Aims: This project will explore the dynamics and composition of our Solar System during its tumultuous birth ~4.5 billion years ago by studying fragments of highly primitive asteroids that are preserved as xenoliths in meteorites. The xenoliths were broken from their parent asteroids during catastrophic collisions, then moved through the protoplanetary disk to eventually be incorporated into other asteroids – it is pieces of these secondary asteroids that have fallen to Earth as meteorites. The xenoliths that they contain therefore preserve a record of asteroids that ‘lived fast and died young’ and as such can provide unique insights into the origin of our Solar System.
Context: Thousands of meteorites are available for study, the majority of which are from asteroids that orbit the Sun between Mars and Jupiter. The most primitive meteorites are the carbonaceous chondrites, which are derived from C-complex asteroids that populate the cold and dark outer reaches of the asteroid belt. One such meteorite fell in Winchcombe, Gloucestershire, in 2021 (O’Brien et al. 2022). The carbonaceous chondrites are of great interest because they contain primordial water and organic matter. Those meteorites that fell to Earth early in its history may therefore have bought with them a host of bio-essential compounds that eventually enabled life to evolve.
Despite their importance, carbonaceous chondrite meteorites are inherently limited in the information that can provide about early Solar System evolution. They are derived from the present-day population of asteroids and even then, meteorites can only be delivered to Earth from certain parts of the asteroid belt. In addition, only sufficiently tough rocks can survive the high pressures and temperatures of passage through Earth’s atmosphere. By contrast, xenoliths are fragments of asteroids that formed whilst the Solar System was very young but may have been long since destroyed, and they are protected from the rigours of atmospheric entry by their enclosing meteorite so that even the most fragile lithologies can survive (Nittler et al. 2019).
Objectives: Xenoliths are very abundant in some meteorites belonging to the CM group of carbonaceous chondrites (e.g., Lindgren et al. 2013). They can preserve a rich record of the geological history of their parent asteroids through assemblages of minerals including carbonates and phyllosilicates, and textures including mineral veins and compactional petrofabrics. Using these and other features of the xenoliths we will seek to understand how their parent asteroids evolved including evidence for the presence and flow of liquid water, and the extent to which they were deformed by impacts prior to breaking apart. During their transfer between asteroids the xenoliths have accreted finer grained material that was also free-floating in the protoplanetary disk, and bought it with them into the secondary asteroid. The xenoliths thus also serve as a form of ‘witness plate’, collecting and sampling a variety of materials that were present in the early protoplanetary disk.
Techniques, training and career prospects: The student will be trained to characterise the xenoliths and their host meteorites using an array of conventional tools (e.g., scanning electron microscopy, Raman spectroscopy, electron probe microanalysis, secondary ion mass spectrometry, transmission electron microscopy) and emerging analytical techniques (i.e., X-ray tomography, atom probe tomography and transmission Kikuchi diffraction). They will become part of a lively team of planetary scientists in Glasgow and will work within a vibrant research community in the UK and internationally. The student will have ample opportunity to travel widely in the UK and internationally in order to undertake research and present results. The student will gain subject specific and generic skills that can lead to employment in areas such as resource exploration, environmental management and space science.
Applicants: The project is suitable for a graduate with a good honours degree in Geology or Earth Science with an interest in Planetary Science. There are two routes to apply for this PhD project.
References
Lindgren, P. et al. (2013) Clasts in the CM2 carbonaceous chondrite Lonewolf Nunataks 94101: Evidence for aqueous alteration prior to complex mixing. Meteoritics & Planetary Science 48, 1074-1090.
Nittler, L. R. Et al. (2019) A cometary building block in a primitive asteroidal meteorite. Nature Astronomy 3, 659–666.
O'Brien, A. C. et al. (2022) The Winchcombe Meteorite: one year on. Astronomy and Geophysics 63(1), 1.21-1.23.
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