On November 26, 2018, NASA’s Interior Exploration mission using Seismic Investigations, Geodesy, and Thermal Transport (InSight) touched down on Mars. This was a major milestone in the exploration of Mars, as it was the first time a research station was placed on the surface to study the planet’s interior.

One of the key tools InSight used to do this was the Heat Flow and Physical Properties Package (HP).³It was developed by the German Aerospace Center (DLR). This device, also known as the Mars Mole, has been measuring heat fluxes from deep within the planet for four years.

HP³ It was designed to dive up to five meters (~16.5 feet) below the surface to more deeply feel the heat of Mars’ interior. Unfortunately, the Mole tried to dig and ended up falling just below the surface, much to the scientists’ surprise. Still, Mole collected important data about daily and seasonal changes below the surface.

Analysis of these data by a team from the German Aerospace Center (DLR) has provided new insights into why the Martian soil is so “crystalline”. According to the findings, temperatures in the upper 40 cm (~16 inches) of the Martian surface lead to the formation of salt films that strengthen the soil.

The analysis was published in the journal Geophysical Research LettersIt was carried out by a team from the Microgravity User Support Center (MUSC) of the DLR Space Operations and Astronaut Training Institute in Cologne, which was responsible for the supervision of the HP experiment.³.

Temperature data obtained from the subsurface could be an integral part of understanding the geological evolution of Mars and evaluating theories about its central region. Scientists currently suspect that geological activity on Mars largely ceased during the late Hesperian period (about 3 billion years ago), but there is evidence that lava still flows there today.

This was probably because Mars’ interior cooled faster due to lower mass and lower pressure. Scientists speculate that this causes Mars’ outer core to solidify and its inner core to become liquid, but this is still an open question.

By comparing the subsurface temperature obtained by InSight with the surface temperature, the DLR team was able to measure the heat transfer rate (coefficient of thermal conductivity) and thermal conductivity in the crust. Thus, for the first time, it was possible to estimate the density of Martian soil.

The team determined that the density of the top 30 cm (~12 inches) of soil was comparable to basaltic sand; this was not predicted based on orbital data. This material is common on Earth and is formed by the weathering of volcanic rocks rich in iron and magnesium.

The density of the soil below this layer is comparable to compacted sand and coarser pieces of basalt. Tilman Spohn, principal investigator of the HP experiment³ The DLR Institute for Planetary Studies explained in a DLR press release:

“To get an idea of ​​the mechanical properties of soil, I like to compare it to floristic foam, which is commonly used in flower arrangements in floriculture. It is a lightweight, highly porous material that forms holes when plant stems are pressed into… We measured thermal conductivity and temperature fluctuations at short intervals during seven days on Mars.

“We also measured the highest and lowest daily temperature continuously during the second Martian year. The average temperature at the depth of the 40-centimeter thermal probe was -56°C (217.5 Kelvin). These records document the temperature curve in diurnal cycles and seasonal variations, and It was the first of its kind in . “

Since the crust-covered Martian soil (called “duricrus”) extends to a depth of 20 cm (~8 in), the Mole only reaches slightly more than 40 cm (~16 in), i.e. well over 5 m (~16.5 ft). managed to penetrate underneath. ). Nevertheless, data obtained at this depth provided valuable information about heat transport on Mars.

Accordingly, the team found that ground temperatures fluctuate by only 5 °C to 7 °C (9 °F to 12.5 °F) over the course of a Martian day; this is a fraction of the 110 °C to 130 °C variation seen at the surface. °C. (230°F to 266°F).

They observed seasonal temperature variation of 13°C (~23.5°F) below the freezing point of water in the near-surface layers on Mars. This suggests that Martian soil is an excellent insulator, greatly reducing large temperature differences at shallow depths.

This affects various physical properties of Martian soil, including elasticity, thermal conductivity, heat capacity, movement of material within it, and the speed at which seismic waves can travel through it.

“Temperature also has a strong influence on the chemical reactions occurring in the soil, the exchange with gas molecules in the atmosphere, and thus the potential biological processes for possible microbial life on Mars,” Spohn said. “This understanding of the properties and strength of Martian soil is also of particular interest for future human exploration of Mars.”

But what was particularly interesting was how temperature fluctuations in winter and spring allowed the formation of salty brine for 10 hours a day (when there was enough moisture in the atmosphere). Solidification of this brine is therefore the most likely explanation for the hard crust layer beneath the surface. This information could be very useful as future missions explore Mars and attempt to delve beneath the surface to learn more about the Red Planet’s history.