Isotopic Studies of Early Planetesimals and Planetary Embryos

Lead Research Organisation: University of Oxford
Department Name: Earth Sciences


The research in this proposal tries to answer big questions about why we are here. Not just...why you and I are here. Not just...why humans are here. Not just...why animals evolved. Not even...why life started. But...why we have an Earth and Solar System at all. The best way to describe what this research will achieve is to list some good questions and then to explain what it is we are doing to try and figure out the answers. Question 1. What would it be like to roam around the Sun in a spaceship when the planets were being made? It would have been a lot more complicated than today because we are sure the planets formed from a swirling disk of gas and dust. We do not know how material moved around and mixed nor where many early objects came from. We can find out from precise measurements of small differences in the kinds of atoms present. These act as a kind of signature of bits of the disk and allow us to track motions rather like a detective uses fingerprints to trace a robber. Question 2. How were the planets created? We think that in this dusty disk the rock and debris somehow stuck together into tiny planets, which then dragged more rock onto them by gravity. Nobody knows exactly how this gets started. It is one of the biggest problems in planetary science. Gravity does not do much until an object is about the size of a small village. How to make things the size of a car or even a football pitch is harder to understand. We could test some theories if we knew how fast it happened. We will try and answer this by dating some of the meteorites that formed from early proto-planets. Question 3. Why do we have iron cores in terrestrial planets? We think the Earth's core formed from an ocean of molten rock created from the incredible heat resulting from accretion events like the Moon-forming Giant Impact. However, we do not understand how metal first formed and segregated from the first proto-planets. What provided the heat? It could have been radioactive energy or impacts. By finding out when melting and metal segregation occurred we can determine how it happened because radioactive isotopes and radiogenic heat production decay with time.


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Armytage R (2011) Silicon isotopes in meteorites and planetary core formation in Geochimica et Cosmochimica Acta

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Armytage R. M. G. (2009) Silicon isotopes in achondrites and the light element in Earth's core in GEOCHIMICA ET COSMOCHIMICA ACTA

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Fehr Manuela A. (2009) Tellurium isotope compositions of calcium-aluminum-rich inclusions in METEORITICS & PLANETARY SCIENCE

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Halliday AN (2009) Geophysics. How did Earth accrete? in Science (New York, N.Y.)

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Halliday AN (2012) Planetary science. The origin of the Moon. in Science (New York, N.Y.)

Description We tackled a controversial problem about the light element that exists in Earth's core. It was shown 60 years ago that the density of the core was too low for it to be made of just iron and nickel. Following our earlier work we conducted the most detailed studies to date of the silicon isotope composition of the Earth and meteorites and confirmed that the silicate Earth's silicon is isotopically heavy, consistent with it being fractionated by core formation. That is silicon is a light element in the core.

We also developed and worked on vanadium isotopes and showed that there is also a vanadium isotopic difference between the silicate Earth and meteorites but that this cannot be explained by core formation because the effect is too large based on experimental work.

We also developed tungsten isotopes. This was initially with a focus on radiogenic tungsten. This was unsuccessful but with a change in the team we switched to stable tungsten isotopes (after this award). This is a completely new technique.
Exploitation Route The developments of silicon and vanadium have been part of a broader set of developments of isotopic methods used by others world wide but mainly for geochemistry
Sectors Environment

Description Public outreach - giving talks about the origin of the Earth and Moon
First Year Of Impact 2010
Impact Types Societal