Seismic evidence for a low‐velocity lunar core

The seismic evidence for a low‐velocity lunar core has been reexamined. A relocation for a meteorite impact on day 263 in 1973, which was the event used to first estimate the size of the lunar core, has been found which can explain the arrival time and signal amplitude data without requiring the presence of a lunar core. However, tentative identification has been made of arrivals in the seismograms of two of the largest, most distant impacts detected by the lunar seismic network during its period of operation which may have travelled through a lunar core about 400 to 450 km in radius, and with a P wave velocity of about 5 km/s. Thus the lunar seismic data remain ambiguous but can be interpreted in terms of there once being a small liquid core, as required by palaeomagnetic observations.