The first observations of tectonics on another planet have been taken since February 2019 by NASA’s Interior Exploration utilising Seismic Investigations, Geodesy and Heat Transport (InSight) lander. Seismologists and geophysicists at ETH Zurich created the Seismic Experiment for Interior Structure (SEIS) instrument for InSight, which has been on the surface watching for signs of “marsquakes.” What planetary scientists have long suspected—that Mars is generally quiet—has been largely validated by the dataset it has obtained (more than 1,300 seismic occurrences).
However, a recent analysis of a cluster of more than 20 recent marsquakes by a study team led by ETH Zurich showed something quite intriguing. They came to the conclusion that the majority of Mars’ widely dispersed surface faults are not seismically active based on the location and spectral characteristics of these events. However, the majority of the 20 recorded seismic occurrences were located close to the rift-filled Cerberus Fossae (or graben). These findings imply that volcanism and geological activity continue to actively shape the Martian surface.
Simon C. Stähler, a senior scientist in the Seismology and Geodynamics group at the Institute for Geophysics at ETH Zurich, served as the study’s principal investigator. Researchers from Harvard University, the Laboratory of Planetology and Geodynamics (LPG) at the Université Paris Cité, the German Aerospace Center’s Institute of Planetary Research (IPR), and NASA’s Jet Propulsion Laboratory joined him and his colleagues. Recently, the journal Nature Astronomy published a study titled “Tectonics of Cerberus Fossae exposed by marsquakes” that details their discoveries.
The scientists came to the conclusion that low-frequency quakes might be a sign that molten magma is now present in the Martian mantle based on the seismic data collected by InSight. In particular, they discovered that the epicentres of these quakes were primarily found in the deepest region of Cerberus Fossae, at depths of 30 to 50 km (18.6 to 31 mi). The topography is sinking beneath its own weight in this region, which has the name of the hellhound that guards the entrances to Hades (the underworld in Greek mythology), pulling the crust of Mars apart.
The scientists hypothesised that either magma is flowing eastward beneath the surface in preparation for its next eruption or that these tremors could be the last from this formerly active volcanic region. The scientists found that these earthquakes occurred quite close to a feature in the Cerberus Fossae Mantling Unit, which was previously referred to as a “young volcanic fissure,” when they looked at orbital pictures of this region. Dark dust deposits were prevalent all around this feature, not just in the direction where the wind was blowing the most strongly (as was expected).
The only explanation for this, according to Stähler, was the presence of recent volcanic activity, as stated in a recent ETH Zurich press release. According to him, the older age of the dust indicates relatively recent volcanic activity, perhaps within the last 50,000 years.
Mars offers possibilities to study geological processes that are similar to those that shaped our planet because of its terrestrial (rocky) makeup and proximity to Earth. Venus is closer than Earth, but its extremely dense atmosphere makes it impossible to examine it with anything else than surface-mapping radar and temperatures hot enough to melt lead. The only other bodies in the Solar System that have been investigated are orbiters and probes due to their separation from Earth, which causes communication delays.
Mars is also the only other terrestrial planet known to have an iron, nickel, and sulphur core, which may have once supported a magnetic field. This field is created on Earth by the dynamo action of a liquid outer core rotating around a solid inner core (contrarily to the direction of Earth’s rotation). The Red Planet’s interior is thought to have rapidly cooled some 4 billion years ago, causing the outer core to harden while the inner core melted. Without this field, the solar wind would have progressively eroded Mars’ atmosphere over ages.
This was formerly thought to also imply that Mars had a geological death billions of years ago. However, these and other cues from robotic missions imply that geological activity hasn’t completely stopped on the Red Planet. The possibility of magma in Mars’ mantle today is intriguing, even though there is still much work to be done to corroborate these findings. These findings show the potency of the InSight lander and its sophisticated equipment as well as the synergistic effects of other robotic missions. Domenico Giardini, a co-author, said:
The most sensitive seismometer ever put on another planet is InSight’s SEIS. It gives geophysicists and seismologists a chance to work with up-to-date information about what is occurring on Mars right now, both at the surface and inside.
Many more robotic rovers, landers, and orbiters will be heading to Mars in the upcoming years. Their investigation of the geology, ecology, climate, and atmosphere of Mars’ surface will prepare the way for crewed missions slated for the 2030s.