Neil Armstrong and Buzz Aldrin had received a scientific to-do list for their moon landing in the course of the Apollo 11 mission, the chronological order of which corresponded to the priority of the respective tasks. The first thing to do on the lunar surface was to collect about a kilogram of lunar rock that was supposed to be stowed in Armstrong’s suit and that would have been transported back to earth even if the field was abandoned prematurely. It was hoped that these rock samples would provide the greatest scientific benefit from the moon landing. Ultimately, there was even enough time for Aldrin and Armstrong to assemble a total of around 20 kilograms of lunar material from the Mare Tranquillitatis. The sample laid the foundation for a series of groundbreaking new discoveries about the earth’s satellite and its history.
Another five Apollo missions and three Soviet Luna missions brought much more rock from the moon up to 1976, around 400 kilograms of which exist on earth today. If you want to do research on NASA samples, you have to write a scientific application and, if successful, get access to tiny amounts of the precious material. Even today these samples continue to generate new insights into the nature of our earthly companion and the history of the solar system.
The moonstones have preserved their history in a unique way. Unlike on Earth, no recent geological activity and – due to the lack of a lunar atmosphere – no weathering has been able to destroy this information in the past billions of years: for example, its origin in the early magma ocean of the moon or its chemical change due to massive meteorite impacts. Surface rubble, the regolith, also bears traces of its interaction with radiation and particles that come from the sun and from more distant regions of the cosmos. It is littered with holes made by tiny meteorites that never reach our earth due to their atmosphere.
A puzzle piece to understand the history of the moon
Moonstone comes in many different varieties: basaltic volcanic rock, which once crystallized from a hot magma liquid and provides information on the chemical composition of the interior of the moon, compounds of minerals such as feldspar, spinel or olivine, and glass beads formed in meteorite impacts under high temperatures and pressure Debris of existing breccia rock or old anorthosite, which makes up a large part of the crust of the highland regions. Each type of rock has its own story and in turn provides a piece of the puzzle for understanding the history of the moon.
This understanding has been fundamentally put to the test several times during the rehearsals of the Apollo missions. At first it was assumed that the moon and earth differed fundamentally in their composition. For example, the average density of the moon is only 60 percent as great as that of the earth; compared to the earth, it has hardly any iron, water and volatile elements. Attempting to match these differences with a plausible history of its formation eventually led to the idea that a third body must have played a role in the formation of the moon, from which the moon could have inherited its chemical characteristics.
Do the models of moon formation need to be modified?
The dramatic impact of a Mars-sized body, called Theia, on the newly formed earth, in which the moon was largely formed from the mantle material of the impact body, then became the standard theory of moon formation. However, analyzes of the Apollo samples showed that there is a problem with this story: In one respect, the earth and moon are significantly more similar than they should be according to the Theia collision. The distribution of chemical variants of oxygen, its isotopes, is practically identical in the rock of both bodies. Theia, on the other hand, should have had a completely different isotope distribution, since it was not formed in the same place as the earth. The idea that the moon was made for the most part from Theia’s material therefore seems too simple. So do the current models of moon formation have to be modified?