Millions of miles away, a robot geologist stands alone on the dusty surface of Mars, listening for faint seismic echoes in the ground below. Its finger on the red planet’s pulse is sensitive enough to pick up the whoosh of wind, the drone of dust devils, the creak of tectonic cracks, and many other rumbles ricocheting though the planet’s insides.

While most of these signals have been indistinct murmurs, two have stood out loud and clear, allowing scientists to trace them back to their source: the first active fault zone yet found on the red planet.

Known as marsquakes, the events clocked in between magnitude 3 and 4, according to data from NASA’s InSight lander presented at a