Three things NASA learned from Mars InSight

NASA’s InSight spacecraft reached Mars on November 26, 2018 to study the deep interior of the planet. Just over a Martian year later, the stationary lander detected more than 480 earthquakes and collected the most comprehensive meteorological data of any surface mission sent to Mars. The InSight spacecraft, which struggled to dig underground to take over the planet’s temperature, has also made progress.

There was a time when the surfaces of Mars and Earth were very similar. Both were warm, humid and shrouded in thick atmospheres. But 3 or 4 billion years ago, these two worlds took different paths. The mission of InSight (short for Inner Exploration using seismic investigations, geodesy and heat transport) was to help scientists compare the Earth to its rusty brother. Studying what the depth of Mars is made of, how the material is layered, and how quickly heat flows from it could help scientists better understand how a planet’s starting materials make it more or less likely. to support life.

Although there are several sciences from InSight, here are three discoveries about our red neighbor in the sky.

Low noise is the norm

The InSight seismometer, which was provided by the French space agency, the Center National d’Études Spatiales (CNES), is sensitive enough to detect slight noises from long distances. But it was not until April 2019 that seismologists from the Marsquake Service, coordinated by ETH Zurich, detected their first marsquake. Since then, Mars has made up for more time lost, shaking frequently, albeit lightly, without earthquakes larger than magnitude 3.7.

The lack of earthquakes larger than magnitude 4 is a mystery, given how often the Red Planet shakes due to smaller earthquakes.

“It’s a little surprising that we haven’t seen a larger event,” said seismologist Mark Panning of NASA’s Southern California Jet Propulsion Laboratory, which leads the InSight mission. “That might tell us something about Mars or it might tell us something about luck.”

In other words, Mars may just be more static than anticipated – or InSight may have landed in a particularly quiet period.

Seismologists will have to continue to wait patiently for those larger earthquakes to study the deep layers under the crust. “Sometimes you get big flashes of amazing information, but most of the time you erase what nature has to tell you,” said JPL chief investigator Bruce Banerdt of InSight. “It’s more like trying to follow a clue of complicated clues than presenting the answers in a nicely packaged package.”

The wind can hide earthquakes

Once InSight began detecting earthquakes, they became so regular that at one point they happened every day. Then, at the end of June this year, the detections essentially stopped. Only five earthquakes have been detected since then, all since September.

Scientists believe that the wind on Mars is responsible for these seismically empty periods: the planet entered the windiest season of the Martian year around June. The mission knew that the winds could affect InSight’s sensitive seismometer, which is equipped with a dome shield for wind and heat. But the wind still shakes the earth itself and creates a literal noise that covers earthquakes. This could also have contributed to what appears to have been the long seismic silence before the first InSight earthquake, since the ship landed as a regional dust storm set in.

“Before landing, we had to guess how the wind would affect the surface vibrations,” Banerdt said. “Because we work with much smaller events than we would pay attention to on Earth, we find that we need to pay much more attention to the wind.”

Surface waves are missing

All earthquakes have two sets of body waves, which are waves that travel through the interior of the planet: primary waves (P waves) and secondary waves (S waves). They also curl along the tip of the crust as part of a third category, called surface waves.

On Earth, seismologists use surface waves to learn more about the planet’s internal structure. Before reaching Mars, InSight seismologists expected these waves to provide deep glances about 400 kilometers below the surface, in a sub-crustal layer called the mantle. But Mars continues to offer mysteries: despite hundreds of earthquakes, none have included surface waves.

“It’s not totally unheard of to have earthquakes without surface waves, but it was a surprise,” Panning said. “For example, you can’t see surface waves on the moon. But that’s because the moon has many more scatterings than Mars.”

The dry lunar crust is more fractured than Earth and Mars, causing seismic waves to jump around them in a more diffuse pattern that can last more than an hour. The lack of surface waves on Mars may be related to extensive fracturing in the first 6 miles (10 kilometers) below InSight. It could also mean that earthquakes detected by InSight come from the depths of the planet, as they would not produce strong surface waves.

Of course, revealing such mysteries is what science means and there is much more to come with InSight.

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