Decades ago, astronauts on the Apollo missions installed seismometers on the moon, which recorded thousands of lunar quakes until they were shut off in 1977.
Now the data collected by these instruments is getting a second life, as a new paper published in arXiv details. Physicists are using the old data to look for evidence of gravitational waves.
Sarah Zhang at Gizmodo explains what gravitational waves are:
What are gravitational waves and why do we care about finding them in the first place? Well, it goes back to a guy you may have heard of called Albert Einstein. Einstein's theory of general relativity says that gravity is caused by warps in the space-time continuum, and the warping also creates vibrations we call gravitational waves. These gravitational waves are tiny amounts of energy rippling through the universe.
Scientists haven’t been able to work out a way to directly observe gravitational waves, but are now using the data from the old seismometers to get an indirect glimpse of these vibrations as they passed through the moon. According to the arXiv blog, the researchers examined the data and looked for times when all of the seismometers registered activity at once. By looking for those kind of events, the researchers were able to establish a limit on a particular range of frequencies of gravitational waves. The new limit is more accurate than previous estimates, which were based on observations of the Earth.
Gravitational waves have been in the news lately with an announcement earlier this year that scientists had found evidence of gravitational waves (also through an indirect method of observation). However, later results indicate that the result may have just been caused by dust.