What will NASA InSight find on Mars

NASA probe Insight explores the red planet : The quakes of Mars

Even if no life has been proven on Mars so far, it is a living celestial body, at least from a geological point of view. Some volcanic eruptions are only a few million years old and there is evidence that magma is still active underground to this day. And the planet is regularly shaken by marsquakes.

This is shown by observations of the NASA-led mission “InSight” (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport), which are now being presented in the specialist magazine “Nature Geoscience” (in several specialist articles: 1, 2, 3, 4, 5, 6 ).

For the first time it succeeded meaningful seismic measurements on Mars, explains the Max Planck Institute for Solar System Research (MPS) in Göttingen, which is involved in the mission.

Launched two years later, costing $ 150 million more

The “Viking” probes from the 1970s already had seismometers on board. But these were firmly connected to the landing unit and - as it turned out later - only recorded how the Martian wind shook the probes. The InSight seismometer, called SEIS, on the other hand, was set down in the Martian sand with a gripper arm and also protected from the wind by a hood.

The device, built by the French space agency CNES, is highly sensitive, which caused difficulties in advance. "InSight" was originally supposed to start in 2016, but the vacuum chamber for the seismometer was not tight, so NASA decided to postpone the start by two years and to undertake a redesign.

The additional costs amounted to around $ 150 million. It was not until November 26, 2018 that the lander touched down near the equator on the Red Planet.

The trouble was worth it, SEIS works reliably. The present publications refer to this period from February to September 2019 174 seismic events detected. Since then, the measurements have been continued and a total of 450 events have been recorded, which have not yet been fully evaluated, according to ETH Zurich, which is also involved.

Corresponding about one quake a daythat SEIS can perceive. Extrapolated to the entire celestial body, the quake activity is greater than previously estimated, the released seismic energy lies between that of the very inert moon and the dynamic earth.

Mars has only one plate

Our planet consists of tectonic plates that move against each other and thus lead to many earthquakes. Mars probably only has one plate. "But tremors can also occur within a plate, as we know from Earth," says Ulrich Christensen from MPS, one of the leading SEIS researchers.

There are two main reasons for the marsquake. “The planet is cooling down and shrinking,” explains the researcher. "Since the outer crust is brittle, tensions arise in it until it finally breaks and the subsurface trembles." The second possibility is convection currents in the deep, plastic mantle, which influence the crust and stretch it, for example. "We know that from the Vallis Marineris, an extensive rift system."

Of the recorded marsquakes, the three strongest occurred in the Cerberus Fossae region, which is around 1,600 kilometers away and also represents a tectonic rift system. The strength of the earthquakes, however, is low. Between April and September 2019, a good 20 were recorded with a magnitude between 3 and 4, which roughly corresponds to the value that a person can feel.

None came above magnitude 4. However, the measurement period is relatively short. Stronger quakes, which are rarer, are quite possible, explains Christensen. Weaker earthquakes were identified primarily at night, as the strong winds during the day interfere with the measurements too much.

The researchers can use the seismic data to estimate the structure of the subsurface: the earthquake waves are transmitted at different speeds depending on the material properties and are reflected and refracted at boundary layers.

In contrast to seismic studies on Earth, where there are many stations spatially distributed, Mars researchers have to get by with just one device. That complicates matters.

Heat build-up inside Mars

“We cannot yet say how thick the crust of Mars is,” says Christensen. It is clear, however, that the top ten kilometers are very rugged, primarily due to numerous meteorite impacts, and below that, more compact rock adjoins.

One floor below, in the upper mantle of Mars, the researchers found that the seismic waves were significantly attenuated. That probably goes on one Heat build-up back, who heats up the material and makes it softer, explains Domenico Giardini from ETH Zurich, who headed the evaluation. "Since Mars does not have plate tectonics, heat from the inside - caused by radioactive decay today and compression during the formation of the planet - can only very slowly be transported through the crust to the outside," he wrote in an email.

In the lower part of the Martian mantle, on the other hand, the attenuation seems to be significantly lower than what we know from Earth. “If this were to be confirmed by further Mars quakes, that would tell us something about the temperature inside Mars, for example that the Coat is comparatively cooler than that of the earth.“

Earthquake measurements should support the search for life

Nicholas Schmerr of the University of Maryland, who is also on the mission, says the earthquake analysis could also help answer the big question about life on the planet - by using seismological data to narrow down the origin of the tremors.

"Just think of hydrothermal sources on the mid-ocean ridges of the earth, where chemistry is more likely to provide the necessary energy for life than sunlight," the geologist is quoted in a statement from his institute. “If it turns out that there is liquid magma on Mars and we can pinpoint exactly where the planet is most geologically active, that could be used as a basis for the goals of future missions that the potential for life want to explore. "

Things are also turbulent on the surface of the planet. InSight has measured more than 1,000 small-scale cyclones that swept over him at the Elysium Planitia site. It is thus the most active of all previous landing sites of Mars missions. It would be expected that at least some of these eddies take up fine sediment and form so-called dust devils.

It's just strange that InSight didn't capture a single one of them with its cameras. The researchers speculate whether either not enough material was thrown up to spot the dust devils, or whether it was simply bad timing and the devils were missed. Future observations may be more successful.

A mole that doesn't want to dig

The team of the thermal probe HP3 has even bigger bad luck. The device from the German Aerospace Center (DLR) is supposed to propel itself into the ground with the help of a striking device and measure the heat flow in the depths. The plan was to penetrate three to five meters into the sand.

But the "Mars mole" came just a little bit ahead and worked his way partly off the ground again out. For over a year now, the researchers have been trying various tricks, for example by holding onto the lander's shovel, to get the “mole” down.

"Right now we have reaches a depth of around 30 centimeters“, Reports the project manager Tilman Spohn from DLR in Berlin. He continues to hold on to the target of three to five meters in order to obtain the heat flow data he was hoping for.

But the chances are falling. NASA has already reduced the communication options with the probe - sending commands and receiving data. "If we don't make clear progress by the end of spring, it will probably be over“Says Spohn. The mission goal would have to be finally given up.

A lot has been learned about the properties of the Martian soil in the past few months and will be published soon, says Spohn. “But that is only a small consolation.” A new blade position is currently being tried out. Maybe it will work with it.

According to the current status, the main InSight mission should run until November. An extension is being discussed, yes new robots are coming soon: Two rovers are set to set off for Mars this summer: the European ExoMars rover "Rosalind Franklin" with its landing platform "Kazachok" from Russia and the Mars 2020 rover from NASA. Both missions are scheduled to arrive in March and February 2021, respectively. Both rovers have various cameras and analysis devices to examine the surface more closely.

ExoMars is also supposed to clarify whether there was life on the planet under more favorable conditions in primeval times. Proof of life that has survived to this day is not possible with both rovers - unless a green man waves into one of the cameras.

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