The InSight lander took this selfie in its first weeks on Mars, before it deployed its seismic instrument.Credit: NASA/JPL-Caltech

NASA’s InSight lander has detected the first known ‘marsquake’.

The spacecraft picked up the faint trembling of Mars’s surface on 6 April, 128 Martian days after landing on the planet last November. The quake is the first to be detected on a planetary body other than Earth or the Moon.

The shaking was relatively weak — similar to that of moonquakes that Apollo astronauts measured in the late 1960s and early 1970s.

“We thought Mars was probably going to be somewhere between Earth and the Moon” in terms of seismic activity, says Renee Weber, a planetary scientist at NASA’s Marshall Space Flight Center in Huntsville, Alabama. “It’s still very early in the mission, but it's looking a bit more Moon-like than Earth-like,” she says.

It’s not yet clear whether the shaking originated inside Mars or was caused by a meteorite crashing into the planet’s surface, sending ripples thorugh its interior.

David Mimoun, a scientist with the mission at the French National Higher Institute of Aeronautics and Space in Toulouse, says the signal is too weak to have been detected on Earth. “It’s so small that at the beginning we were wondering if it was a quake or something else,” he says.

Ears to the ground

InSight heard the marsquake using a French-built seismometer that contains three extremely sensitive sensors nestled inside a dome to protect them from the wind. Mission scientists had previously observed vibrations caused by the Martian wind blowing overhead. But the seismic characteristics of the 6 April event show that it came from inside the planet.

“This signal was not like anything we’d seen before,” says Mark Panning, a planetary seismologist at NASA’s Jet Propulsion Laboratory in Pasadena, California.

Team scientists can’t tell where the quake originated. Determining that would allow them to trace how the seismic energy radiated through the planet, and to begin to understand Mars’s interior structure — InSight’﻿s main goal. The spacecraft is meant to operate for about one Martian year, or nearly two Earth years. “We’ve got time,” says Panning. “In my ideal universe, Mars would be having giant marsquakes all the time.”

InSight has detected three other possible marsquakes, on 14 March, 10 April and 11 April. But they were even fainter than the 6 April event and their source is still unclear.

The spacecraft is working on Elysium Planitia, a plain near Mars’s equator. Mission controllers are still trying to work out how to unstick its German-built heat probe. It became lodged on what is probably a buried rock in February, as it tried to hammer itself into the ground to measure temperatures there.