• Seismic event on the Moon. Seismic detectors left on the Moon by Apollo astronauts show that there are few Moonquakes – a few thousand per year compared to up to ten times as many for the Earth. They tend to occur deep down, up to 800km below the lunar surface, and cluster in a monthly cycle, suggesting a link to frictional and tidal forces set up by the Moon’s orbital motion around the Earth.