The right stone is from the meteorite that fell from the sky on September 28, 1969, near the Australian city of Murchison. Photo:, in the public domain
The small chunk looks like a piece of gravel from the railway embankment, not exactly like a scientific sensation. But the potato-sized black stone has an ancient history: it goes back even further than the time of origin of our solar system. This formed 4.56 billion years ago from an accumulation of dust particles. The dust itself had a journey of millions of years and was made up of the remnants of exploded and disintegrated stars. Researchers at the Max Planck Institute (MPI) for Chemistry in Mainz can now reconstruct many details of his history thanks to sophisticated measurement technology. The most recent date in this story is the easiest to name: On September 28, 1969, a 100-pound meteorite fell from the sky near the Australian city of Murchison. The Mainzer rock is one of the fragments of this so-called Murchison meteorite. The meteorite has proven to be a true treasure for research, reports the astronomer and science journalist Thomas Bührke in an article in the December issue of the science magazine "bild der wissenschaft".

"It contains tiny mineral granules that have been proven to be created in the vicinity of aging and exploding stars, " explain Ulrich Ott and Peter Hoppe from the Mainz MPI in "Bild der wissenschaft". After the end of these stars, the grains traveled through the Milky Way and became part of the Solar Mist, which eventually formed the Sun, Earth, and all other celestial bodies of our solar system.

Scientists had long suspected that this nebula would have consisted of a homogeneous mixture of dust particles. But in the 1960s, the analysis of a meteorite showed that it contained the noble gas xenon in a completely different isotopic composition than in other known finds. In another meteorite, scientists discovered unusually large amounts of the isotope neon-22. The results indicated that the physical-chemical fingerprint of the stars, from which the material originated in solar fog, can still be read in the individual particles to this day.

The amount of analysis and measurement technology and the knowledge that researchers like Ott and Hoppe from the MPI in Mainz have to spend on this search for clues are, of course, enormous. In the most common analysis method, parts of the meteorite are first almost completely dissolved in a strong acid. The small remaining residue is then slowly heated in a vacuum chamber, so that little by little the noble gases trapped in the material evaporate. These gases are then sorted by mass spectrometer by atomic weight and analyzed. display

As this process destroys parts of the valuable material the size of a euro coin, researchers have also developed other, gentler methods. The scientists from Mainz are best placed here with a system that uses a beam of electrically charged particles to extract atoms from the surface of the meteorite. These can then be examined in a spectrometer.

The results of this analysis enable a true pedigree of our cosmic ancestors: Individual granules can be assigned to a supernova - the spectacular end of a star that explodes in a huge explosion. The traces of the typical physico-chemical composition of the star that accompanies such an event still bear many of the dust particles today. Others come from a red giant, a star that, in the course of its development, has ballooned into a giant celestial body, throwing much material into space. Still other particles come from so-called novae, in which a star incorporates material from a neighbor.

Even the approximate age of these stars, which have long since disappeared, can be estimated by researchers. They exploit the fact that the particles on the way through the Milky Way now and then collide with hydrogen or helium ions, forming the isotope neon-21. The longer a dust particle traveled, until it finally became part of the solar nebula and thus of our later solar system, the more of this isotope was created. However, the exact determination is difficult: "Because of the small amounts of neon-21, this is only possible with jumbo granules, " explains Ulrich Ott in "bild der wissenschaft".

According to the results of the researchers, the particles were between 3 and 200 million years on the way, until they arrived in our 4.56 billion years ago just emerging solar system. This difference in travel time suggests that the particles are from different stars, which also had different ages. With this work on ancient stardust, researchers are now able to look back on the history of the Milky Way and draw conclusions about stars that have not shone for many billions of years.

ddp / - Ulrich Dewald

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