Through international collaboration, scientists find cause of InSight’s most powerful Marsquake

by Martijn Luinstra

An international team of scientists has found the cause of the largest Martian seismic event, or Marsquake, observed by NASA’s Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) Mars lander. After ruling out a meteor impact, they concluded the event must have been caused by a release of stress within the planet’s crust.

The forceful quake occurred on May 4, 2022, at 23:23 UTC, on the 1222nd Martian day, or sol, of InSight’s mission. The quake, also known as S1222a, was five times stronger than any event InSight had observed before. It shook the planet at a magnitude of 4.7 and the vibrations reverberated through Mars’ crust for approximately six hours.

The event showed similarities with earlier Martian seismic events, which have since been identified as meteor impacts, so scientists scoured the Martian surface for a possible impact crater. To do this, the team used observations from missions currently in orbit around Mars, engaging in an international collaboration between the European Space Agency (ESA), the Chinese National Space Agency, the Indian Space Research Organisation, and the United Arab Emirates Space Agency (UAESA).

“This project represents a huge international effort to help solve the mystery of S1222a, and I am incredibly grateful to all the missions who contributed,” said study lead Benjamin Fernando of the University of Oxford. “I hope this project serves as a template for productive international collaborations in deep space.”

The area that was imaged in the search for a possible impact crater. The yellow star shows S1222a’s expected epicenter and the yellow rectangle is the primary search area. A, B, and C show the observations and D shows the probability map for the event’s epicenter. (Credit: Fernando et al.)

For the largest meteor impacts detected by InSight, scientists found craters with a diameter of up to 150 meters. If S1222a was also caused by a meteor impact, the team expected to find a crater with a diameter of 300 meters and a blast zone that would be 180 kilometers across. Each contributing team looked for this potential crater using their spacecraft, comparing observations from before and after the Marsquake.

“We are willing to collaborate with scientists around the world to share and apply this scientific data to get more knowledge about Mars, and are proud to have provided data from the color imagers on Tianwen-1 to contribute to this effort,” said Jianjun Liu of Chinese Academy of Sciences.

But why did the team need observations from this many satellites?

“Making the association between a given seismic event and a fresh crater is challenging,” the scientists wrote. They can identify fresh craters by the presence of a blast zone, which fades over time but is easy to spot on lower-resolution images taken shortly after the impact. Depending on the impact terrain, however, blast zones can be obscured or less prevalent, so the team still needed high-resolution images to exclude the possibility of an impact.

Another challenge is the low availability of high-resolution images from spacecraft in orbit. The high-resolution cameras on the satellites have narrow fields of view and can only observe small areas at one time. Because of this, the region may not have been imaged before the impact, making it impossible for the teams to compare before and after photos in the search for a fresh crater.

To overcome these hurdles, the scientists had to look at the combined output of all current missions in orbit around Mars.

“This experiment shows how important it is to maintain a diverse set of instruments at Mars, and we are very glad to have played our part in completing the multi-instrumental and international approach of this study,” said Daniela Tirsch, Science Coordinator for the High-Resolution Stereo Camera onboard ESA’s Mars Express Spacecraft.

With all observations combined, the team found no evidence of an impact crater that could explain the measured seismic event and concluded that the Marsquake must thus have been a tectonic event in the planet’s own crust.

“We still think that Mars doesn’t have any active plate tectonics today, so this event was likely caused by the release of stress within Mars’ crust,” said Fernando “These stresses are the result of billions of years of evolution; including the cooling and shrinking of different parts of the planet at different rates.”

This Marsquake’s epicenter was located 2,200 kilometers from InSight, but well outside the Cerberus Fossae region which is known for its tectonic activity.

Map showing InSight’s location (red triangle), the location of S1222a’s expected epicenter (blue dot) and probability ellipse (blue), Cerberus Fossae (black lines) and the locations of other seismic events (purple dots). (Credit: Kawamura et al. (2023))

“We still do not fully understand why some parts of the planet seem to have higher stresses than others, but results like these help us to investigate further,” said Fernando. “One day, this information may help us to understand where it would be safe for humans to live on Mars and where you might want to avoid!”

The S1222a quake occurred near the end of InSight’s mission. By that time, some of the lander’s sensors were turned off to conserve power as dust had begun accumulating on its solar panels, reducing the lander’s available power to less than 20% of the original capacity. Because of this, Fernando’s team was limited to using seismic data, as no measurements of atmospheric pressure and wind were recorded.

InSight was launched on May 5, 2018, by the United Launch Alliance atop its Atlas V 401 rocket from Vandenberg Air Force Base in California. The mission landed in Mars’s Elysium Planitia region on Nov. 26, 2018. When NASA retired the lander in December 2022, it had detected 1,319 Marsquakes. Currently, scientists are continuing to analyze InSight’s data even after the mission ended.

“This has been a great opportunity for me to collaborate with the InSight team, as well as with individuals from other major missions dedicated to the study of Mars,” said Dimitra Atri of New York University Abu Dhabi, who contributed data from UAESA’s Hope Spacecraft. “This really is the golden age of Mars exploration!”

Fernando et al.’s study was published in Geophysical Research Letters on Oct. 17, 2023.

(Lead image: Illustration showing InSight on the Martian surface. Credit: NASA/JPL-Caltech)

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