The American probe InSight on the surface of Mars saw nothing with its own eyes, but it detected a faint tremor coming from the other side of the Red Planet. Five years after recording it, new analysis revealed that its source was a fault line moving deep within Vale Marineris, the largest known canyon system in the solar system.
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This means that this enormous rift, which formed billions of years ago, is not just a solid relic of Mars' past, but an area whose crust is still capable of fracturing and causing earthquakes.
The valley stretches for approximately 3,900 kilometers, is up to 600 kilometers wide, and reaches a depth of over 9 kilometers. Scientists had believed that the activity that created its main fissures had long since subsided, but an ancient signal offered a different perspective.
An earthquake revealed the movement of rocks deep underground.
Scientists named the quake "S0976a," and it was exceptional because it occurred far from the probe, in the western hemisphere of Mars. An approximate area of its source had been identified, but it was unclear whether it was caused by a rockslide, a meteorite impact, or underground fault movement.
The team studied how different types of seismic waves reach the only measuring instrument on the surface of Mars. The researchers compared the strength and direction of the vibrations to predictable patterns for each possible cause, then reviewed images of the area taken from orbit in search of a recent impact crater or large landslide.
The result was in favor of a tectonic earthquake that occurred at a depth of between 20 and 40 kilometers beneath the western part of the valley, near the area of Ios Kasma. The waves indicate the horizontal sliding of two blocks of crust along a steep fault, rather than a surface collapse.
Jung-Hoon Song, principal researcher at Imperial College London, said the area is not a "dead fossil landscape," explaining that ancient faults can move again after the major processes that formed them have ceased.
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