What is the name of the largest impact basin on Mercury?

The largest impact basin on Mercury is the Caloris Basin. It spans about 1,550 kilometers and is one of the Solar System’s largest impact structures.

The basin formed roughly 3.8–3.9 billion years ago, when an asteroid-sized body struck Mercury during the era of heavy bombardment. The impact created a ring of mountains called the Caloris Montes, rising about 2 kilometers above the surrounding terrain. Lava later flooded much of the basin floor, producing the bright plain officially called Caloris Planitia.

“Caloris” comes from the Latin word for heat. The name reflects the basin’s unusual position: the Sun is nearly overhead there every second time Mercury reaches perihelion. Mariner 10 discovered the feature in 1974, but only part of it was visible; NASA’s MESSENGER spacecraft later photographed the entire basin. Caloris should not be confused with Mercury’s many smaller named craters.