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NASA's InSight Receiver places a domed protective shield over its seismometer.
JPL-Caltech / NASA
By Paul Voosen
WOOD, TEXAS-After months of tricky maneuvers, the NASA InSight lander has finished placing its hypersensitive seismometer on the surface of Mars. The instrument is designed to solve the mysteries of the interior of the planet by detecting the thunder of "marsquakes". But just weeks after it went into service, the car-sized undercarriage has already heard something else: the whistles that continually shake our red neighbor. . If Marsquakes is the drum solo, these microseisms, as they are called, constitute the bass line.
The signal appeared for the first time in early February, as soon as the lander placed a protective shield on the seismometer, said Philippe Lognonne, planetary seismologist at the University of Paris Diderot, at the head of the team that manages the 'instrument. the annual conference on lunar and planetary science. "We think these signals are waves coming from Mars." This is the first time, he said, that such micro-phenomena have been detected on another planet.
On Earth, microseisms are ubiquitous, largely due to the ocean sliding by storms and tides. Despite the dreams of sci-fi writers, Mars does not have a current ocean. Instead, this newly discovered noise is probably caused by low-frequency pressure waves from atmospheric winds vibrating on the surface, inducing longer, longer-lasting surface waves, called Rayleigh waves, Lognonné said.
Although InSight has not yet detected a marsquake, microseisms are an important indicator of how well the LG seismometer works. In recent decades, seismologists have begun to consider microseism on Earth as a nuisance, but also as a valuable tool for understanding the characteristics of the subsoil. This noise will be just as valuable on Mars, said Lognonné, allowing the seismologists on the team to probe the rigid surface crust in the immediate vicinity of the landing gear.
But the seismometer has had little time to listen until now. While the sand-filled crater where InSight landed, nicknamed "Homestead Hollow", had few large rocks to complicate its placement, the deployment took another month longer than expected, thanks to two tricky tasks. First of all, scientists had to carefully adjust the electrical cable connecting the seismometer to the undercarriage, to reduce the noise coming from the undercarriage. Then they had to place a wind and heat shield on the instrument.
Since then, InSight has spent a lot of time troubleshooting its second instrument, a thermal probe designed to burrow up to 5 meters below the surface. The robotic arm placed this instrument in mid-February. But shortly after the probe began pounding the surface, its 40-centimeter "mole" was stuck on a rock or other obstacle only 30 centimeters deep. Now, the mission's scientists have suspended work until agency engineers evaluate their options. This will continue for many more weeks, said Bruce Banerdt, principal investigator of InSight and geophysicist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.
Although microseisms are a pleasure to hear, all those working on InSight are waiting for the main event: their first marsquake. No need to panic for not seeing more, Banerdt said. "Before getting nervous … [the mission is] exactly where we expected. The team expects to detect about one marsquake per month, but these will probably come in clusters, not perfectly spaced. Banerdt, who has been preparing this mission for decades, can be patient, he said. "The wait is not yet completely over."
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