Sea of Rains

A round plain left by a giant impact

The Sea of Rains is the big round dark patch at the upper left of the Moon. A giant asteroid made it 3.9 billion years ago, and later lava filled the hollow. A ring of mountains surrounds it: the Alps, Apennines and Caucasus — named after Earth's mountains! In 1971 the Apollo 15 astronauts drove a Moon car here.

The Sea of Rains (Mare Imbrium) is the Moon's second-largest impact basin, 1,145 km across, formed ~3.9 billion years ago by a 250 km body. Ring mountains surround it: the lunar Apennines (up to 5 km), Alps and Caucasus. Inside are the craters Archimedes and Aristillus; Plato sits on its rim. Apollo 15 (1971) landed at Hadley–Apennine and used the first lunar rover; China's Chang'e 3 (2013) also landed in this sea. The Imbrium impact marks a boundary in the Moon's geological timescale.

Fun facts

• The Sea of Rains could hold Uzbekistan twice over.
• The lunar Apennines are taller than Earth's Apennines — 5 km!
• The Apollo 15 rover drove 28 km on the Moon — from one side of a city to the other.