Before the InSight Lander arrived on Mars, scientists could only estimate what the planet’s internal structure might be. Its size, mass, and moment of inertia were their main clues. Meteorites, orbiters, and in-situ sampling by rovers provided other clues.
But when InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) arrived on Mars in November 2018 and deployed its seismometer, better data started streaming in.
One of the most compelling questions about Mars is “what happened to its magnetosphere?” Earth’s magnetosphere keeps our planet habitable and has for billions of years. Our planet’s rotating, convective outer core is the dynamo responsible for the magnetosphere. Evidence shows that Mars used to be habitable, so it must have had a magnetosphere and a liquid rotating core. Magnetization in Martian rocks tells us that. But what happened to it?
To answer that, we need better data on Mars’ interior, and NASA and the DLR sent InSight there to get us the data. Its three primary instruments are SEIS (Seismic Experiment for Interior Structure,) HP3 (Heat Flow and Physical Properties Package,) and RISE (Rotation and Interior Structure Experiment.) The most ambitious of the three instruments was HP3, which needed to burrow into the ground to gather its data. Sadly, HP3 failed, but the other instruments are still working.
SEIS plays a significant role in a new study examining marsquakes. It’s a seismometer, and it measures marsquakes, meteorite impacts, and other internal activity by monitoring seismic waves.
The new study is “Repetitive marsquakes in Martian upper mantle,” The lead author is Weijia Sun, from the Institute of Geology and Geophysics at the Chinese Academy of Sciences. The co-author is Professor Hrvoje Tkalcic from the ANU Research School of Earth Sciences. The study is in the journal Nature Communications.
This is a visualization of a marsquake that originated in Cerberus Fossae. It’s not one of the 47 in this study, but it shows how InSight can detect and map marsquakes.
Most of what we know about Mars’ internal structure comes from physical parameters provided by astronomical and orbital measurements. NASA’s Viking Landers carried seismometers, but they were largely ineffective. They weren’t deployed directly on the ground. Instead, they remained on the lander decks, and the Martian wind degraded their data. Viking 1’s seismometer failed, but Viking 2 did detect one marsquake, and that data limited Mars’ seismicity to levels much lower than the Earth’s.
InSight’s SEIS instrument is a huge improvement on the Viking Landers’ seismometers, but it has its limitations. Marsquakes have relatively small magnitudes compared to Earthquakes, so their seismic waves can be scattered or lost in the noise. This leads to uncertainties, especially when it comes to their exact locations. And since InSight’s SEIS instrument is the only recording station, it’s difficult to pin down each quake’s physical cause. That makes it hard to determine the nature of Mars’ deep interior, and it’s challenging to come to any inferences or conclusions on the activity in Mars’ mantle.
Viking’s seismometer (left) sat on the lander deck and was exposed to wind, degrading its data. InSight’s sesimometer is deployed on Mars’ surface under a protective wind shield. Image Credits: (l) NASA; (r) NASA/DLR.
The researchers wanted to dig deeper into the SEIS data in this study. They thought there might be more marsquakes hidden in the data, which both automated algorithms and manual searches missed. “Therefore,” they write, “there is the need to complement the existing searches with dedicated searches for potential, smaller marsquakes buried in noisy waveforms.”
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