For the first time since its mission began, NASA's InSight lander has detected what scientists believe to be a marsquake, NASA announced Tuesday. The spacecraft has been on the surface of Mars since November as part of an ongoing mission to listen for quakes on the red planet.

The probe's seismometer (SEIS) has been active since December, but only recorded the first quake on April 6, on the 128th Martian day (or sol) of the mission, according to a press release by France's space agency, CNES, which built the device. It was a small quake — it wouldn't have even registered on Earth — but a major step for the lander's overall mission.

"We've been waiting months for our first marsquake," said Philippe Lognonné, SEIS team lead at the Institut de Physique du Globe de Paris (IPGP) in France. "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 modelled our data."

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

While the slight quake could have been caused by wind or other external forces, the InSight team is "confident" it came from Mars itself. However, the quake was too small to to provide data on the Martian interior, one of InSight's main goals. The seismometer has measured three other signals of activity since the initial one, but they have all been much weaker than the first.

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The marsquake is comparable to seismic activity measured on the moon during the Apollo missions, between 1969 and 1977. During that time, astronauts measured thousands of quakes.

"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. "We've been collecting background noise up until now, but this first event officially kicks off a new field: Martian seismology."

Unlike Earth, Mars and the moon lack tectonic plates, so their quakes are caused by faults, or fractures, in their crusts. Luckily, the Martian surface is much quieter than Earth, which is how the seismometer was able to pick up on such faint rumbles.

In a recording released by NASA, three distinct sounds can be heard: the Mars wind, the supposed quake and the lander's robotic arm moving to take pictures. Because the actual vibrations would be undetectable to the human ear, the sound recording has been sped up by a factor of 60.