PRIM

How did our solar system form? Even though this question has motivated intensive research in recent decades, it is still posed and debated. PRIM tackles this question, and proposes new answers, based on ultra-high resolution mineral analysis of some of the most pristine material of our Solar System: the carbonaceous chondrites. These are pieces of the earliest small planets (planetesimals) that were forming our Solar System in the very first moments of its history. These small planets broke at a later time of their evolution, and some of their pieces, the carbonaceous chondrites, reached the Earth in the form of meteorites. We have gained access to ten of these primitive meteorites (Vigarano-like “CV” carbonaceous chondrites) that have been discovered on the Earth.
Using modern instruments such as a scanning electron microscope and an electron probe micro analyser, we analysed the secondary minerals that exist throughout the chondrites. Because those secondary minerals likely formed in their “parent body” (i.e. the small planet – now destroyed – from where these meteorites were extracted), they provide invaluable information on the planetesimals that were forming our Solar System. Our analyses revealed mineralogical assemblages whose formation required much higher temperatures than previously proposed. The thermodynamic modeling of the stability conditions for these mineralogical assemblages confirmed the high temperatures. Furthermore, the analyses revealed that the minerals formed from hot H₂-rich fluid phases, and not from low temperature precipitation in aqueous solutions as previously thought. Through the PRIM project, we have thus demonstrated that the parent bodies in our primitive Solar System were hot (fluids at T>350°C thus in gas form) and reduced (conditions allowing stability of both iron and magnetite). These are new important constraints to understand the original accretion scenario of our Solar System and the dynamics of the early Solar System. In particular, our new results call for the need to understand which accretional rates were able to produce such high temperatures.