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Humanity knows 5,600 minerals. This is what it says on the lists of the International Mineralogical Society. We are even directly responsible for the creation of around 200 of them, for example through mining and industrial activities. A European research team led by Jörg Fritz, a visiting scientist at the Ries Crater and Impact Research Center in Nördlingen, has described a hitherto completely unknown connection in the journal “American Mineralogist”.
What’s special about this: The mineral, consisting of calcium, aluminum, silicon and oxygen atoms, was found in lunar rocks. It is called Donwilhelmsit, after the American lunar explorer Don E. Wilhelms. The now 90-year-old geologist was part of the science team for the “Apollo” missions. “We wanted to name the mineral after someone who is still alive and can be happy for him,” says discoverer Fritz in an interview with SPIEGEL.
The substance does not come from the material that astronauts collected on the moon back then. It was detected in the 400 gram meteorite Oued Awilits 001. This stone was once thrown from the Earth’s satellite by an impact and landed here on earth after a trip through the solar system.
In total, researchers know about 360 lunar meteorites, the first known specimens were discovered about 40 years ago in Antarctica. They are of interest to science, especially since previous lunar missions have only collected samples from a fraction of the lunar surface. Meteorite rock cannot be exactly mapped to a place of origin on the moon, but it certainly also covers areas for which there are no other samples.
The specimen currently under examination was discovered in January 2014 during an expedition to Western Sahara. Some of it was bought with the help of a crowdfunding campaign for the Vienna Natural History Museum and is on display there. However, the museum has just closed due to the corona pandemic.
The impact on the moon didn’t just send the meteor on its way towards us. He also made sure that the mineral formed inside it, because the rock was briefly exposed to 240,000 times the pressure on the surface of the earth. This created so-called fusion crash zones in the material. In such an area of the rock, Fritz found tiny needles when examining under the microscope, which after spectroscopic analysis turned out to be extremely interesting. Colleagues, among others at the Museum für Naturkunde Berlin and the German Research Center for Geosciences in Potsdam, helped show that it was actually a separate mineral. Last year the International Mineralogical Society recognized Donwilhelmsite as a novelty, but now the team only provides the exact scientific description.
The mineral is also found deep in the Earth’s mantle.
Particularly interesting: the conditions that allowed the mineral to form on the Moon, extremely high pressures and temperatures, correspond to those found at a depth of 400 kilometers inside the Earth. Because there is also Donwilhelmsite there, but no one has seen it yet: the mineral is formed on earth from remains of continental crust. These first end up as sediments on the ocean floor. Later, tectonic plates link them to the oceanic crust deep in the earth’s mantle. There, the rock changes with increasing pressure and temperature, and minerals such as Donwilhelmsite are formed.
In general, in the earth’s mantle there are numerous minerals such as wadsleyite, ringwoodite and bridgmanite, which only form under extreme conditions. However, researchers can only produce the compounds in small amounts in high-pressure experiments, or look for them in meteorites, as Fritz and his colleagues did. The pieces of the moon are particularly interesting due to the complexity of the rock.
“An overwhelming feeling”
Ansgar Greshake, Scientific Director of the Meteorite Collection at the Museum für Naturkunde Berlin, is one of the co-authors of the current work. He says, “I’ve been working with meteorites every day for 25 years, but suddenly being the first to discover a new mineral from space and then exploring it is an overwhelming feeling.”
Fritz, the study director, is particularly pleased to have worked with colleagues across Europe for the publication for four years. His main job is that of director of an auteur cinema in Heppenheim, Hesse. It’s been in the family for 100 years, he explains. After his previous job as a full-time scientist, including at the Museum für Naturkunde Berlin, he decided to take over cinema, without giving up his passion for meteorites: “We are the auteur cinema with the most articles on planetary science”, jokes Fritz .
