What Are Lunar Seas (Maria)?

Lunar maria (singular: mare) are the dark, smooth plains on the Moon’s near side—Latin for "seas," though they contain no water.

Origin

They are vast basaltic lava flows from ancient volcanic eruptions 3–4 billion years ago, flooding giant impact basins. The basalt’s iron-rich composition makes them darker than the surrounding highlands.

Key Facts

• Cover ~16% of the lunar surface (mostly near side).
• Largest: Mare Imbrium (1,145 km diameter).
• Concentrated on the near side due to thinner crust from Earth’s tidal influence.
• Apollo 11, 12, 14, 15, 16, 17 all landed in or near maria.

Maria are windows into the Moon’s volcanic past and the early solar system’s violent history.