NASA discovered many huge "marsquakes" on Mars. These are the greatest earthquakes ever recorded on the planet, with magnitudes of 4.1 and 4.2 on the Richter Scale.
In November 2018, NASA's InSight lander landed on Mars, carrying the world's most sensitive seismometer.
Since its arrival, the mission has detected a slew of events known as marsquakes, which it has used to map the planet's interior.
According to scientists on the mission, the two newly publicized quakes were exceptional.
Researchers unveiled this astonishing revelation in the journal Seismic Record, with the study title "The Far Side of Mars: Two Distant Marsquakes Detected by InSight."
People watch the landing of NASA's InSight spacecraft on the planet Mars on television screens at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California on November 26, 2018. - Cheers and applause erupted at NASA's Jet Propulsion Laboratory as a $993 million unmanned lander, called InSight, touched down on the Red Planet and managed to send back its first picture.
NASA InSight Lander Detects 2 Marsquake on Far Side of Red Planet
Space.com said the first earthquake, dubbed S0976a, struck on Aug. 25, 2021, with a magnitude of 4.2. It originated in the Valles Marineris, a massive network of canyons that stretches 2,500 miles (4,000 kilometers) on the far side of the planet from InSight.
The Valles Marineris is a graben system, a valley with discrete fault blocks considerably lower than the blocks on either side. The Martian canyon complex is one of the largest graben systems in the solar system. Although prior orbital photography of the Valles Marineris had indicated the aftermath of seismic activity on Mars, such as faults and landslides, the 2021 observation is the first time an event has been recorded at this site.
S1000a, the second marsquake, struck 24 days later, on Sept. 18, 2021. This quake was slightly smaller, measuring magnitude 4.1, and the specific location of the marsquake is uncertain. However, scientists have pinpointed it to Mars' far side. S1000a was also the longest seismic event yet recorded on Mars, lasting 94 minutes.
Both marsquakes occurred in a seismic shadow zone, a region where InSight's seismometer cannot detect P and S waves, which are the two primary forms of pressure waves produced by an earthquake. Since these waves are blocked from reaching the seismometer by Mars' core, researchers concentrate on PP and SS waves.
PP and SS seismic waves, unlike conventional P and S seismic waves, are reflected at the surface and are not interrupted by the planet's core. Therefore, they can provide information regarding how a quake moves over the surface, horizontally and vertically.
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How to Detect Marsquakes
The mechanics that cause marsquakes and earthquakes are remarkably similar except for a few fundamental changes.
Moonquakes, for example, are more concentrated at a vast depth-between 600 and 1000 kilometers-than earthquakes. The discrepancies in seismic energy release distribution and magnitude on the earth and the moon are most likely due to fundamental changes in internal dynamics.
All of this is fascinating, but the two recently discovered marsquakes differ in other ways. S0976a, for example, like many of the quakes discovered so far on the planet, is characterized by only low-frequency energy. The frequency spectrum of S1000a, on the other hand, is vast.
Anna Horleston of the University of Bristol, from the research team, said (via Interesting Engineering): "[S1000a] is a clear outlier in our catalog and will be key to our further understanding of Martian seismology."
She believes that S0976a has a far deeper genesis than S1000a.
The latter event, according to the researcher, had a frequency spectrum that is much more similar to a family of events that we witness that have been modeled as shallow, crustal quakes, suggesting that it happened near the surface.
S0976a appears to be similar to many of the events we've seen around Cerberus Fossae - an area of significant faulting - that have depths of 50 kilometers or more, and it's likely that this event has a deep source mechanism as well.
The two additional far-side quakes, according to the scientists, are true outliers when compared to the rest of the seismic activity identified by InSight.
Not only are they by far the most extensive and farthest events, but S1000a also has a spectrum and duration unlike any other previously seen event. Horleston continued that these are absolutely exceptional events in the Martian seismic database.
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