Asked by: Richard Ward, Lutterworth
No observations or theoretical claims for additional moons of the Earth have ever been substantiated. However, some astronomers have speculated that there may have been a companion moon very early in Earth’s history. An impact with this ‘other’ moon may help explain how the Moon’s nearside is low and flat and is dominated by volcanic maria (or ‘seas’), whereas the far side is mountainous and deeply cratered. It can also explain the distribution of certain chemical elements on the Moon. However, other processes can also account for these observations, so the ‘other moon’ idea is still hypothetical.
The Earth does, however, have some very small satellites that could be classed as moons. In 2006 a tiny asteroid, 2006 RH120, was discovered in Earth’s orbit. This ‘captured’ object remained in Earth orbit for 13 months before returning to a solar orbit. These ‘temporary’ moons are thought to be quite common.