some missions, the astronauts brought back soil and rock samples from the Moon. Once
back at Earth, the samples were studied to help scientists learn about the surface features of
the Moon. No astronauts have visited the Moon since 1972, but in 2004 the United States
President George W. Bush called for a return to Moon exploration by the year 2020. Maybe
you can be one of the astronauts to return to the Moon!
This lesson focuses on how the Moon was formed and gives a description of the features
and characteristics of the Moon—many of which were investigated and discovered during
the major years of lunar exploration in the 1960s and 1970s.
Figure 24.12: Astronaut Buzz Aldrin walks on the Moon on July 20, 1969. ( 17 )How the Moon Formed
Astronomers have carried out computer simulations showing that the collision of a Mars-
sized object with the Earth could have resulted in the formation of the Moon. Additional
data shows that the surface of the Moon dates to about 4.5 billion years ago, suggesting
that the collision occurred during the heavy bombardment period, about 70 million years
after the Earth formed. The Moon also has a relatively small core and appears to be largely
comprised of the same basalt material found in the Earth mantle. Such a collision would