Mare Imbrium is a lava plain within the Imbrium Basin on The Moon and is one of the larger craters in the Solar System. The Imbrium Basin formed from the collision of a protoplanet during the Late Heavy Bombardment. Basaltic lava later flooded the crater to form the flat volcanic plain seen today. The basin's age has been estimated using uranium–lead dating methods to around 3.922 billion years ago, and the diameter of the impactor has been estimated to be around 250 ± 25 km. Mare Imbrium was the location of the first robotic rover deployed on an extraterrestrial body.