NASA’s InSight Mars lander has detected many small marsquakes, mostly from a region called Cerberus Fossae. Analysis of 47 quakes suggests their origin is volcanic, not tectonic. If so, it means the era of Martian volcano building may not be over – although we probably shouldn't expect to witness great eruptions filling the red planet's skies with ash.
Earth experiences two sorts of quakes, excluding those induced by human activity. Tectonic earthquakes occur when plates slide past or under each other. Volcanic earthquakes are a consequence of rapid movements of magma or a buildup of gas pressure in the crust. Some other worlds have neither sort, their surface only shaking from external events such as a meteor strike, but what about Mars?
In the journal Nature Communications The Australian National University’s Professor Hrvoje Tkalčić and Dr Weijia Sun of the Chinese Academy of Sciences have challenged the expectation that quakes detected by Insight’s seismometers are tectonic in origin, implying Mars still has mobile magma in its mantle. That tongue-twister could make the red planet's geology more interesting, and tell us where we should focus future geological attention.
It's no secret that Mars was once volcanic; the evidence is there in the Solar System’s largest volcano, Olympus Mons. At 21.9 kilometers (13.6 miles) high, it's over double Everest's altitude. Other enormous volcanoes are nearby in the Tharsis Montes volcanic region. However, Olympus Mons formed over three billion years ago, and is not thought to have erupted for hundreds of millions of years. Other known Martian volcanoes are even older.
This has led some planetary scientists to suspect we have missed the chance to witness a Martian volcano in formation, but Tkalčić is not so sure.
"InSight has detected high and low frequency quakes” Tkalčić told IFLScience. “Our paper only looked at low frequency quakes. We detected that some of these are repetitive in a way that cannot be explained for tectonic quakes.”
Tkalčić and Sun looked for comparable examples on Earth, and found similar wave patterns in quakes produced by dormant volcanoes. This, they concluded, makes it highly probable that these quakes are volcanic.
That doesn't mean we can expect to see lava and ash bursting forth from some new Martian peak. Tkalčić explained to IFLScience; “Martian volcanism is intrusive volcanism, magma doesn't find a way to the surface.” The reasons for this include the thickness of the Martian crust compared to the planet's size, and perhaps the chemical properties and temperature of the magma. A new uplifting might excite planetary scientists, even if others might wish for the spectacle of eruptions.
Tkalčić told IFLScience the Cerberus Fossae quakes were previously thought to be tectonic because the fissures and steep faults that give the area its name indicate the presence of tectonic activity in the relatively recent past. Over 1,000 kilometers away from the Tharis Montes province, there was no reason to suspect this was another location of rising magma.
The quakes are small, none reaching magnitude 4 – but Tkalčić told IFLScience this may not always be the case, with marks on Mars indicative of relatively recent magnitude-7 activity, the sort that destroys cities on Earth.
Previous efforts to use InSight to identify quakes had struggled to distinguish movements from noise caused by the Martian wind, usually only succeeding in the dead of night when the wind drops.
By using more advanced processing methods to separate signal from noise; "We found that these marsquakes repeatedly occurred at all times of the Martian day,” Tkalčić said in a statement. This ruled out the possibility that what was being detected previously was caused by adjustments to the large change in temperature between day and night.