The asteroid Ryugu has commonalities with rare meteorites considered to be the most primitive in the solar system. The first analyzes show perfect samples and even more unique than anything could be hoped for.
When the Hayabusa 2 probe left for the asteroid Ryugu to recover some pieces, hopes were high. The target, known to be an extremely primitive asteroid, was to tell us more about the beginnings of the solar system. Ultimately, the results exceeded expectations, according to a study published in the journal Science June 9, 2022.
The first analyzes of the samples collected in December 2020 had already shown that the sample was representative of the entire asteroid, which means that they are reliable and do not correspond to a zone a little apart from the star. Now, this new, more in-depth study reveals that Ryugu would actually be very close to the CI-type carbonaceous chondrite meteorites. For people who are not experts in meteorites, this is not very impressive at first sight, but for specialists, it is particularly interesting.
To reach this conclusion, it took several techniques for analyzing the samples collected by Hayabusa 2. The grains were passed through an electron microscope, X-rays, plasma mass spectrometry, a method capable of finding very weak amounts of metal, and surface ionization. Extremely fine analyzes that would have been unthinkable if the mission had been a simple observation without returning samples.
” It was a surprisetells Numerama one of the authors of the study, Laurette Piani, specialist in meteorites at the University of Lorraine in Nancy. There are so many kinds of chondrites that we absolutely did not expect it to be this particular type, which is very special. »
The best sample since 1864
Chondrites are so called because they are made up of chondrules, i.e. small silicate balls which represent up to 90% of their material. Carbonaceous chondrites are mixed with the matrix (sulfide, organic compounds, hydrated minerals, etc.) in very fine grains, and they are divided into different categories according to the amount of matrix present in their composition.
Type CI chondrites are a little different, because they have almost no chondrules, and up to 95% matrix. They are really sought after, because we have very few of them available. Their composition makes them extremely friable and rare are those that land on Earth without completely burning up in the atmosphere. Worse, if they ever touch the ground, they are quickly destroyed by the elements.
“The best way to get it, assures Laurette Piani, is to see one fall and go and pick it up right away! Which takes a lot of luck. ” Today, 17 kilograms of this type of meteorite have been discovered, which is quite a few, especially knowing that most come from a meteorite found in Orgueil, in the Tarn-et-Garonne, in 1864.
If the CI chondrites are so sought after, it is therefore for their rarity, but also because they are considered to be the most “perfect” in the solar system. They would have formed far from the Sun, in an area rich in water ice and organic matter, before migrating closer to the Earth. ” We suspected that Ryugu was born in the outer solar systemsays Laurette Piani, but the chances that it was this type of chondrite were low. »
These stars have a strong similarity with the solar nebula: they have the same elements and are for this reason used as a standard meter to determine if the other samples are enriched or depleted in certain elements. In other words, the CI chondrites are formed of the same elements that were present when the solar system was created.
Ryugu is perfect
This means that a good part of petrology, the study of the transformations of rocks, is based on the composition of these chondrites. And if Ryugu is one of them, that’s a big step forward. CI chondrites being rare and having been found a long time ago, analyzes concerning them can be unreliable. The means of analysis at the time were not the same as today, and they may have been altered over the years. However, Ryugu is perfect, his samples have been extremely well preserved since their collection to avoid any contamination of this type.
Laurette Piani adds: “ We found some differences between Ryugu and the other CI chondrites. In particular a slightly lower presence of water. It may mean that Ryugu was heated by the Sun and caused some water to evaporate. Or is it that the material found on Earth had been altered. »
The samples collected are too small in quantity to define a new standard meter for chondrites, but their study is valuable for learning more about the conditions that prevailed in the first million years of the solar system. Impossible for the moment to date Ryugu with precision, but the samples collected were formed barely 5 million years after the birth of the solar system. Future studies should further constrain the timeline to give us a more accurate idea of Ryugu’s age, but what is certain is that it is an essential witness to the beginnings of our world.