NAME: Nicci Potts
BACKGROUND: I’m a postdoctoral researcher in the School of GeoSciences, University of Edinburgh, United Kingdom (UK). I started out with a BSc in Geological Sciences, University of Leeds, and then I did a MSc in Geochemistry also at Leeds. After a short break spent travelling, I did my PhD at the Open University, UK and the Vrije Universiteit Amsterdam, Netherlands. My research is focused on understanding the behaviour of volatiles in the early inner Solar System, using the Moon as a proxy for how volatile elements might be incorporated into solidifying bodies. I use experimental petrology techniques to recreate high temperature and high pressure conditions and combine my experimental results with analysis of extra-terrestrial samples.
PROJECT TITLE: Constraining the volatile inventory of the lunar interior
LOCATION: University of Edinburgh
AREA OF EXPERTISE: Experimental petrology, thermodynamics, mineralogy, lunar petrology, volatile elements
What’s the purpose of your project?
My ultimate aim is to understand if volatile elements (water, chlorine, flourine, sulphur, etc.) are present during planet formation and evolution. This is because volatile elements have a big impact on key processes and so would change the parameters we use in models of Earth and exoplanet formation. The current thinking is that most volatile elements would be degassed to space during planet formation as temperatures would be so hot but geochemical signatures don’t necessarily confirm this. I’m using the Moon as a proxy for planet formation, as we know if formed from a hot process, it’s geochemically linked to the Earth. We have samples from deep within the Moon, and its history has been dull enough to prevent anything interfering with primordial signatures.
How are you setting up and testing your project?
I’ve made a replica lunar mantle composition and doped it with various amounts of water, flourine, chlorine, and sulphur. I then use a piston cylinder apparatus to recreate the conditions expected for lunar mantle formation, so temperatures between 1150 – 1350 degrees centigrade and pressure between 1 – 3 GPa. To achieve such high temperatures and pressures, my sample capsules have to be pretty small (~8 mm x 4 mm). Each experiment grows some mix of olivine and pyroxenes with surrounding melt quenched to a glass. I do quantitative analysis on a CAMECA 4f ion microprobe and a CAMECA 1270 ion microprobe for volatile elements. As the concentrations in the phases are so low (<10 ppm), I need high precision measurements which the ion microprobe allows at small beam sizes. With measurements of volatiles in melt and surrounding phases, I can calculate partition coefficients. These values can then be applied to natural samples to back-calculate volatile contents in the melt knowing only abundance in the natural phase. Most importantly, I can calculate how much volatile material COULD be stored in the lunar mantle to gain an idea of the storage capacity of planetary interiors.
Any results yet?
Not really. Experimental petrology can be challenging at times. We’ve had some ongoing issues which have delayed my experiments. Also combining ion microprobe and experiments is tricky, as I need to grow sizable grains (> 50 um x 50 um) for analysis which is actually difficult in my system. I’ll be doing some tests on the instrument to see what the trade-off between beam size and background contamination is so that I may be able to measure smaller grains (~20 um x 20 um). I expect very low concentrations in my olivine and pyroxene grains.
What has been the most interesting or challenging?
Issues in the lab have meant my bedtime reading has been ‘how transformers work’ or ‘what does a thyristor do?’ … information I never thought I would need to know previously. I really enjoy the practical side to science (i.e. I like getting my hands dirty) and thrive on the challenges lab work throws at you. On reflection, I would have done instrument testing much earlier – rather than my multiple attempts to grow bigger grains – but I’m constantly evolving in my role and getting a lot of new skills out of the project!
How will this project help society?
If we can understand whether volatile elements were present during planet formation/evolution then it will go towards answering some of our questions about how life evolved on Earth – and maybe why Earth is unique with liquid water on the surface and evolved life. This is also important for our upcoming missions to study exoplanets. We are searching for ‘Earth-like’ planets that are ‘habitable,’ yet we don’t know what makes Earth Earth-like or habitable! Also, as we can’t see exoplanets, we make assumptions about their mass based on size – the abundance of volatile elements in a planet during formation could change this, so it’s important to know whether we have to consider volatiles in planet models!