Building asteroids from piles of rubble – insights from CM carbonaceous chondrite xenoliths

Spacecraft from NASA and the Japan Aerospace Exploration Agency (JAXA) are currently exploring the near-Earth asteroids Bennu and Ryugu. Both bodies are spectroscopically linked to the carbonaceous chondrites, with the Mighei-like (CM) meteorites being a particularly good analogue for Bennu. These asteroids are ‘rubble-piles’, meaning that they are composed of fragments of earlier bodies that are weakly bound together, giving the asteroid a low bulk density. Recent high-resolution images have shown that the surfaces of Bennu and Ryugu are littered with angular rock fragments of a wide size range, and probably of different compositions. The similarities with the CM chondrites are striking - many of them spent at least some of their history very close to the surface of their parent asteroid, and most are breccias. Some of the breccia clasts are CM carbonaceous chondrite lithologies whereas others are allied to different meteorite groups (i.e., xenoliths). The focus of this project is on understanding the origin and history xenoliths in CM carbonaceous chondrites, which will help greatly in interpreting samples that will soon be returned to Earth from Ryugu and Bennu.

Project plan: This project will be the first systematic study of xenoliths in the CM chondrites. Meteorite samples will be obtained from museum collections. Xenoliths will be located and identified by non-destructive 3D imaging using X-ray tomography, and by characterising samples in thin section using scanning electron microscopy. The mineralogy and chemical composition of identified xenoliths will be determined by techniques including electron backscatter diffraction, X-ray microanalysis, X-ray diffraction, atom probe tomography and oxygen isotopic analysis. This work will be done in Glasgow, at collaborating laboratories, and national science facilities (e.g., Diamond light source). The end-result of the project will be a new understanding of the dynamics of transfer of asteroidal material, and the mechanisms and timing of incorporation of this material into carbonaceous chondrite parent asteroids.

Training: The student will become part of a lively team of planetary scientists in Glasgow and will be trained in mineralogy, petrology and planetary science in addition to science communication. The student will also work within a vibrant research community in the UK and internationally, and will have the opportunity to travel widely in order to undertake research and present results at conferences.