On September 18, the 1,000th day of the InSight Mars, or ground, lander on the surface of the Red Planet, the spacecraft detected one of the largest and longest earthquakes to date, a tremor with an estimated magnitude of 4.2 that shook the ground for nearly 90 minutes.
It was the third major earthquake detected by InSight in a month after two tremors on August 25 measuring 4.2 and 4.1 respectively. For context, a magnitude 4.2 earthquake has five times the energy of the previous InSight record holder, a magnitude 3.7 earthquake detected in 2019.
Scientists are still evaluating data from the InSight Interior Structure Seismic Experiment Instrument, or SEIS, provided by the French space agency CNES, to determine the location of the September 18 earthquake. But they already know that the larger of the two tremors detected on August 25 occurred about (8,500 kilometers (5,280 miles) from the lander – the most distant tremors ever felt.
The strongest earthquakes previously detected occurred in the Cerberus Fossae region about 1,609 kilometers (1,000 miles) from InSight, where lava may have flowed in the geologically recent past. One intriguing possibility is that the most recent earthquakes originated in the region of Valles Marineris, the immense system of canyons along the Martian equator. The center of this system is approximately 9,700 kilometers (6,027 miles) from the lander.
The two earthquakes of August 25 were of different types. The 4.2 magnitude quake featured slow low frequency vibrations while the 4.1 magnitude event just 925 kilometers (575 miles) was marked by rapid high frequency vibrations.
By studying seismic waves from earthquakes over a range of distances, scientists expect to learn more about the internal structure of Mars. The team has already determined the depth and thickness of the planet’s crust and mantle, as well as the size of its still molten core.
The team had the chance to detect the most recent earthquakes. As Mars moved away from the sun in its elliptical orbit, more heating power was needed to keep InSight warm. The demand for power, in addition to the build-up of dust on the lander’s solar panels, forced flight controllers to shut down various components to save power.
But engineers were able to keep SEIS powered up by using InSight’s robotic arm to pour sand over a grid in the hope that the gusts of wind would carry grains through the panel, repelling dust particles. After several attempts at dusting, the power levels remained fairly stable, allowing the seismometer to continue operating.
“If we hadn’t acted quickly earlier this year, we might have missed out on some great science,” said InSight principal investigator Bruce Banerdt of NASA’s Jet Propulsion Laboratory. “Even after more than two years, Mars seems to have given us something new with these two earthquakes, which have unique characteristics.”