On November 26, 2018, the InSight lander, from NASA, ended its trip to Martian territory. Thus began a mission whose main purpose was study the interior of Mars. This would be done mainly through the measurement of three types of parameters: the temperature at 5 meters deep, the wobble on its own axis and the seismic waves. Now, almost three years later, an international team of scientists will publish three studies in which the conclusions of the analysis of these latest data are exposed.
Two of them have had Spanish participation, with the intervention of the seismologist Martin Shimmel, of the Institute of Geosciences of the CSIC. In addition, the Spanish Astrobiology Center (CAB) has also participated with the design of an essential instrument for the correct development of these measurements.
Together, all these scientists from different parts of the globe have achieved something that had not been achieved before: obtain direct measurements of the interior of another planet. Let’s see what these measurements are.
How has InSight been able to get to the depths?
We still have a lot to know about the interior of Mars thanks to InSight. At the moment, they are seismic data those who have given us more information. This is so because they have been able to analyze seismic waves, reflected and modified by the internal structures of the red planet.
At this point, as he has narrated to Hypertextual Martin Shimmel, the role of TWINS. This is an instrument, developed by the CAB, that includes wind and temperature sensors. It is very necessary because the wind measurements, among others, help to “verify that the seismic waves that are observed are not generated by lander winds and vibrations”.
We start with the crust
“Until now, all missions to Mars were focused on the surface study from a satellite or the surface itself ”, says Shimmel. Therefore, it is the first time that direct measurements of the interior of mars or from any other planet.
In fact, they have obtained very specific data, both from the Cortex as from mantle and the nucleus. For the first, they have calculated that it must have a thickness of between 20 and 39 kilometers in the place where the InSight lander. Based on these estimates, global gravity and topography limit the mean thickness of the global crust at 24 – 72 km”. On the other hand, they have also calculated its density, which must be found between 2,850 and 3,100 kg / m³, based on cortical thickness. This, as Shimmel explains, is a lower figure than estimated; since, as a result of the analysis of the composition of the surface materials, it was calculated that it would be about 3,300 kg / m³.
The seismologist interviewed by this means points out that all this information is very important, because “knowing the thickness of the crust limits the way the planet differentiated and evolved over time”.
Mantle and core, the depths of the interior of Mars
For the core, consisting of Liquid metal, they have calculated that it must have a radius of approximately 1,830 kilometers. Studies prior to the analysis of the interior of Mars by InSight estimated that it would be between 1,400 and 2,000 kilometers. Therefore, in this case the estimates are correct. As they count in a Press release of the American Society for the Advancement of Science, “Begins roughly halfway between the surface and the center of the planet, suggesting that the planet’s mantle consists of a single rocky layer, instead of two, as on Earth ”.
In addition, Martin Shimmel adds that all this gives data on the composition of said nucleus. “A core with a radius smaller than about 1600 km would be deficient in light elements and would allow the existence of a lower and upper mantle similar to that of the Earth. Instead, a large nucleus would be enriched with light elements and excludes the presence of the lower mantle ”.
On the other hand, to learn more about the mantle of the interior of Mars, they have studied the direct and reflected seismic waves on the surface of eight Martian earthquakes (marsquakes) low frequency. Thus, they have been able to probe deeper and reveal the structure of the mantle at a depth of almost 800 km. This has allowed them to observe a thick lithosphere, some 500 kilometers below the surface.
These three studies, which are published in Science, are the first fruits of the work of InSight. But he still has a lot to tell us, so we will have to remain vigilant to continue learning about what is happening inside Mars.