The Moon is the only satellite of Earth and is the fifth-largest satellite in the Solar System. It is responsible for the tidal forces on Earth.
Mass: 7.35 x 1022 kg
Composition: Iron and minerals
Orbit: 384,400 km from Earth
It is widely thought that the Moon was created as a result of a large impact with Earth. The material that broke off is believed to have formed the Moon and become a satellite of Earth. The Moon is very dense, second only in its density to Io, one of the Galilean Satellites of Jupiter.
Earth’s moon is known simply as ‘The Moon’. Until Galileo’s discovery of Jupiter’s moons, it was not known that any other moons existed. A moon is the term now used to describe satellites which orbit a body in the Solar System, but they are now given unique names.
The Moon has a solid iron inner core which is surrounded by a liquid iron outer core. The mantle is composed of various minerals and the Moon’s crust was formed by parts of a molten layer floating to the surface. This crust is 50 km deep. A lack of gravity on the Moon means that it regularly gets hit by objects which collide with the surface. This has led to the surface being covered in dust and rocky deposits. Despite this, the Moon is the brightest body in the Solar System excluding the Sun.
The surface of the Moon has been studied extensively and its geographical features mapped out. South Pole-Aitken is the largest crater present on the Moon, measuring 2,240 km wide and 13 km deep. Other significant craters are Imbrium, Serenitatis, Crisium, Smythii and Orientale.
The Moon orbits Earth in 27.3 days and is in synchronous rotation with it. The same side of the Moon is always seen from Earth, as it rotates on its axis in the time that it takes to travel all the way around Earth. The side which is visible from Earth is referred to as the near side and the opposite side is the far side. In contrast with other satellites, the Moon’s orbit is nearer the ecliptic plane than to the planet’s equatorial plane.
In 1959, the first space missions to the Moon were made by the unmanned Russian spacecraft Luna 1 and Luna 2. The US followed this with exploratory visits made by robotic equipment to prepare for a manned mission which would eventually land on the Moon. This became reality on 20th July 1969, when Apollo 11 safely landed on it. This was followed by the momentous occasion when Neil Armstrong became the first person ever to step onto the Moon. The Apollo missions collected samples from the surface of the Moon and brought them back to Earth for analysis.