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Primitive meteorites: a new study explains why they are so rare on Earth

14 April 2025

While space missions such as OSIRIS-REx and Hayabusa2 bring back samples of carbon-rich asteroids, one question still puzzles scientists: why do we find so few so-called primitive meteorites on Earth? Primitive meteorites are essentially carbonaceous chondrites, i.e. fragments of asteroids that have preserved the original composition of the cloud of gas and dust that formed the Solar System. A study led by Patrick M. Shober (Observatoire de Paris - PSL) in collaboration with Curtin University and other institutions, published in Nature Astronomy, sheds new light on the subject.

Meteorites, witnesses to the Solar System’s past

A veritable celestial archive, meteorites are fragments of asteroids that enable us to trace the origins of the Solar System. Among them, carbonaceous chondrites occupy a special place. Originating from carbon-rich asteroids - such as Ryugu and Bennu, recently explored by the Hayabusa2 and OSIRIS-REx missions - these meteorites hold precious clues to the origin of water on Earth and the processes behind the first building blocks of life.

According to current models, a large majority of meteoroids - those objects before they enter the atmosphere - should be carbonaceous in nature. Indeed, most of them come from the asteroid belt, a region renowned for hosting carbon-rich bodies. It would therefore be logical to find a significant proportion of carbonaceous chondrites among the meteorites that have fallen to Earth.

Yet the study reveals that only around 4% of recovered meteorites are carbonaceous chondrites - a striking departure from traditional models..

When the Sun and Earth’s atmosphere act as a double filter

To resolve this paradox, the team of international researchers led by Patrick Shober, a researcher at LTE (Laboratoire Temps Espace) at Paris Observatory - PSL, analyzed almost 8,000 meteorite impacts and 500 potential meteorite falls, using data collected by 19 global networks of photographic surveillance cameras. These specialized systems record the trajectory of small rocky bodies as they enter the atmosphere.

Their work shows that primitive meteorites undergo a dual process of natural selection:

  • Thermal fragmentation even before coming into contact with the Earth. When a meteoroid passes close to the Sun, it undergoes intense thermal stress, which can weaken it and lead to its gradual disintegration.
  • Filtering by the Earth’s atmosphere. Among the meteoroids that penetrate the atmosphere, those with less resistance - and which, according to transport models, are predominantly carbonaceous in composition - burn up more easily, reducing their chances of reaching the ground as meteorites.

New insights into the dynamics of small Solar System bodies}

These results not only explain a rarity observed on Earth: they also open up new perspectives on the evolution of primitive Solar System materials and their role in planet formation.
By refining our understanding of the mechanisms that alter these bodies, notably the thermal cycle caused by their close passage to the Sun and space weathering, this study enables us to better interpret the samples brought back by space missions. It also sheds light on how similar processes might influence the population and composition of small bodies in other planetary and exoplanetary systems, providing us with a valuable frame of reference for interpreting remote observations.

This publication illustrates the place of Paris Observatory in contemporary astrophysics, as its President, Fabienne Casoli, points out:
“By studying meteorites and small bodies in the solar system, astronomers seek to better understand the history of the Earth and planets, as well as that of extrasolar planets. Observatoire de Paris - PSL continues to assert its leading role in these research themes, drawing on theory, numerical simulations and structuring programs such as FRIPON, SPHERE+, MICADO, PLATO, JUICE, MMX-MIRS and ENVISION.”

About Observatoire de Paris - PSL

Founded in 1667, the Observatoire de Paris - PSL has been a center of innovation and discovery in astronomy for nearly 360 years. With 750 researchers and teacher-researchers, engineers, technicians and administrative staff, the establishment conducts research on its 3 campuses - Paris, Meudon and Nançay - in astrophysics, physics, engineering and the metrology of time and space. Its work combines theory, numerics, experimentation, ground-based and space-based observations, and instrumental development. Observatoire de Paris - PSL is responsible for the production of French legal time and ephemerides for the Sun, Moon and solar system bodies, which are entrusted to it by decree. It operates state-of-the-art radio telescopes at its Nançay site. It offers academic training (Masters, PhD), training for the general public and teachers, and class sponsorship. It is a founding member of the Université Paris Sciences et Lettres, where it runs the Astrophysics graduate program.

Différences dans les distributions orbitales entre les impacteurs terrestres et les impacteurs produisant des météorites.
Differences in orbital distributions between terrestrial and meteorite-producing impactors
Heat maps of the relative differences between the normalized densities of all terrestrial impactors (masses greater than 10 g) and those of meteorite-falling impactors (masses greater than 1 g) across various orbital parameter ranges. Red regions indicate orbits where meteorite falls are more frequent relative to the total impactor population; blue regions, a relative deficit of meteorite falls. Black contours indicate statistically significant differences at the 3σ level (chi-square test); all other regions are significant at the 2σ level. The coloured lines show the expected evolution of the perihelion under the effect of the Kozai-Lidov resonance (for a semi-major axis of 2.5 AU), which can exchange inclination (i) for eccentricity (e), thus explaining why an excess of meteorite-producing impacts is observed for high inclinations and perihelion distances close to 1 AU.
Crédit : Patrick M. Shober

Collaboration

 Patrick M. Shober - LTE, Observatoire de Paris-PSL, Sorbonne Université, Université de Lille, LNE, CNRS
 Hadrien A.R. Devillepoix - Space Science and Technology Centre, Curtin University ; International Centre for Radio Astronomy Research, Curtin University
 Jérémie Vaubaillon - LTE, Observatoire de Paris-PSL, Sorbonne University, Université de Lille, LNE, CNRS
 Simon Anghel - LTE, Observatoire de Paris-PSL, Sorbonne Université, Université de Lille, LNE, CNRS ; Astronomical Institute of the Romanian Academy
 Sophie E. Deam - Space Science and Technology Centre, Curtin University; International Centre for Radio Astronomy Research, Curtin University
 Eleanor K. Sansom - International Centre for Radio Astronomy Research, Curtin University ; Space Science and Technology Centre, Curtin University
 François Colas - LTE, Observatoire de Paris-PSL, Sorbonne Université, Université de Lille, LNE, CNRS
 Brigitte Zanda - Institut de Minéralogie, Physique des Matériaux et Cosmochimie, Muséum National d’Histoire Naturelle, CNRS ; LTE, Observatoire de Paris-PSL, Sorbonne Université, Université de Lille, LNE, CNRS
 Pierre Vernazza - Laboratoire d’Astrophysique de Marseille, Aix-Marseille Université, CNRS, CNES, LAM, Institut Origines
 Phil Bland - Space Science and Technology Centre, Curtin University

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