Mars's gigantic canyon is not completely dormant.
Valles Marineris stretches across the Martian surface for nearly 4,000 kilometers. Some of its valleys are several kilometers deep. This immense network of canyons formed billions of years ago, when the planet's crust stretched and fractured. It is therefore reasonable to ask whether these ancient cracks are still evolving.
Three-dimensional modeling of the Valles Marineris terrain on Mars, created using mapping data from the JMARS software.
Illustration: Nathanial Bradford.
One answer comes from a quake detected on August 25, 2021, by InSight, NASA's probe that listened to vibrations in the Martian ground. At the time, it recorded a signal coming from very far away, without researchers being able to determine precisely what had caused it.
A new analysis has located its origin near the western part of Valles Marineris, in the Ius Chasma region. The vibrations appear to have come from a fault several dozen kilometers beneath the surface, probably between 20 and 40 kilometers deep according to the models.
The researchers studied how the waves traveled through Mars. Their calculations indicate that two blocks of rock slid horizontally against each other. This is a movement also observed during some earthquakes on Earth, even though the causes are different.
Historic orbital view of Valles Marineris, the network of canyons that stretches across the Martian surface for nearly 4,000 kilometers.
Credit: NASA, Viking mission, public domain.
On Earth, the large plates that make up the surface move relative to one another. Mars does not have comparable plate tectonics. Its interior is cooling slowly, and stresses left by its geological history can still cause old faults to move.
The team also checked other possibilities. A meteorite impact or a gigantic landslide could have produced the tremors. But these scenarios explain the recorded signal less well. Images taken from orbit also show no new trace corresponding to a major collapse.
For now, only one quake has been clearly attributed to this region, and InSight was very far away: many small tremors could have gone unnoticed. Nevertheless, this event demonstrates that not all ancient Martian fractures are frozen in place.
Mars therefore remains a planet that is evolving, even without widespread volcanism or the movement of large plates as on Earth. Understanding where its faults are still moving will help scientists reconstruct its history and better assess the risks for future exploration missions.