NASA scientists are still in the midst of sussing out the exact cause of the rumbling. Here on Earth, quakes happen when tectonic plates grind up against one another. But trembles on Mars, which lacks tectonic plates, seem to have a different origin: The planet is still gradually cooling down—and temperature changes cause its rocky crust to contract and crack, resulting in occasional quivers. Quakes can also be triggered by meteors impacting Mars’ surfaces, though, and that possibility hasn’t been ruled out.

By studying Mars’ subtle shaking, researchers hope to better understand the planet’s structure and composition. Depending on the materials they pass through, seismic waves behave differently—and gathering this kind of data could help scientists figure out how Mars and other rocky bodies in our Solar System formed.

Already, the April 6 quake has stirred a bit of intrigue. It seems the tremor occurred relatively close to the lander, and lasted for more than 10 minutes—a long time for shaking that would have been pretty much imperceptible on our own planet. Protracted rumbling could indicate that the ground beneath InSight holds little water, which muffles seismic waves, or that the makeup of its soil differs vastly from what’s here on Earth.

That’s about all researchers know so far. Unfortunately, this quake wasn’t quite strong enough reveal anything deep beneath the Red Planet’s surface. But the fact that it happened at all is encouraging—simply because it’s unlikely to be a one-off event.

Plus, there are already hints of a repeat. InSight tuned into three other sets of seismic signals on March 14, April 10, and April 11. But these other potential marsquakes, which are still unconfirmed, were even smaller and more ambiguous in origin than the April 6 tremor.

The hope is that a dozen more marsquakes will occur before the lander reaches the end of its tenure. InSight is scheduled to operate for two more (Earth) years. If its solar-powered instruments continue to behave, though, that period could lengthen. “It’s a waiting game...we just have to wait until the planet cooperates,” NASA planetary scientist Amy Weber told Julia Rosen at the Los Angeles Times.

There’s no telling what’s to come—but on this foreign, distant world, every bit of information makes a difference. “[InSight is] helping paint the picture that Mars is still an active place,” Tanya Harrison, a Mars scientist at Arizona State University, told Maya Wei-Haas and Michael Greshko at National Geographic. “We’ve just been building incrementally onto this story.”

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