Mare Imbrium (
Latin for "
Sea of Showers" or "
Sea of Rains") is a vast
lunar mare filling a basin on the
Moon. One of the
larger craters in the Solar System, Mare Imbrium formed when
lava flooded the giant
crater formed when a very large object hit the Moon long ago. Its age has been estimated using U-Pb dating methods to 3938 ± 4 Ma. The Moon's maria (plural of
mare) have fewer features than other areas of the Moon because molten lava pooled in the craters and formed a relatively smooth surface. Mare Imbrium is not as flat as it was originally because later events have altered its surface.