NASA鈥檚 Viking 2 lander probably discovered quakes on Mars almost 50 years ago, but this has only just been confirmed thanks to data from the more recent InSight probe.
In 1975, NASA launched two missions to Mars, Viking 1 and 2, to study the planet鈥檚 surface and search for life. Both probes were also equipped with a seismometer to hunt for marsquakes, tremors on the Martian surface similar to earthquakes, to see if they existed.
Viking 1鈥檚 seismometer failed to operate, but Viking 2鈥檚 worked for two years. While rudimentary, the instrument did pick up at least two signals that were thought to be quakes, one of which had a magnitude of 3.5, while the other was of unknown strength. But mission scientists couldn鈥檛 be sure if they really were quakes or simply wind passing over the lander.
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鈥淲e couldn鈥檛 prove those two events,鈥� says , who is now retired but was a graduate student on the Viking team. 鈥淚t was very frustrating.鈥�
In 2018, another NASA lander called InSight was sent to Mars with a much more advanced seismometer 鈥� 鈥�200,000 times more sensitive than ours,鈥� says Lazarewicz. The lander picked up 1319 marsquakes, the largest being a magnitude-5 鈥溾��, proving their existence. It is thought marsquakes are mostly caused by the planet cooling and its crust cracking, or by meteorite impacts, as it is thought Mars today doesn鈥檛 have the tectonic plates that cause quakes on Earth.
Using these findings, Lazarewicz went back to the Viking 2 data. He found that the events seen by Viking 2 matched some of the quakes detected by InSight, with a similar signal that pointed to seismic activity and not just wind passing over the lander, all but confirming that Viking 2 did, in fact, detect the first marsquakes in the 1970s.
鈥淭he results are really fascinating,鈥� says at NASA鈥檚 Jet Propulsion Laboratory in California, the lead on InSight, which ran out of power in 2022. 鈥淚t was a little puzzling that [Viking 2] hadn鈥檛 seen anything.鈥�
There is still some uncertainty, however. 鈥淚t鈥檚 a very exciting, yet tentative, interpretation,鈥� says at Swiss Federal Institute of Technology Zurich in Switzerland. 鈥淭here are some more tests one could run that are necessary to put a high confidence in the result,鈥� he says, such as understanding the direction of the seismic waves recorded by the lander.
Aside from the historic interest, the findings could prove scientifically valuable. Viking 2鈥檚 landing site was relatively close to InSight, just 3000 kilometres away. They are both in a region called Utopia Planitia. The source of Viking 2鈥檚 marsquakes may have been Cerberus Fossae, a suspected site of former volcanic activity and the source of some of InSight鈥檚 marsquakes, potentially hinting at tectonic or remnant volcanic activity in this region.
鈥淚f Cerberus Fossae has been active since the 1970s, that is an interesting observation and tells us something about the source of the activity, whether it鈥檚 volcanic or tectonic,鈥� says Banerdt.
Viking 2鈥檚 results could help scientists narrow down the thickness of the Martian crust too, particularly at Utopia Planitia. 鈥淲e got 53 kilometres for the crustal thickness,鈥� says Lazarewicz, from InSight.
at the University of Oxford says the findings could also tell us something about the seasonality of marsquakes. 鈥淚鈥檒l be really interested to see whether the Viking data falls at the time of year we would expect an event at InSight鈥檚 location.鈥�
Lazarewicz hopes the reanalysis of Viking 2鈥檚 findings will bring some closure to the team. 鈥淲hen we ended with inconclusive results, everybody felt disappointed,鈥� he says. 鈥淭his is my way to repay the team. We did get marsquakes, and it was successful.鈥�
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