Time before present (billion years)Rate of Crater FormationCratering rate relative to present106105104103102101
4 321NowNASANASANASA
Mare OrientaleLunar rover Sun glare in
camera lensSolidified lavaIn larger craters, the
deformation of the
rock can form one or more
inner rings concentric with the
outer rim. The largest of these
craters are called multiringed
basins.In Mare Orientale on
the west edge of the visible moon,
the outermost ring is almost 900 km
(550 mi) in diameter.Visual-wavelength imagesVisual-wavelength imagesMeteorite from moon
The age of the moon rocks provide
evidence of a late heavy
bombardment 4.1 to 3.8 billion
years ago.Cratering events in the inner solar
system are now roughly a million
times less common than they were
when the solar system was young.Late
Heavy
Bombardment2a2 Plum Crater (right), 40 m (130 ft) in diameter, was
visited by Apollo 16 astronauts. Note the many
smaller craters visible. Lunar craters range from giant
impact basins to tiny pits in rocks struck by
micrometeorites, meteorites of microscopic size.Plum Crater (right), 40 m (130 ft) in diameter, was
visited by Apollo 16 astronauts. Note the many
smaller craters visible. Lunar craters range from giant
impact basins to tiny pits in rocks struck by
micrometeorites, meteorites of microscopic size.3 Most of the craters on the moon were
produced long ago when the solar system
was filled with debris from planet building. As
that debris was swept up, the cratering rate fell
rapidly, as shown schematically below.Most of the craters on the moon were
produced long ago when the solar system
was filled with debris from planet building. As
that debris was swept up, the cratering rate fell
rapidly, as shown schematically below.2b The energy of an impact can melt
rock, some of which falls back into
the crater and solidifies. When the moon
was young, craters could also be flooded
by lava welling up from below the crust.A few meteorites found on Earth have
been identified chemically as fragments
of the moon’s surface blasted into space
by cratering impacts. The fragmented
nature of these meteorites indicates that
the moon’s surface has been battered by
impact craters.The energy of an impact can melt
rock, some of which falls back into
the crater and solidifies. When the moon
was young, craters could also be flooded
by lava welling up from below the crust.A few meteorites found on Earth have
been identified chemically as fragments
of the moon’s surface blasted into space
by cratering impacts. The fragmented
nature of these meteorites indicates that
the moon’s surface has been battered by
impact craters.