Scientists know this because they sent a seismometer to our planetary neighbor. The instrument arrived last year, on board a NASA lander called InSight. The seismometer, small and dome-shaped, has sat on the brick-colored surface since, waiting for hints of movement below the surface. On April 6, it caught something, a “quiet but distinct” signal, scientists said. A rumble from the depths. [...]
Scientists have suspected for decades that they’d find this phenomenon if they had the right tools to look. Unlike Earth, Mars lacks tectonic plates that glide over its mantle, jostling the ground when they touch. But like Earth, Mars has three distinct layers—a rocky crust, a mantle, and a metal core—and it’s still cooling from its fiery formation out of a primordial cloud of cosmic dust. Even now, billions of years later, heat radiates from its center and can be strong enough to crack the surface and escape. The fracturing sends seismic waves streaming in all directions. [...]
While scientists are thrilled about the detection, they wish the rumble were stronger. The quake measured about 2.5 on the Richter scale, too weak to draw a path within the depths. If a tremor like that happened on Earth, you wouldn’t feel it. If you were standing next to the InSight lander at the moment of detection, you wouldn’t know either. “We are waiting for the big, big one,” says David Mimoun, a scientist at France’s Higher Institute of Aeronautics and Space and a member of the seismometer team. Researchers expect to detect dozens more, some as powerful as 5.5 magnitude.
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