Unravelling the nature of an ice-rich body from the outer Solar System
Lead supervisor: Helen Williams, Department of Earth Sciences
Co-supervisor: Ross Findlay, Department of Earth Sciences
Research proposal
Context: The carbonaceous chondrite meteorites (CCs) are time capsules from the early Solar System that contain information pertaining to the accretion of the terrestrial planets and the evolution and distribution of water in the solar nebula [1]. Some of the original parent bodies — the asteroids from which these meteorites are sourced — originally bore an appreciable amount of water, accreted as a fraction of frozen water ice that subsequently melted due to the heat induced from radioactive decay [e.g., 2]. The water has since altered the mineralogy of these bodies, as sampled by meteorites, to include a high proportion of secondary minerals such as serpentines and carbonates.
Of particular interest are the CR, ‘Renazzo-type’ chondrites, which have long been thought to have formed in the outer Solar System at greater heliocentric distances to other CCs [3]. This is owed to their very elevated hydrogen isotopic composition in water and organic matter, which is equivalent to, or higher than that observed for comets [4]. Historically these meteorites have been rather rare; however, with an increase in the recovery of stones from hot deserts in North Africa, we are fortunate enough to possess a 51.9 g fragment of the CR chondrite Erg Chech 003, providing a large surface area to examine the petrographic relationships between its components.
Objectives: The intern will use Scanning Electron Microscopy (SEM) to petrographically characterise Erg Chech 003 by examining the texture and chemical composition of its constituent components that formed in the solar nebula. These include refractory calcium aluminium inclusions, chondrules (flash heated droplets of nebula dust), and the dusty, aqueously altered matrix that hold the specimen together. An additional focal part of the study will be to examine the polished blocks for any small, fine-grained clasts. These have been reported elsewhere and may be exogeneous fragments of comets [5]. Doing so will elucidate the nature and intensity of the aqueous alteration in Erg Chech 003, and by extension, its parent asteroid.
Methods: Following an initial settling / reading period (1 week) the intern will be trained how to sub sample the meteorite and make their own polished blocks by mounting them in resin followed by hand polishing (2 weeks). Following on will be a short SEM campaign to map and characterise the polished blocks using backscatter electron imaging and energy dispersive spectroscopy (2-4 sessions, 2 weeks). The data will then be processed offline to elucidate the degree of aqueous alteration (1 week), followed by interpretation and writing up the data into a report (2 weeks).
Expertise: Dr R. Findlay is a LCLU PDRA investigating aqueous alteration phenomena in carbonaceous chondrites, working with Professor Helen Williams.
Reading:
[1] Trigo-Rodríguez, J. M. et al., (2019). Space Science Reviews, 215, 1-27.
[2] Suttle, M., et al., (2021). Geochimica et Cosmochimica Acta, 299, 219-256.
[3] Schrader, D. L., et al., (2014) Earth and Planetary Science Letters, 407, 48-60.
[4] Bonal, L. et al., (2013). Geochimica et Cosmochimica Acta, 106, 111-133.
[5] Nittler, L. R. et al., (2019). Nature Astronomy, 3, 659-666.