“The moon 's an arrant thief, And her pale fire she snatches from the sun.” William Shakespeare THE MOON

The Moon has large dark flat areas, due to lava flow, called Maria. (early observers thought they were oceans) THE SURFACE OF THE MOON

Highlands – light colored areas that resemble Earth’s continents Elevated several kilometers above the Maria

The far side of the Moon is relatively unmarked. THE SURFACE OF THE MOON

Crater formation: Meteoroid strikes the Moon, ejecting material; explosion ejects more material, leaving a crater. THE SURFACE OF THE MOON

Craters are typically about 10 times as wide as the meteoroid creating them, and twice as deep. Rock is pulverized to a much greater depth. Most lunar craters date to at least 3.9 billion years ago; much less bombardment since then. THE SURFACE OF THE MOON

Very large and very small lunar craters THE SURFACE OF THE MOON

Regolith: Thick layer of dust left by meteorite impacts The Moon is still being bombarded, especially by very small “micrometeoroids”; softens features.

ATMOSPHERE There is no atmosphere on the moon Escape speed is only 2.4 km/s Earth’s is 11.2 km/s

INTERIOR Iron-poor compared to Earth Still has an iron core Uniform density but chemically differentiated Has layers like the earth

HISTORY OF THE EARTH–MOON SYSTEM Four billion years ago, the Moon had many craters but no maria. By three billion years ago, the maria had formed. Now, they also are covered with craters.

Current theory of the Moon’s origin: glancing impact of Mars-sized body on the still-liquid Earth caused enough material, mostly from the mantle, to be ejected to form the Moon. Computer model HISTORY OF THE EARTH–MOON SYSTEM