Craters of the Moon

Read Ch. 4 of the text, sections 4.1 through 4.6

William Herschel thought he saw 3 volcanos on the moon in 1787

Arguments circa 1920 in favor of a volcanic origin

• Few impact craters known on Earth– Meteor crater

(Barringer crater) in Arizona

Moon craters are mainly round

• If impacts came in from all directions, wouldn’t we have more elongated craters?

Small craters overlap large craters, rather than vice versa

Some thought they saw craters in the central mountain peaks

Impact origin

• Championed by G.K. Gilbert and others in the 19th century, but didn’t really take hold until the middle of the 20th

A Michigan native, Ralph Baldwin, helped turn the argument in favor of impacts

Baldwin compared craters produced by explosions on the earth with the craters of the moon

• He found that they followed the same trend of diameter versus depth

• Impacts produce a generally round explosive crater regardless of direction of impact

Apollo Landings

• Lunar rocks mainly breccias – rocks shattered by impacts

Crater Types

Simple craters are relatively small

Complex craters are bigger

Copernicus

If Copernicus were 9-inches across, its depth would be only 1/3 of an inch!

King Crater

Basins: the Largest impact features

Orientale basin

Mare Imbrium

Mare Imbrium

Mare Humorum