June 5, 2023
Mars is mostly dead.  There's still magma in there, so it's slightly alive

Mars is mostly dead. There’s still magma in there, so it’s slightly alive

As of February 2019, NASA’s Inland Exploration using Seismic Surveys, Geodesy and Heat Transfer (InSight) lander is making the first measurements of tectonics on another planet. Key to this is InSight’s Seismic Experiment for Interior Structure (SEIS) instrument (developed by seismologists and geophysicists at ETH Zurich), which has been on the surface listening for signs of ‘martians’. The data set he collected (over 1,300 seismic events) has largely confirmed what planetary scientists have long suspected: that Mars is largely quiet.

However, a research team led by ETH Zurich recently analyzed a cluster of more than 20 recent earthquakes, which revealed something very interesting. Based on the location and spectral nature of these events, they determined that most of the widely distributed surface faults on Mars are not seismically active. However, most of the 20 seismic events observed came from the Cerberus Fossae region, an area made up of faults (or grabens). These results suggest that geological activity and volcanism still play an active role in shaping the surface of Mars.

The research was led by Simon C. Stähler, senior scientist in the Seismology and Geodynamics group at the Institute of Geophysics at ETH Zurich. His colleagues were joined by researchers from the Institute for Planetary Research (IPR) of the German Aerospace Center, Harvard University, the Laboratory of Planetology and Geodynamics (LPG) at the Université Paris Cité and NASA’s Jet Propulsion Laboratory. The paper describing their findings, “Tectonics of Cerberus Fossae unveiled by marsquakes,” recently appeared in the journal Astronomy of Nature.

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Mars Express image of the Tharsis region of Mars with several prominent shield volcanoes, including the massive Olympus Mons (left). Credit: ESA

Based on seismic data collected by InSight, the team concluded that low-frequency earthquakes could indicate the modern presence of molten magma in the Martian mantle. Specifically, they found that the epicenters of these earthquakes were mostly located in the inner part of Cerberus Fossae – at depths of 30 to 50 km (18.6 to 31 mi) below the surface. In this region, named after the inferno that guards the gates of Hades (the underworld in Greek mythology), the ground sinks under its own weight, simultaneously forming rifts that remove the crust of Mars.

The team theorized that these earthquakes could be the last rumblings from this once-active volcanic region, or that magma is moving eastward below the surface toward its next eruption. When the team examined orbital images of this area, they noticed that these earthquakes occurred very close to a structure in the Mantling Cerberus Fossae Unit (previously called a “young volcanic fissure”). This feature was surrounded by dark dust deposits, which existed in all directions and not just downwind (as expected).

As Stähler explained in a recent ETH Zurich press release, the only explanation for this was the presence of volcanic activity in the recent past. “The darker shade of dust means geological evidence of more recent volcanic activity – perhaps within the last 50,000 years – relatively recent, in geological terms,” ​​he said.

Because of its terrestrial (rocky) nature and its proximity to Earth, Mars provides opportunities to study geological processes similar to those that formed our planet. While technically closer, Venus’ extremely dense atmosphere prevents missions from studying it with anything other than surface-mapping radar and temperatures hot enough to melt lead. Because of their distance from Earth, which imposes communication delays, all other bodies in the Solar System have been studied only by orbiters and probes.

Relief map of the Martian surface showing InSight’s position (orange triangle) and the purple dots centered around Cerberus Fossae. Credit: Horelston et al. (2022) TSR

Additionally, Mars is the only terrestrial planet other than Earth known to have a core composed of iron, nickel, and sulfur that may have once supported a magnetic field. On Earth, this field results from dynamo action in the planet’s interior, where a liquid outer core rotates around a solid inner core (in the opposite direction to Earth’s rotation). It is now widely believed that about 4 billion years ago, the interior of the Red Planet cooled rapidly, causing the outer core to solidify while the inner core became molten. Without this field, the Martian atmosphere was slowly stripped away by the solar wind over eons.

Previously, scientists suspected that this also meant that Mars had died geologically billions of years ago. However, these and other clues provided by robotic missions suggest that geological activity has not completely ceased on the Red Planet. While significant research still needs to be done to confirm these results, the evidence of possible magma in the mantle of Mars today is exciting. These results demonstrate the effectiveness of the InSight lander and its sophisticated instruments, and how multiple robotic missions working together can lead to discoveries. Co-author Domenico Giardini said:

“InSight’s SEIS is the most sensitive seismometer ever installed on another planet. It gives geophysicists and seismologists the opportunity to work with current data that shows what is happening on Mars today – both on the surface and in its interior.”

In the coming years, many more robotic orbiters, landers and rovers will head to Mars. Their research into the surface geology, environment, climate and atmosphere of Mars will pave the way for crewed missions planned for the 2030s.

Further reading: ETH Zurich

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