have been incredibly powerful, producing oceans of liquid magma over much of the surface
of the Earth.
The explosive impact that likely led to the formation of the Moon would have produced a
huge amount of energy, leaving the surface of the Moon in an initiallymoltenstate. This
means that its surface would have been hot and fluid, like magma inside the Earth today.
The magma eventually cooled and hardened so that the Moon now has a solid surface.
Lunar Characteristics
The Moon is Earth’s only natural satellite. Asatelliteis a body that moves around a larger
body in space. The Moon orbits Earth in the same way that the Earth orbits the Sun, and
the Moon remains close to Earth because of the strength of Earth’s gravity. The Moon is
3,476 kilometers in diameter, about one-fourth the size of Earth. Because the Moon is not
as dense as the Earth, gravity on the Moon is only one-sixth as strong as it is on Earth. You
could jump six times as high on the Moon as you can on Earth.
If you watch the Earth and the Moon from space, the Moon makes one complete orbit around
the Earth every 27.3 days. The Moon also rotates on its axis once every 27.3 days. Thus, the
same side of the Moon always faces Earth. This means from Earth we always see the same
side of the Moon. The side of the Moon that faces Earth is called the near side (Figure
24.13). The side of the Moon that faces away from Earth is called the far side (Figure
24.14). The Moon makes no light of its own, but instead only reflects light from the Sun.
The Lunar Surface
The Moon has no atmosphere. The average surface temperature during the day is approxi-
mately225°Fandcanreachtemperaturesashighas253°F.Atnighttheaveragetemperature
drops to -243°F and has been measured as low as -397°F. These extremely cold temperatures
occur in craters in the permanently shaded south polar basin and are amongst the coldest
temperatures recorded in our entire solar system.
There are no lakes, rivers, or even small puddles anywhere to be found on the Moon’s surface.
(However, it should be noted that in 2009, NASA scientists believe they discovered that in
the top few millimeters of the Moon’s surface, there is a large number of water molecules
mixed in with dirt and rocks — you can stay up-to-date with their latest findings athttp:
//www.nasa.gov). Yet, despite the possible presence of water, with a lack of atmosphere
and extreme temperatures, it comes as no surprise to scientists that there has been zero
evidence of life naturally occurring on the Moon.
Although there are no ”naturally occurring” signs of life on the Moon, there are signs that
life has encountered the Moon — that is, there are footprints of astronauts on the Moon’s
surface. It’slikelythatthesefootprintswillremainunchangedforthousandsofyears,because