First "marsquake" detected on the red planet

The NASA InSight lander has detected the first known "marsquake".

The spacecraft detected the slight tremor of the surface of Mars on April 6, 128 days after landing on the planet last November. The earthquake is the first to be detected on a planetary body other than the Earth or the Moon.

The shaking was relatively weak, announced the French space agency CNES April 23. The seismic energy it produced was similar to that of the moonquakes measured by Apollo astronauts in the late 1960s and early 1970s.

"We thought Mars would probably be somewhere between the 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. "The mission is still in its infancy, but it looks a bit more like a moon than a land," she says.

It is not yet clear whether the unrest took place on Mars or was caused by a meteorite that crashed to the surface of the planet.

David Mimoun, a scientist assigned to the Higher Institute of Aeronautics and Space in Toulouse, France, says the signal is so weak that it would not have been detected on Earth. "It's so small that at the beginning we were wondering if it was an earthquake or something else," he says.

Ears on the ground

InSight heard the earthquake with the help of a French-made instrument containing three extremely sensitive seismometers tucked into a dome to protect them from the wind. Mission scientists had previously observed vibrations caused by the Martian wind overhead. But the seismic features of the April 6 event show that it was coming from inside the planet.

"This signal was unlike anything we had seen before," says Mark Panning, a planetary seismologist at NASA's Jet Propulsion Laboratory in Pasadena, California.

The scientists on the team can not say where the earthquake came from. Determining this would allow them to trace the way seismic energy was radiating across the planet and to begin to understand the inner structure of the planet – the primary goal of InSight. The spacecraft is supposed to work for a Martian year, or nearly two terrestrial years. "We have time," says Panning. "In my ideal universe, Mars would have giant marsquakes all the time."

InSight has detected three more possible Marchquakes on March 14, April 10 and 11. But they were even weaker than the event of April 6 and their source is still unknown.

The probe is working on Elysium Planitia, near the equator of Mars. Mission controllers are still trying to find a way to take off the German-built thermal probe. He was lodged on what is probably a rock buried in February, while he was trying to sink into the ground to measure temperatures.