The InSight Mars lander’s ultra-sensitive seismometer is protected from the elements by a domed wind and thermal shield. The instrument, provided by the French space agency, has detected three large marsquakes over the past month. Image: NASA/JPL-Caltech

On 18 September, the InSight Mars lander’s 1,000th day, or sol, on the surface of the red planet, the spacecraft detected one of the biggest, longest-lasting marsquakes yet, a temblor with an estimated magnitude of 4.2 that shook the ground for nearly 90 minutes.

It was the third major quake detected by InSight within a month following two temblors on 25 August that measured 4.2 and 4.1 respectively. For context, a magnitude 4.2 quake has five times the energy of InSight’s previous record holder, a magnitude 3.7 quake detected in 2019.

Scientists are still evaluation data from InSight’s Seismic Experiment for Interior Structure, or SEIS, instrument, provided by the French space agency CNES, to pin down the location of the 18 September quake. But they already know the larger of the two temblors detected on 25 August occurred about (8,500 kilometres (5,280 miles) from the lander – the farthest tremors yet felt.

The most powerful previously detected quakes occurred in the Cerberus Fossae region about 1,609 kilometres (1,000 miles) from InSight where lava may have flowed in the geologically recent past. An intriguing possibility is that the more recent quakes originated in the Valles Marineris region, the huge canyon system along the martian equator. The center of that system is about 9,700 kilometres (6,027 miles) from the lander.

The InSight lander as seen in a self portraint using a camera on the spacecraft’s robot arm. Image: NASA/JPL-Caltech

The two 25 August quakes were different types. The magnitude 4.2 quake featured slow, low-frequency vibrations while the magnitude 4.1 event, only 925 kilometres (575 miles) away, was marked by fast, high-frequency vibrations.

By studying seismic waves from marsquakes over a range of distances, scientists expect to learn more about Mars’ inner structure. The team already has determined the depth and thickness of the planet’s crust and mantle, along with the size of its still-molten core.

The team was fortunate to detect the most recent quakes. As Mars moved away from the sun in its elliptical orbit, more heater power was required to keep InSight warm. The power demand, in addition to dust buildups on the lander’s solar arrays, forced flight controllers to shut down various components to conserve energy.

But engineers managed to keep SEIS powered up by using InSight’s robot arm to trickle sand onto one array in hopes wind gusts would carry grains across the panel, knocking dust particles away. After several such dust-clearing attempts, power levels remained fairly steady,allowing the seismometer to remain in operation.

“If we hadn’t acted quickly earlier this year, we might have missed out on some great science,” said InSight’s principal investigator, Bruce Banerdt at NASA’s Jet Propulsion Laboratory. “Even after more than two years, Mars seems to have given us something new with these two quakes, which have unique characteristics.”





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