The primordial dust of our world

It’s a vertiginous moment: for the first time, we see the primordial matter of our world. We see what the dust that floated in our little corner of the Universe looked like, long before it came together to give birth to the Sun, 4.5 billion years ago, then to the Earth and the others planets.

This dust was collected in 2019 from an asteroid, Ryugu, located several hundred million kilometers from here. The 5.4 grams recovered by the Hayabusa2 probe, from the Japanese space agency, were brought back to Earth at the end of 2020. And it was not until the joint work of several hundred astrochemists to know its composition, which comes from be published.

The researchers are relieved: yes, as expected, these particularly fragile grains of matter have been very delicately preserved in their original state by the asteroid. A few rare types of meteorites that have fallen to Earth have already brought us such presolar remains. But it was difficult to know if these materials had not undergone alterations during their fall. Here, the material is in its original, raw state, protected from chemical alterations and the rays of the Sun by the frozen asteroid, born at the edge of our system.

Graphites, oxides, silicates, organic compounds… The 57 presolar grains identified are distinguished from other materials by their very anomalous isotopic compositions, that is to say by the singular number of neutrons present in their atoms, in particular those of oxygen and carbon. And their analysis makes it possible to reconstruct the antediluvian astrophysical phenomena that have shaped our world.

Here, we see a grain of dust born from a super-nova: it is the pure trace of the explosion of a large star, which enriched the interstellar space, then the nebula at the origin of the Solar System . There, two more oxygen-rich dust grains are the remnants of smaller stars.

The in-depth analysis of these grains and their abundance has only just begun. This is a unique opportunity to revive these stars, long gone. With these specks of dust, the prehistory of our world begins to be written. The history of the world before.