Asked by: John Morris, by email
This was one of the questions the Apollo missions were tasked with resolving over 40 years ago, but only now is the answer becoming clear. The astronauts placed seismometers on the lunar surface to detect ‘moonquakes’, in the hope that analysis of how the shockwaves travelled through the Moon would reveal what lay at its core. The seismometers were finally switched off in 1977, and scientists have been trying to make sense of the data ever since.
One major problem has been finding the signals of deep moonquakes among the ‘noise’ of other events, including meteor impacts. Using computers to clean up the data, a team led by Dr Renee Weber of NASA’s Marshall Space Flight Center in Huntsville, Alabama, has now found evidence that the Moon has a core very similar to that of the Earth, with a solid innermost region, and a molten outer core.