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Stardust to asteroids: Unravelling the formation and earliest evolution of a habitable solar system

Final Report Summary - STARDUST2ASTEROIDS (Stardust to asteroids: Unravelling the formation and earliest evolution of a habitable solar system)

The main objective of the STARDUST2ASTEROID project is to investigate the timescales and processes – including the role of supernovas – leading to the formation of the solar system by measurement of isotopic variations in meteorites. To achieve our objectives, we integrate long-lived and short-lived radioisotope chronometers with the presence/absence of nucleosynthetic anomalies in various meteorites and meteoritic components. This allows us to insights into the formation and earliest evolution of the solar system and, hence, the initial conditions required for the formation of habitable worlds. During the grant period, we have published 43 papers in top-tier peer reviewed journals. We briefly outline below some of the major discoveries.

Reporting in Nature, we show that the primordial crust of Mars solidified extremely rapidly, no later than 20 Myr after formation of our Sun. This result completely revises the formation timeline of the planet, including its potential early habitability. Indeed, our data require that conditions amiable to life existed on Mars 100 Myr earlier than on Earth, allowing life in our solar system to have first evolved on Mars. This work was promoted on the front page and highlighted in a News and Views feature.

Publishing in Nature, we reported the discovery of a relationship between the mass of rocky planets from the inner solar system and their calcium isotope composition. This observation provides empirical evidence supporting a new planet formation paradigm known as chondrule accretion, which requires that accretion of the rocky planets occurred within the 5 Myr lifetime of the solar disk. These results have transformed our understanding of planet formation processes and timescales. This work was highlighted in a News and Views.

The most abundant constituent of primitive meteorites are chondrules, i.e. mm-sized solids that were free-floating in the protoplanetary disk and fuelled the growth of planets. The current paradigm is that these objects formed 2-3 Myr after the birth of our Sun. Reporting in Science Advances, we defined an absolute and assumption-free chronology of chondrules, showing that their primary production was restricted to the first million years after the formation of the Sun and that these existing chondrules were recycled for the lifetime of the protoplanetary disk. This abundance of chondrules at earliest times provides the material required to drive the rapid formation of planets.

The most pristine objects in our solar system are comets, which preserve a record of the original material that assembled to form planets, including prebiotic molecules. Reporting in PNAS, we show that a class of chondrites, the metal-rich carbonaceous chondrites, have compositions requiring their formation in the outermost solar system where cometary objects exist. Thus, these meteorites provide a direct window into the origin of the solar system, including the building block of life on Earth.

The abundance of metals (metallicity) in stars provides a fossil record of the chemical composition of the initial protoplanetary disk. Reporting in Nature, we show that exoplanets can be categorized into three populations defined by distinct host star metallicities, including a new class of planets that we dubbed gasdwarfs. This recognizes for the first time that disk metallicity determines the structure of planetary systems.