Planetary scientists still debate the moons
formation, with three primary theories dominant in the past....
(i) The moon formed in some other part of
the solar system and was gravitationally snared by the earth – this
is what is known as the 'Capture Theory.'
(ii) The moon was once part of the earth,
but calved from it early in their history – this is what is known
as the Fission Theory.
(iii) The earth and moon formed together
but independently, as many of the moons in the solar system formed
– the 'Sister Theory.'
Each of these theories have their problems,
for example the gravitational models argue strongly against earth
being able to capture a satellite as large as the moon, and a fourth
theory is now favoured by most astronomers. According to the Giant
Impact Theory a glancing, high speed collision between the primitive
earth and a Mars size body smashed earths crust and melted rock
deep within the mantle. Molten rock from both the earth and the
impacting body was jetissoned into space, condensing into a ring
of orbiting debris. This material then coalesced, cooled and solidified
into what we know to be the moon.
When looking at the moon through a telescope
one can see a surface covered with craters. Many of these formed
during the first 800 million years of the moons history during a
period of intense bombardment that pulverised and abraded the young
moon's crust. The pummeling resulted in the huge impacts that created
the larger lunar basins and craters. The naked eye can easily discern
the Moons mottled surface of bright and dark patches. The bright
regions consist of mountain ranges, uplands, material ejected when
craters were formed, and regolith, the moons fine grained soil.
Dense concentrations of craters occur in these areas, ranging in
size from tiny pits to huge bowls with central mountain peaks and
walled plains. The dark regions are lightly cratered basins and lowlands
called Maria, which were formed by floods of lava early in the moons
history. Today the moon is a quiet place, impacts being rare and
volcanic activity at least a billion years in the past. Seismic
activity is very low, and so the moon is now all but geologically
The moon is made up of largely different
materials to those predominating on earth. Density is an important
clue to interior composition, and planetary scientists cite the
moons low density as evidence that it must be composed almost entirely
of light silicate rocks. Unlike earth, the moon is deficient in
iron and metals, and nearly devoid of materials that are gaseous
at low temperatures. Modest reserves of water ice however were detected
by the Lunar prospector mission in the late 1990s. Prospectors data
indicated that as much as six billion tons of ice lies buried 18
inches below ground in the permanently shadowed craters at the poles.
There is enough water to support a city of 360,000people for well
over a century without recycling.
This satellite lacks a significant metal
core and a global magnetic field, though evidence suggests that
a much stronger field once existed. Researchers theorize that it
dwindled because the moons initial core was never large or hot enough
to produce the kind of powerful convection currents needed to create
a strong field