Back in the 1960s, physicist Joseph Weber tried to catch gravitational waves using aluminum cylinders: they were supposed to tremble like tuning forks from the ripples of spacetime. Modern detectors like LIGO, built with the involvement of Rainer Weiss, register such vibrations from black hole mergers. But what if we turned the whole Moon into an antenna? When a wave passes through the satellite, it starts ringing like a bell. By analyzing the frequencies and amplitude of this ringing, much like spectroscopy uses the color of light to determine the composition of stars, geophysicists reconstruct the internal structure: where the dense rocks are and where, perhaps, a molten core hides. The precision of this 'eavesdropping' increases tenfold compared to conventional seismology. And to make the Moon ring, no explosions are needed, just cosmic cataclysms billions of light-years away.
Lunar rocks lack moisture, which on Earth quickly dampens vibrations, so moonquakes last from ten minutes to several hours, an ideal environment for 'eavesdropping' on faint gravitational-wave signals.