The main objective of the mission has been achieved”, said Philippe Legnona, geophysicist at the Institute for Physics at the World in Paris (IPGP) and scientific director of the Mars Seismometer. more (Seismic experiments for indoor facilities), during a press conference on 21 July 2021 at IPGP. Launched and stored on Mars in December 2018 by NASA InSightInland exploration using seismic investigations, geodesy and thermal transport), a seismometer manufactured by Philippe Legnonier reveals, for the first time, the internal structure of the red planet. The thickness and division of the crust in particular, but also the structure of the mantle, the heat flux out of the planet’s core and the size of the core, the results of two years of detailed measurements and analyzes in several publications from the journal Science July 23, 2021. So, among these crops, “This is the size of the heart of Mars – much bigger than expected! – This is the biggest surprisePhilippe Legnonier points out.
Ultrasound usus Mars
Little is known, so far, about the bowels of Mars. Estimates of the core radius are between 1,600 and 1,900 kilometers, which is a very wide range. Planetary scientists have speculated about its composition and wondered if it was still liquid and whether it was made, like Earth, from a solid seed surrounded by a liquid envelope. Analysis of seismic waves recorded during a Martian year (that is, about two Earth years) has answered most of these questions.
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“This is the same principle as ultrasoundexplains Rafael Garcia, professor at the Higher Institute of Aeronautics and Astronautics (ISAE-SUPAERO) in Toulouse and co-investigator of the InSight mission. Certain seismic waves are reflected from the surface of the core, at the interface with the mantle. They are then captured by a seismometer and thus their properties provide valuable information about the dimensions and properties of the core.. ”
Waves that do not propagate in a liquid medium
Six seismic waves called “shear”, which have the peculiarity of their inability to propagate in a liquid medium and therefore reflected in it, are analyzed very carefully. Thanks to them, geophysicists were able to determine that the Martian core was eventually liquid, at least part of the surface. Also thanks to this wave, they were able to calculate the radius of the nucleus with unprecedented accuracy: 1830 kilometers plus or minus 40 kilometers, shows one publication. Science, “The error bar has been reduced by a factor of about 10 compared to the previous analysis“, Raphaël Garcia rejoiced. Thus, the Martian core occupies 53% of the total radius (3,390 km). Therefore, it is very large and massive, in a higher range than scientists thought, and has a relatively low density: between 5.7 and 6.3 grams per cubic centimeter according to the researchers’ calculations.
Diagram struktur internal Mars (S. Stähler and others./Science)
The nucleus contains carbon and oxygen and
Rafael Garcia says that this means that “Mars’ core, in addition to the iron and nickel that also make up Earth’s core, contains large amounts of light elements: possibly sulfur, but also carbon, oxygen, or hydrogen.. “A lot of information will, from now on, be explained by researchers, which will allow for a better understanding of how the Red Planet formed 4.5 billion years ago and then evolved. A large core could explain, in particular, why this planet formed. seems to have lost its global magnetic field in its youth. On Earth, the magnetic field generated by this convective motion within the core acts as a shield: it deflects the lethal particles of the solar wind and is an important component in the evolution of life. Mars, the presence of a large core clearly did not allow the formation of a dense and viscous undercover, which isolates it from the rest. The planet facilitates convective motion as is the case on Earth, and thus this discovery more easily explains how the magnetic field could have existed early in the history of Mars before disappearing. when the core heat is adequately evacuated.
Great wait
Moving forward, and figuring out, in particular, whether Mars’ core is a solid “seed” like Earth’s, scientists have two possibilities.
The first, impossible given the data recorded so far by InSight’s seismometers, is that a very strong earthquake (magnitude 4 or even 5) rocked the bowels of Mars. “Then a seismic wave would strike the core with a force like a hammer on a bell, causing the entire planet to ring and give an indication of the presence or absence of a solid seed.”Rafael Garcia explained.
The second possibility: installing another seismometer on the surface of Mars by a new space mission, to make it work in the network and extract more detailed information. This is one of the goals of the future Russian-European Exomars mission, which will carry the rover Rosalind Franklin as well as a Russian-made seismometer. If all goes according to plan, the mission will fly to Mars in 2022.
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