NASA's Insight lander was sitting silently in the empty dust plains of Mars as it had for the past 1,000 Martian days, when the ground began to rumble. The shaking continued for nearly an hour and a half.
Two other big ones recently rolled through, too: On August 25, the lander felt two quakes of magnitudes 4.2 and 4.1.
InSight's Dusty Selfie (Credit: NASA)
InSight has detected more than 700 quakes in total, and they've revealed a lot about the planet's interior already. Scientists have learned that Mars' crust is thinner than they thought, and that it's more like the moon's crust than Earth's — it's broken up from asteroid impacts.
Because the Martian crust is so dry and broken, its quakes last much longer than earthquakes.
Recently, scientists have also used the quakes to determine that Mars has a molten core. They're not yet sure whether a solid inner core hides beneath a molten outer core, the way it does on Earth.