Magnetic Field (Earth = 10) - 0,

The surface of the Moon can be divided into two major regions: (a) the relatively low, smooth, dark areas called maria (seas, 16% of the Moon's surface) which are vast plains of basaltic lava and (b) the densely cratered, rugged highlands, originally called terrae (land). Craters on the Moon are the result of impacts.

Major lunar rock types include: (a) anorthosite, (b) basalt, (c) breccia, and (d) glass.

The Moon is a differentiated planetary body with a crust about 70 km thick. The lithosphere is approximately 1000 km thick. The deeper interior may consist of a partially molten asthenosphere and a small metallic core. The tectonic and thermal evolution of the Moon was very rapid and terminated more than two billion years ago. The major events in the Moon's history were: (a) accretion and differentiation with the formation of the lunar crust by crystallization of a magma ocean, (b) intense meteoritic bombardment, (c) extrusion of the mare lavas, and (d) light bombardment.

Beneath the lunar crust (about 65-150km thick and thinner on the Earth-facing side. NOTE: the same side always faces us) is the lunar mantle, which is the largest part of the Moon. There might be a difference in rock types above and below a depth of 500 km, related to the depth of the lunar magma ocean. Beneath the mantle lies a small lunar core made of metallic iron. The size of the core is highly uncertain, with estimates ranging from about 100 km to 400 km.

The Moon does not have much of a magnetic field, so the lunar core is not generating magnetism. However, Lunar rocks are magnetized with older rocks have stronger magnetism, suggesting that the Moon's magnetic field was existent and stronger in the past.

The highlands are largely composed of anorthosite, a rock enriched in plagioclase which accumulated by flotation of the relatively light plagioclase minerals in a magma (molten rock). 4.5 billion years ago the Moon was covered by a layer of magma (about 500Km thick), the lunar magma ocean.

These igneous rocks were melted, broken up and mixed by impacts during the Moon’s first half billion years. These rocks are called breccias. Most dated breccias fall into a narrow span of ages (3.85 to 4.0 billion years), indicating that the Moon was subjected intense bombardment during that narrow time interval.

From 3.8 to 3.2 billion (the lower limit may be as low as 2.5 billion) years ago lunar basalts extruded, forming the mare. The melting took place at depths ranging from 100 to 500 km, and the rocks that partially melted contained mostly olivine and pyroxene. The mare basalts may only be about 1 km thick, representing a thin veneer on this mostly plagioclase-rich crust.

From about 3.2 billion years ago until today the moon has only experienced light bombardment by meteorites. The Moon is not presently geologically active. (There are weak moonquakes which occur periodically at depths of 800-1000km depth, deeper than the deepest earthquakes)

The origin of the Moon is best explained by the impact theory, according to which the Earth collided with a Mars sized object and that the Moon formed from the ejected material. More than a trillion trillion tons of material vaporized and melted. In some places in the cloud around the Earth, temperatures exceeded 10,000°C. The impact also increased the rotation of the Earth. This theory explains the "low" density of the moon, the lack of volatiles in lunar rocks and the size of the Earth core.

The Earth has a large iron core, but the moon does not. This is because Earth's iron had already drained into the core by the time the giant impact happened. Therefore, the debris blown out of both Earth and the impactor came from their iron-depleted, rocky mantles. The iron core of the impactor melted on impact and merged with the iron core of Earth, according to computer models.

Earth has a mean density of 5.5 grams/cubic centimeter, but the moon has a density of only 3.3 g/cc. The reason is the same, that the moon lacks iron.

The moon has exactly the same oxygen isotope composition as the Earth, whereas Mars rocks and meteorites from other parts of the solar system have different oxygen isotope compositions. This shows that the moon formed form material formed in Earth's neighborhood.

 Ice on the Moon

On 5 March 1998 it was announced that data returned by the Lunar Prospector spacecraft indicated that water ice is present at both the north and south lunar poles, in agreement with Clementine results for the south pole reported in November 1996. The ice originally appeared to be mixed in with the lunar regolith (surface rocks, soil, and dust) at low concentrations conservatively estimated at 0.3 to 1 percent. Subsequent data from Lunar Prospector taken over a longer period has indicated the possible presence of discrete, confined, near-pure water ice deposits buried beneath as much as 18 inches (40 centimeters) of dry regolith, with the water signature being stronger at the Moon's north pole than at the south (1). The ice was thought to be spread over 10,000 to 50,000 square km (3,600 to 18,000 square miles) of area near the north pole and 5,000 to 20,000 square km (1,800 to 7,200 square miles) around the south pole, but the latest results show the water may be more concentrated in localized areas (roughly 1850 square km, or 650 square miles, at each pole) rather than being spread out over these large regions. The estimated total volume of ice is 6 trillion kg (6.6 billion tons). Uncertainties in the models mean this estimate could be off considerably.

The Earth's rotation carries the Earth's bulges slightly ahead of the point directly beneath the Moon. This means that the force between the Earth and the Moon is not exactly along the line between their centers producing a torque on the Earth and an accelerating force on the Moon. This causes a net transfer of rotational energy from the Earth to the Moon, slowing down the Earth's rotation by about 1.5 milliseconds/century and raising the Moon into a higher orbit by about 3.8 centimeters per year. Note: this is the opposite of what is happening to Tritan.