The Moon’s fluid core was identified indirectly by Lunar-laser ranging (LLR) data in the 1980s and subsequently confirmed by magnetic and seismic data analyses from the Apollo mission. Estimates of the size of the fluid core did vary by +/- 55 km, however.
A team from the Paris Observatory and Observatory of the Côte d’Azur (OCA) has now managed to determine a Moon core size of 381 km with an accuracy of +/- 12 km, which is three times better than previous individual estimates. The researchers, who report their work in Geophysical Research Letters, obtained their result using Laser-Moon telemetry data from LLR.
Read the research paper: Observational Constraint on the Radius and Oblateness of the Lunar Core‐Mantle Boundary. V. Viswanathan et al. Geophysical Research Letters 10.1029/2019GL082677