After landing on Mars last November, the InSight probe first deployed a suite of meteorological equipment and then began to check the health of its science instruments. Following this, the NASA lander extended its French-made seismometer to the red planet's surface in December, then commissioned the instrument in early February.

InSight began listening. Finally, on April 6, the seismometer detected a weak but distinct seismic signal. It was, scientists concluded, a shaking of the ground coming from the interior of the world, not due to some external factor such as wind.

"We've been waiting months for our first marsquake," said Philippe Lognonné, the principal investigator for the seismometer mission, which was developed by the French space agency CNES. "It's so exciting to finally have proof that Mars is still seismically active. We're looking forward to sharing detailed results once we've studied it more and modeled our data."

Of course, scientists have measured earthquakes on our own planet for more than a century. And astronauts Neil Armstrong and Buzz Aldrin deployed a seismometer on the Moon in 1969, nearly 50 years ago, to study the internal structure of the Moon. They found an incredibly geologically active world.

Mars, I hear you. I've detected some quiet but distinct shaking on #Mars. The faint rumbles appear to have come from the inside of the planet, and are still being studied by my team. Take a listen.👂https://t.co/GxR1xdRx1F pic.twitter.com/Z8Hn03jigO — NASA InSight (@NASAInSight) April 23, 2019

The French scientists, in conjunction with NASA, found that the marsquakes resembled those that occurred on the Moon.

"InSight's first readings carry on the science that began with the Apollo missions," said InSight Principal Investigator Bruce Banerdt of NASA's Jet Propulsion Laboratory in Pasadena, California. "We've been collecting background noise up until now, but this first event officially kicks off a new field: Martian seismology."

This marsquake was not strong enough to tell scientists much about the interior of Mars, but they expect future, stronger quakes to provide this information.

Meanwhile, NASA and its international partners are continuing to troubleshoot a probe known as the "mole," which is a part of the lander designed to dig up to five meters into the surface to provide additional information about the Martian interior. Shortly after beginning to hammer itself into the surface two months ago, the mole's progress stopped, and scientists are investigating whether the probe has struck a rock or a layer of gravel that is impeding its progress.