Dust grains older than the Sun found on asteroid Ryugu

In 1950, Erwin Schrödingerone of the founders of the Quantum mechanicshaving worked both for the elucidation of the nature of life and for the appearance of matter in a model of relativistic cosmology, explained in one of the four public lectures entitled ” Science as a constituent element of Humanism ” that ” the isolated knowledge obtained by a group of specialists in a narrow field has in itself no value whatsoever; it has value only in the synthesis which unites it to all the rest of knowledge and only insofar as it really contributes, in this synthesis, to answering the question: Who are we? “.

We are indeed looking for our roots and our cosmic identity with space missions like that of the Japanese probe Hayabusa-2who was in orbit around the asteroid (162173) Ryugu from June 2018 to November 2019. She took samples there that have since been arrived on Earth and which are still being analyzed.

They therefore come from a member of the Apollo asteroid family, asteroids NEOs, and it is even among those that are potentially dangerous. It had been discovered in 1999 and it had quickly become clear that it belonged to the type C asteroids, that is to say similar to meteorites carbonaceous chondrites known on Earth.

Their chemical composition is therefore close to that of the material of the cloud molecular and dusty where the Solar system primitive, without the light and volatile elements like ice cream. It was therefore a target of choice for understanding the origin of the planets and the Sun and therefore the origin of the biosphere and the noosphere, so that Hayabusa-2 has provided us with much more than close-up images of asteroid (162173) Ryugu.

We can convince ourselves of this with the announcement made via a paper from an international team of researchers led by Jens Barosch and Larry Nittler of the Carnegie Institution for Science published in The Astrophysical Journal Letters.

The members of this team let it be known that they discovered in the samples brought back by Hayabusa-2 nothing less than presolar grains.

A key to the cycle of stars in the Milky Way

By this we mean solid materials that have condensed into grains, not in the protoplanetary disc of gas and dust in the process of cooling around the young Sun, approximately 4.5 to 4.6 billion years ago, but even before the birth of the Sun, in the atmospheres stellarstars existing before him and from which they were ejected at the end of their life to find themselves in the interstellar medium, then in the nebula protosolar origin of the solar system.

Remember that there is a real stellar cycle in the Milky Way which causes it to evolve chemically with an increasing enrichment of the interstellar medium in heavy elements. In this medium, molecular and dusty clouds, dense and cold, collapse gravitationally, destabilized under the effect of a pressurebe it density waves in the arms of our Galaxy or because of the shock wave from the explosion of a supernova.

As the clouds collapse, they fragment giving nurseries of stars, some of which will evolve very quickly by exploding into supernovae, injecting new heavy elements into the cloud where stellar formation continues. It is believed that the explosion of one of these stars, dubbed coatlicuecaused thecollapse of the protosolar cloud where our Sun was born. More generally, stars at the end of their life will return the matter that formed them to the interstellar medium, but with new elements, an environment in which, for the same reasons, new stars will be born.

This is what makes Jens Barosch say that, in the case of the finds in the Ryugu samples, ” different types of presolar grains come from different types of stars and stellar processes, which we can identify from their isotopic signatures. The possibility of identifying and studying these grains in the laboratory can help us to understand the phenomena astrophysics that shaped our Solar System, as well as other cosmic objects “.

Cosmochemists can indeed, with sophisticated microanalytical instruments, measure the abundances of various isotopic nuclei of an element differing in their number of neutrons and compare them with those measured in the chondrites carbons that crashed to Earth.

On this subject, and again in a press release from the Carnegie Institution for ScienceLarry Nittler explains that “ the compositions and abundance of presolar grains we found in the Ryugu samples are similar to what we have previously found in carbonaceous chondrites. This gives us a more complete picture of the formation processes of our Solar System that can inform models and future experiments on samples from Hayabusa2, as well as other meteorites. “.