the impact was focused, as with a lens, such that it traveled through the planet and created ~500,000km² of disrupted terrain on the opposite side. This area is covered with hills, some of which are 1800m in height.

See also:

• Mare Orientale (on the Moon)