A peer-reviewed study published September 30, 2026, calls Viking 2’s Sol 80 recording its clearest seismic candidate, rather than a confirmed marsquake. The paper also considers a meteorite impact as a possible source. Read the study in AGU Advances.
NASA’s Viking 2 lander recorded two unusual signals in 1976, on Sol 53 and Sol 80. The later Sol 80 signal is the stronger candidate in the 2026 analysis, but its source depends on how researchers interpret the first arrival in the record.
How researchers reexamined Viking’s records
Viking’s seismometer sat on the lander, and its event-mode system transmitted compressed measurements of signal amplitude and zero crossings at about 1 Hz, rather than conventional full waveforms. The instrument was most sensitive around 3 Hz and less sensitive to lower-frequency signals.
The 2026 study reconstructed Viking’s recording workflow, then simulated how seismic observations from InSight would look if processed in Viking’s format. That let the researchers compare the older records with later Mars observations while accounting for the differences between the two systems.
The Sol 80 signal peaked at about 30 digital units; the estimated nighttime background was about 10. Its nearest wind reading was about 2.6 m/s, measured 20 minutes before the signal. The timing and amplitude help characterize the record, but the wind measurement was not simultaneous with it.
Why Sol 80 has several possible explanations
The interpretation turns partly on the signal’s first arrival. If it was a direct P wave, the source may lie in the broad northern-plains region associated with seasonal marsquakes observed by InSight. If it was a crustal-conversion phase, the signal could instead point to a distant tectonic marsquake. A meteorite impact is another possible explanation.
For the distant-tectonic interpretation, the paper gives conditional moment-magnitude estimates of Mw 4.6–4.8 using the near-vertical X component, or Mw 4.9–5.1 using the Z component. Those estimates depend on the interpretation and signal component; they are not established magnitudes for a confirmed quake.
What an earlier study concluded
A 2023 paper concluded that both Viking 2 signals, Sol 53 and Sol 80, were marsquakes. The 2026 analysis describes the records as candidates and identifies Sol 80 as the clearer case. The papers therefore reach different strengths of conclusion, while the later analysis leaves the signal’s source open. Read the 2023 paper.
