What is glowing here in the isolated vacuum chamber is a relic from the early days of our solar system. Because the small piece of rock comes from the asteroid Ryugu and is one of the samples that the Japanese space probe Hayabusa 2 collected from the asteroid and brought back to Earth in December 2020. The composition of the oxygen isotopes in one of these samples is being determined here.
Asteroids and comets are important contemporary witnesses from the beginnings of our solar system, because many of them formed together with the planets in the solar primordial cloud. In order to find out more about the composition of this environment and the processes taking place in it, scientists have so far mainly had to rely on meteorites. “Previously, we only had a handful of rocks for our analysis and they all came from meteorites that fell to Earth and were kept in museums for decades, changing their composition,” explains Nicolas Dauphas of the University of Chicago.
Samples from the asteroid Ryugu
But this changed with the Hayabusa 2 sample mission: In early 2019, the Japanese space probe took several samples from the surface of the asteroid Ryugu – a conspicuously angular chunk of a good 500 meters in size, whose origin and unusual features have so far been a mystery. Then, in December 2020, the spacecraft returned a total of five grams of asteroid material, which was parachuted down to Earth’s surface in a capsule.
“That’s a great success. The minimum goal of the mission was to collect around 0.1 grams,” explains Andreas Pack from the University of Göttingen. “In order to collect this sample, the probe traveled an elusive 5.4 billion kilometers.” Only a small number of laboratories worldwide received parts of the sample for initial analysis – the planetary researchers in Göttingen received a piece of 2.4 milligrams. Their isotope laboratory is one of the few laboratories in the world that can precisely analyze the rare O17 in addition to the oxygen isotopes O16 and O18.
On the trail of oxygen isotopes
Part of this sample is shown in this image during isotopic analysis of the oxygen atoms contained in the minerals. With this laser fluorination, the sample is heated with a laser beam and the oxygen is released from the minerals. Then the resulting gas is cleaned and analyzed for isotopes in a special mass spectrometer. “The analysis was very demanding, nothing could go wrong this time,” says Pack.
Analysis of the Hayabusa samples by various research teams has revealed that the asteroid Ryugu belongs to a particularly rare class of asteroids, the Ivuna-type carbonaceous chondrites. In terms of their chemical composition, these chunks are still very similar to the primordial solar cloud; they are, so to speak, a relic of the gases from which the sun was formed a good 4.5 billion years ago.
Cosmic Mud Ball
At the same time, the investigations also revealed that the asteroid material must have been soaked in water for the first five million years after the formation of the solar system. “You have to imagine a conglomerate of ice and dust that, under the influence of the radioactive decay of the radioactive elements inside, gradually melted and became a kind of mud ball,” explains Dauphas. Only then did the water evaporate again under the influence of the sun. This could also explain why Ryugu is so loosely put together and angular.
The analysis of the samples from the asteroid Ryugu is far from complete. Some of the precious sample material is also being kept untouched so that it can be examined in the future using even more modern methods – similar to what NASA did with the moon rock samples from the Apollo missions a good 50 years ago. “We are still learning new things from these old samples today because our measuring instruments and technologies have evolved,” explains Dauphas’ colleague Andrew Davis. “The same will be the case for the Ryugu samples.” (Science, 2022; doi:10.1126/science.abn7850)
Source: University of Chicago, Georg-August University of Göttingen
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