NASA’s InSight lander reveals details of Mars’ outer layer

By Will Dunham

WASHINGTON – NASAThe InSight rover, in the twilight of its service after nearly four years on Mars, is revealing new details about Earth’s nearest planetary neighbor based on data from two large meteorite impacts that shed light on the structure of Mars’ crust.

Researchers said Thursday that the stationary lander detected for the first time seismic waves traveling along the Martian surface, as opposed to those deeper in the planet’s body, caused by two space rocks that hit Mars in September and December. last year. The reverberation of these waves along the surface gave clues to the crust, the outermost layer of the planet, over a wide geographical area in the northern hemisphere.

These were the largest impacts detected by InSight since it arrived at Mars in November 2018. Its science mission – originally planned to last two years but then extended for another two through December – is expected to end because the solar Its panel is now covered by accumulated dust, depriving InSight of power.

Seismic waves generated by earthquakes and surface shocks vary in speed and shape as they travel through different material within a planet. Data collected by InSight’s seismometer instrument helped scientists decipher the internal structure of Mars, including the size of its liquid metallic core, the nature of its mantle and the thickness of its crust.

InSight also found that Mars is seismically active by detecting more than 1,000 earthquakes, the largest of which came in May of this year with a magnitude of 5.0 – medium in size compared to earthquakes on Earth.

“InSight was successful beyond my expectations,” said planetary geophysicist Bruce Banerdt of NASAJet Propulsion Laboratory, the principal investigator of the InSight mission and co-author of the new research published in the journal Science. “We are probably in the final phase of the mission.”

The InSight tripod – short for Interior Exploration Using Seismic Investigations, Geodesy and Heat Transport – sits on a vast and relatively flat plain called Elysium Planitia, just north of the Martian equator.

Until now, InSight had obtained data on the structure of the Martian crust – which is mainly composed of fine-grained volcanic basalt rock – only in the area below the actual landing site.

Previous findings indicated that the crust at the landing site consisted of relatively soft material, less dense rock. This was not the case for the other areas covered by the new data, where the crust appears denser.

There are two main types of seismic waves. Surface waves travel along the surface of a planet like ripples in water. Body waves travel through the inner layers of a planet.

“As a consequence of our analysis of surface waves, we now understand that the Martian crust north of the equatorial divide – a prominent feature seen in the topographic variation on Mars that separates the southern highlands and northern lowlands – has a relatively uniform structure. ,” said seismologist Doyeon Kim of the Institute of Geophysics at ETH Zurich, lead author of the study.

The data examined depths between 3 and 19 miles (5-30 km) below the surface.

The earth’s crust is divided into huge plates that inevitably move over a rocky inner layer called the mantle in a process known as plate tectonics. The crust in some places under the Earth’s oceans is constantly being recycled. Mars lacks tectonic plates.

“The crust of Mars is ancient and probably similar to Earth’s crust in its early stage,” Kim said.

The December 2021 impact spotted by InSight left a crater about 490 feet (150 meters) in diameter. The September 2021 crater was about 425 feet (130 meters) wide.

“Two very large meteor impacts occurred within 90 days,” said planetary scientist and study co-author Simon Staehler of ETH Zurich Seismology and Geodynamics Group. “This is important in terms of the risk perspective for possible future exploration of the planet, and we need to understand if this was a one-off or if it happens more often on Mars.”