Last week, NASA reported the first observation of an “earthquake” on Mars, which was detected by the Seismic Experiment for Interior Structure (SEIS) instrument on the InSight lander. This “marsquake” was very weak by terrestrial standards — a mere 2.5 on the Richter magnitude scale – undetectable by a human, and weaker than many instruments on the Earth would be able to separate from background noise. Only through the extraordinary precision in designing and building the SEIS instrument and through careful correction for vibrations generated Mars’ winds was this first ever detection possible. Although it was a small event, the signature of this marsquake will provide a unique look into the Martian interior. As the mission continues, subsequent detections will help us refine that look and come to a better, and more detailed, understanding of the inside of Mars.