It really cannot be said that Mars would be stingy with news this year: The Chinese Zhurong Rover has now covered more than half a kilometer and found its parachute, among other things, the Mars helicopter Ingenuity is daring ever more complex flight maneuvers, Perseverance is just beginning collecting rock samples, and the Arab Mars probe has sent first samples of its scientific instruments. Now the scientists of NASA's InSight mission, which landed on Mars in 2018, are also reporting new results in the journal Science. The SEIS instrument was on board at that time, a seismometer that has since been able to detect many Martian quakes: a large number of weak quakes in the crust,plus a small number of stronger ones with deeper origins - that was announced last year.
Sibylle Anderl
Editor in the features section.
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On the basis of these previous measurements, three studies have now reconstructed the previously little-known interior of Mars.
Understanding this is important in order to be able to trace the formation of the planet, its tectonics and volcanism and the development of its global magnetic field.
A group led by Simon Stähler from ETH Zurich used the deep Mars quakes to understand the properties of the planetary core. Seismic waves thrown back at the core suggest a radius of this central area of around 1830 kilometers, whereby the core, which consists largely of iron and nickel, still appears to be liquid. This is a bit larger and less dense than previously thought. It must therefore also contain lighter elements such as sulfur. The data also suggest that Mars - unlike Earth - does not have a dense, heat-insulating layer of the mineral bridgmanite in its mantle that could have prevented the interior of young Mars from cooling rapidly.
This, in turn, is important information if one is to understand the history of the magnetic field on Mars. Ancient magnetized crustal rock indicates that this magnetic field was once as strong as on Earth. For the first few hundred million years it was found to be generated in the rapidly cooling core by a thermally powered dynamo, later presumably by changes in the composition and state of the core, before it finally disappeared 3.7 billion years ago. This led to the fact that Mars became a hostile, dry desert, as the solar wind could now contribute unhindered to allow the atmosphere to escape into the interplanetary space.
Scientists working with Amir Khan, also from ETH Zurich, devoted their study to the upper rock layer down to a depth of 800 kilometers. Their measurements suggest that the outermost solid and static area, the lithosphere, is much thicker than on Earth. When trying to reproduce this structure of Mars using models of its thermal development history, they found that there must be 13 to 20 times as many radioactive and thus heat-producing elements in the crust as in the mantle.
A third group led by Brigitte Knapmeyer-Endrun from the Bensberg earthquake station in Bergisch Gladbach finally examined the Martian crust. In the history of the Red Planet, this outer layer formed early and under the influence of strong volcanism. In the seismic data, the researchers found evidence of either two or three crust layers below the landing site, according to which the crust there would be either around 20 or 39 kilometers thick. In both scenarios, the crustal rock would be less dense than the surface material - an indication that this rock has been repeatedly changed over time by geological processes, so that porous rock, liquids or fill rock of low density could form. The new information should helpTo further improve models of the interior of Mars and its development. More data will follow: The InSight mission is to continue until the end of 2022.