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The surface of Mars (archive image)
Photo: JPL-Caltech / ASU / MSSS / NASA
Aside from his piano, the earth is actually a pretty dust-free place, Bruce Banerdt recently said.
It is different on Mars, where the dirt is "definitely one of our greatest challenges."
Geoscientist Banerdt is responsible for the scientific output of the Mars probe »Insight« at the Jet Propulsion Laboratory in Pasadena, California.
The experts are currently grappling with a rather annoying problem: the wind and electrostatic forces of attraction on the solar panels of the robot that landed in November 2018 caused large amounts of dust to build up. Around 80 percent of the area is already covered in this way, says Banerdt. The current yield has dropped rapidly recently. In the worst case, the US space agency Nasa will have to announce the end of the mission in April.
»Insight« has been working longer than originally planned. The probe has already been able to collect a lot of important data on the internal structure of the red planet. The teams involved are now presenting the knowledge they have gained in three separate articles in the specialist magazine "Science". The most important message: The structure of the red planet is quite similar to our earth, but it has a larger core and a thinner crust than previously assumed.
The research is based on the evaluation of more than two years of measurement data from the seismometer built in France on »Insight«. In addition to the - overall rather hapless - Mars mole for measuring the heat distribution in the ground, for which the German Aerospace Center (DLR) was responsible, it was one of the two main instruments of the probe. The highly sensitive seismometer listened for vibrations in the underground of Mars. The scientists had hoped to hear the impact of meteorites. So far, however, this has not worked out without a doubt.
The interesting thing is that the seismometer can only measure well when the Martian weather is right.
"Half of the day is so windy that the seismometer can only detect very strong tremors," says Simon Stähler from ETH Zurich in an interview with SPIEGEL.
Otherwise the gusts cause disturbing noises.
Stähler is the lead author of one of the articles that have now been published.
More than 700 quakes are now in the researchers' catalog and could now be used for the evaluation.
Built like a peach
"The three studies provide important information about the structure of Mars today and are also the key to a better understanding of how the planet formed billions of years ago and how it evolved over time," write Sanne Cottar and Paula Koelemijer from the university in Cambridge, UK, in an accompanying commentary in Science.
Our earth is made up of three shells: on the very outside, i.e. directly under our feet, is the very thin crust of light, brittle rock. It's like the skin of a peach. Below is the earth's mantle made of heavy, plastically deformable rock. If you want to stay in the picture of the peach, it represents the pulp. And again underneath is the core. In the case of Earth, it consists largely of the elements iron and nickel. Researchers assumed a similar structure for Mars - and have now been able to confirm this assumption in principle.
"We now have another strong indication that the core of Mars is actually liquid," describes researcher Stähler. And it is also comparatively large: "According to our measurements, the core of Mars has a diameter of almost 3,700 kilometers," says co-author Ana-Catalina Plesa from the DLR Institute for Planetary Research in Berlin. "That is about half the core diameter of the earth and is rather at the upper end of the size range that all previous estimates had shown." To classify: The diameter of Mars at 6770 kilometers is also about half the diameter of the earth.
At around six grams per cubic centimeter, the Martian core has a significantly lower density than our Earth's core, which is around 9 to 13 grams per cubic centimeter.
This means that deep inside our neighboring planet, in addition to iron and nickel, lighter elements such as sulfur, carbon, oxygen or maybe even hydrogen are likely to occur.
Big differences in crust thickness
"There are also interesting new findings for the crust of Mars and the mantle underneath," says Brigitte Knapmeyer-Endrun from the Bensberg earthquake station at the University of Cologne. She is the first author of another study that has now been published. How thick the crust is at the landing site of »Insight«, there are two options: either 20 or 40 kilometers. The result depends on the interpretation of the seismic signals. It seems clear, however, that the crust is definitely thinner overall than previously assumed - and that its extent is likely to vary considerably depending on its position on Mars.
The mantle of Mars, in turn, according to the researchers, can be compared to a simpler version of the earth's mantle.
The outer skin of the Red Planet consists largely of the mineral olivine, as does the Earth's upper mantle.
Bridgmanite, one of the most common minerals on our planet, but which hardly anyone knows because it only occurs further down in the mantle, should not play a major role on Mars.
For their further work, the teams hope that »Insight« will hold out for as long as possible.
At NASA, a maneuver that appears paradoxical at first glance has recently been tried out to help with this.
One could summarize it under the slogan "cleaning by dirtying".
Space engineers used the shovel of "Insights" to pick up the robotic arm Mars sand from the vicinity of the landing site.
Then they let it trickle down again not far from the dirty solar panels - at a time with as much wind as possible.
In the process, some grains hit the solar panels and freed them from particularly fine dust particles that had previously been deposited there.
The maneuver caused at least a "small increase" in the electricity yield, explained chief scientist Banerdt afterwards cautiously.
You have a little leeway that you didn't have before.
ETH geo researcher Stähler, on the other hand, says: "That brought us a few extra months, we'll be through by the end of next year."
