The solar system’s first organics - investigating the role of coatings on pristine presolar grains

Murchison meteorite

The Murchison meteorite © The Trustees of the Natural History Museum, London

The solar system was born 4.6 billion years ago with the collapse of a cloud of dust and gas synthesised in the atmospheres of ancient stars. A small fraction of this 'presolar' dust survived the formation of the solar system and can be found in primitive meteorites.

Identified by isotopic compositions that vary by orders-of-magnitude from solar values, presolar grains of SiC, graphite, oxides and silicates can be used to trace the physical and chemical conditions in stellar environments, the interstellar medium (ISM) and the early proto-planetary disk [1]

Presolar SiC grains were first extracted from meteorites using harsh acid dissolution techniques [2]. However, evidence that these treatments may alter grain surfaces led to the development of non-acid isolation methods to obtain “pristine” SiC [3, 4].

Early studies showed that many of the pristine grains have thin (<100 nm), possibly organic, amorphous coatings never previously observed on acid extracted grains [3]. These coatings could be remnants of organic mantles that formed when simple ices (e.g. H2O, CO and CO2) deposited onto grain surfaces were processed via photolysis and sublimation in the cold ISM or outer regions of the proto-planetary disk [5].

The nature and origin of the coatings on pristine presolar SiC grains remains unknown but they potentially offer a crucial link between organic materials observed in interstellar space and those present at the start of the solar system. 

This project will investigate coatings on pristine presolar SiC grains using a combination of state-of-the-art imaging, spectroscopic and isotopic techniques

Grains will be identified in both existing and new separations prepared from primitive meteorites without acids using a scanning electron microscope and X-ray analysis (SEM-EDX).

The chemistry of the coatings will then be characterised using Raman, nano-infrared (IR) and C, N and O X-ray absorption near-edge structure (XANES) spectroscopy at Diamond Light Source (DLS), the UK’s national synchrotron facility. The relationship between coatings and grain interiors will be explored with international collaborators using transmission electron microscopy (TEM) and isotopic compositions will be determined using secondary ion mass spectrometry (NanoSIMS).

Results will be compared to the properties of other extraterrestrial materials and astronomical observations of star-forming regions and the ISM to provide unique new insights into the evolution of organic matter in space. 

This project will utilise the world-class meteorite collection and analytical facilities available to the Planetary Materials Group at the Natural History Museum, London, and the Planetary and Space Science Group at the Open University. The project would suit an enthusiastic individual with a keen interest and strong background (BSc/MSc) in Earth/Planetary science, Physics/Astronomy or Chemistry, and demonstrable experience and in advanced laboratory analytical experiments. 

Eligibility

To be classed as a home student, candidates must meet the following criteria:

  • Be a UK National (meeting residency requirements), or
  • Have settled status, or
  • Have pre-settled status (meeting residency requirements), or  
  • Have indefinite leave to remain or enter  

 If a candidate does not meet the criteria above, they would be classed as an International student.

Further guidance on UKRI Eligibility Criteria can be found on the UKRI website

How to apply

Please send the following documents to Anna Hutson (postgradoffice@nhm.ac.uk)

  • Curriculum vitae
  • Covering letter outlining your interest in the PhD project, relevant skills training, experience and qualifications, and a statement of how this PhD project fits your career development plans.
  • Transcripts of undergraduate and Masters degree results.
  • Two academic references including (if applicable) Masters project supervisor.
The lifecycle of presolar grains

The lifecycle of presolar grains (left), and examples of coated presolar SiC grains from the Murchison meteorite (right, image from [3]).

Apply for this project

This is a collaborative project between the Natural History Museum and the Open University funded by the Science and Technology Facilities Council (STFC).

Read the eligibility criteria and application guidance below, then send your application to postgradoffice@nhm.ac.uk.

Application deadline: 29 January 2021

Any questions?

Natural History Museum

Main supervisor: Dr Ashley King

Supervisors

Natural History Museum

Dr Ashley King

Open University

Dr Ian Franchi

References

[1] Davis AM (2011) Stardust in meteorites. PNAS 108:19142

[2] Amari et al. (1994) Interstellar grains in meteorites: I. Isolation of SiC, graphite and diamond; size distributions of SiC and graphite. GCA 58:459

[3] Bernatowicz et al. (2003) Pristine presolar silicon carbide. GCA 67:4679

[4] Tizard et al. (2005) The gentle separation of presolar SiC grains from meteorites. M&PS 40:335

[5] Ehrenfreund P and Charnley SB (2000) Organic Molecules in the Interstellar Medium, Comets, and Meteorites: A Voyage from Dark Clouds to the Early Earth. Ann. Rev. Astron. Astrophys. 38:427

We welcome applications from everyone

We offer a stimulating and professional environment in which to work. We look for staff who can work according to our values: diversity, creativity, connection and evidence-based thinking.