Researchers have discovered many recent Marsquakes on the Red Planet. Those shakes are likely signs that magma (岩浆) move deep under the Martian surface.
Since touching down on Mars four years ago, NASA's InSight lander has found more than 1,000 Marsquakes. One of its tools records quake waves. Those waves show information about a quake's size and location.
Earlier this year, scientists showed that several Marsquakes came from a particular part of Mars. It's known as Cerberus Fossae. Those quakes were a type pretty familiar to quake experts, states Anna Mittelholz, a planetary scientist at Harvard University. Their low-frequency waves "look much more like what we see for an earthquake," she says.
Mittelholz was part of a team that has studied many more Marsquakes. These include more than 1,000 high-frequency small quakes. The signals (信号) are fairly weak. To find out their origins, her team added the signals together. These quakes, too, seemed to come from the direction of Cerberus Fossae.
Scientists were surprised to find that different types of quakes all came from the same region on Mars. Previous research had suggested Marsquakes might be caused by the slow cooling and shrinking (收缩) of the planet's surface. That process, which also occurs on the moon, should produce quakes spread equally across the planet. As such, Mitteiholz says, "The expectation was that Marsquakes would come from all over the place."
Her team also compared the weak waves that InSight measured with those produced on Earth. Marsquakes looked like earthquakes that came from volcanic regions, the researchers found. That means Mars' shakes are probably produced by magma flowing tens of kilometers below the planet's surface.
Rather than being a geologically dead planet, as some have suggested, Mars might be surprisingly active, the researchers conclude (下结论). There's still so much more to learn about Mars, says Mitteiholz. "We're only touching the surface."
