Fifty Years Later: Revisiting Viking 2 Seismic Signals Through InSight

Abstract

For nearly 50 years, the origin of the candidate seismic signals recorded by Viking 2 remained unresolved because of limited instrumental sensitivity, onboard observation, data compression, and the absence of Martian seismic context. Here we reconstruct the Viking seismic workflow and reinterpret the two Viking candidate events, recorded on sol 53 and sol 80, using the seismic context established by InSight. We show that the Viking seismometer was optimized for high‐spectral‐frequency seismic signals, consequently reducing its sensitivity to low‐spectral‐frequency events. If the original 10‐s S‐P travel‐time difference is correct, the inferred location of the sol 80 event overlaps the broad northern‐plains source region suggested for the seasonally recurrent high‐spectral‐frequency and 2.4‐Hz marsquake populations observed by InSight. Alternatively, if the first‐arrival phase represents a crustal conversion phase rather than a direct P wave, the sol 80 event corresponds to a distant tectonic (low‐spectral‐frequency or broadband) marsquake with an estimated moment magnitude of M _W 4.6–4.8 or M _W 4.9–5.1. A meteorite impact origin cannot be excluded either. The two Viking seismic signals decay more rapidly than typical InSight marsquakes, suggesting heterogeneity in the Martian attenuation structure. Together, these findings integrate Viking observations into the modern framework of Martian seismicity, illustrating how a legacy planetary data set can acquire renewed scientific implications when re‐examined in light of subsequent mission data.