New discovery about the properties of stones flown from the Moon

Future bases on the Moon and Mars will require materials, and we must minimize the resources we will have to transport from Earth to build them. Therefore, the development of recycling technologies is important. on the spot resources (ISRU). But to know how and why we can use these resources, we need to know their properties. Now, thanks to a new study, we know a little more about the rocks coming from the Moon.

We can know exactly the chemical and mineralogical composition of rocks on the Moon and Mars by studying fragments that reached Earth as meteorites and by analyzing lunar rocks brought back by astronauts from the Apollo missions.

Schematic diagram of the lunar ejecta resulting from the impact and the orbital transfer of material to Earth.
Trigo Rodríguez J.M., Peña Asencio E., Rimola A. et al. (2022)

In the laboratory we can study its mechanical properties: elasticity, ductility, malleability, ductility, hardness and brittleness.

So our new study of meteorites has revealed the characteristics of the most common minerals on the Moon and the asteroid Vesta: olivines, pyroxenes, feldspars and spinels.

Subject to the extreme conditions of space

Rocks on the Moon and Vesta have different mechanical properties than those on Earth.

For centuries, they were continuously bombarded by rocks up to one meter long, called meteoroids. Those larger than this diameter, asteroids, have excavated craters on the lunar surface and even launched some moon rocks into solar orbit. Moreover, these energetic processes resulted in the formation of impact fractures in many surface rocks, the components of which became mixed with the projectiles and were thermally altered during the impact process.

Lunar breccia, an important type of rock formed by compaction after successive impacts of lunar regolith.
Josep M. Trigo (CSIC-IEEC)

Bodies without an atmosphere, such as the Moon and Vesta, are also affected by the solar wind and cosmic radiation, which affects rocks at the nanoscale.

All these processes are grouped under the term “spatial processing” (in English: space weathering) and have profound implications for the properties of rocks we might one day want to use as a resource on the Moon.

Mechanical properties of lunar rocks

This will be the cover story in the new study. Meteoritics and planetologypreviously published on ArXiv, we analyzed the composition and mechanical properties of several lunar rocks that arrived on Earth as meteorites using our collection at the Space Science Institute (CSIC).

We needed to know its properties at the nanometer level. So we turned to a method that allows us to do this – nanoindentation, which we first used several years ago to study the mechanical properties of meteorites.

A mosaic of the lunar meteorite Dhofar 1084 from the Moon is shown in a typical nanoindentation plot (bottom left). The blue box shows its structure at the nanometer scale. In the lower right corner is a nanoindentometer and a pyramidal tip with which it applies pressure to a specific material (in blue).
Eloy Peña Asensio (CSIC-IEEC)

Explore rock at the nanoscale

Nanoindentation is a technique that allows force to be applied with great precision using a pyramid-shaped diamond tip onto a nanometer-sized surface. The controlled force is applied to specific, localized areas whose composition we know.

The diamond tip applies pressure to the surface, with the force gradually increasing to a predetermined maximum value. Subsequently, after the charging phase, it systematically decreases to zero. And the surface is compressed to a certain extent depending on the elasticity.

Thus, by studying this loading-unloading cycle, the device measures the penetration depth and draws conclusions about the plasticity of the rock. As a result of the study, conclusions can be drawn about the mechanisms of deformation (both elastic and plastic) and elastic recovery.

Discovery in lunar rocks

In summary, our work with lunar meteorites has revealed the inherent heterogeneity in the underlying mechanical properties of the most common minerals on the Moon and Vesta: olivines, pyroxenes, feldspars and spinel, even if they have similar mechanical properties.

Among the differences found, olivines of terrestrial origin are harder than olivines of lunar origin.

Our research also indicates that the absence of an atmosphere on the Moon and Vesta, and their exposure to sudden and very energetic meteorite impacts, results in fragmentation, rupture and increased natural porosity of the minerals from which rocks are formed. This parameter is key to explaining the mechanical properties of rocks.

Our results have direct implications for the development of new recycling methods. on the spot resources (ISRU). In turn, they are important for better understanding how craters are excavated and how some of these rocks travel at super speeds, defying the gravitational field of their bodies.

The mechanical characteristics of the rocks that form these planetary bodies will be useful for conducting exploration on the Moon or even for carefully addressing the challenges and opportunities associated with mining in space.

The Apollo 16 mobile lunar rover on a mountainside near the Descartes crater landing site.

Differences with Earth

Mechanical properties are key to densification and sintering processes (manufacturing objects using heat), which will allow, for example, the creation of stronger and more durable building materials in these extreme conditions. This is why it is important to do more research looking at how the porosity and crystalline structure of rocks affect their mechanical properties.

The future creation of sustainable infrastructure, roads and other vital structures needed for long-term human presence on the Moon or Mars will require materials, and the best ones need to be identified before embarking on the journey.

New challenges for humanity, which will little by little become multi-planetary.

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