Before Earth, there were asteroids ☄️

A study led by researchers from the Institut de Physique du Globe de Paris (IPGP), published in the journal Science Advances on January 8, 2025, reveals a breakthrough in understanding the early stages of the solar system's formation.


By studying the oldest known differentiated meteorite, Erg Chech 002 (EC 002), they established a new benchmark for the initial abundance of a radioactive isotope, while revealing the early onset of metal core formation processes in asteroids.

The isotope ⁶⁰Fe, with a half-life of 2.62 million years, no longer exists in the solar system. However, its decay product, still present in samples as ⁶⁰Ni, allows us to infer its initial abundance, a crucial parameter for dating the formation of metal cores in planetesimals — these precursor bodies of planets. Until now, estimates of the initial abundance of ⁶⁰Fe varied widely, ranging from 10⁻⁹ to 10⁻⁶, making its use as a cosmic chronometer uncertain.


In this study, researchers developed a new method for analyzing nickel isotopes, combining unmatched sensitivity and precision through MC-ICP-MS mass spectrometry. This approach allowed them to precisely define an initial ⁶⁰Fe/⁵⁶Fe ratio of (7.71 ± 0.47) × 10⁻⁹, a value five times more accurate than previous estimates.

This result, now recommended as a standard reference, confirms that the radioactive isotope ⁶⁰Fe originated from the interstellar medium, ruling out the hypothesis of a late injection by supernovae into the early solar system.

Asteroid cores formed very early

Using ⁶⁰Fe-⁶⁰Ni chronologies, researchers also dated the formation of metal cores in several asteroids:
- EC 002: differentiated metal at only ~0.82 million years after the solar system's formation.
- Asteroid Vesta-4: core formation at ~0.95 million years.
- Parent body of angrites: formation at ~2.27 million years.

These results show that asteroid differentiation — i.e., their transformation into bodies with distinct cores, mantles, and crusts — occurred extremely early, within the first two million years after the solar system's birth. Most meteorite fragments we have today thus originate from these rapidly formed bodies.

An unexpected thermal and volcanic diversity

The study also reveals the stages of the thermal evolution of EC 002's parent planet. After the stabilization of a chondritic crust atop a magma ocean, metal segregation occurred at moderate temperatures (1000°C to 1200°C), followed by an intense silicate melting event at 1.62 million years.

These observations highlight the diversity of volcanic processes and evolutionary trajectories of early planetesimals.

Reference:
Fang, Moynier, Chaussidon, Limare, Majhatadze, Villeneuve.
The initial solar system abundance of ⁶⁰Fe and early core formation of the first asteroids.
Science Advances.