Seismology has long been one of the best ways to probe a planet's interior, but early attempts to use it on Mars were inconclusive. Viking 2 recorded just two ambiguous events, while Viking 1's seismometer never deployed correctly. Now, researchers have compared those old measurements with data from NASA's InSight lander, which operated on Mars from 2018 to 2022.
The new analysis, by Xiao et al. in AGU Advances, finds that one Viking 2 event could indeed have been a real marsquake. It may have originated from the same region where InSight later recorded a swarm of nearly 1,000 marsquakes, suggesting that this area has remained seismically active for almost half a century.
Still, the identification is not certain. Viking 2's seismometer was mounted on the lander deck, so it was sensitive to wind noise, and either of the two reported events could have been a false signal. InSight's seismometer, by contrast, sat directly on the ground and detected more than 1,300 seismic events. The new study strengthens the case that at least one of Viking's ambiguous readings was a genuine marsquake, but the evidence remains suggestive rather than definitive.