lunar rock samples or the lunar Love numbers. The Weber et al. paper provides the first direct evidence of seismic wave reflections off the lunar core.
This finding is a big deal because by knowing the structure of the lunar core, we can understand the moon's present and past thermal state, the history of the lunar dynamo, and the origin and evolution of the Moon. After all, the prevailing theory is that the Moon formed from a giant impact into the Earth, so its history tells us a great deal about our own planet too.