Planetary Origins and Development (OxPOD)

Based on radioactive dating of the oldest particles in meteorites, the solar system formed from a flattened disk of gas and dust about 4.57 billion years ago. With the sun at the centre going through its earliest, violent stages of development, gases such as hydrogen, helium, water ammonia and methane were swept to the outermost parts, beyond the asteroid belt, where they were condensed into the giant planets Jupiter, Saturn, Uranus and Neptune. The inner solar system consisted predominantly of dust and this dust gradually clumped together over 10's of thousands of years and grew into a large number of bodies of 10-100 km in size. Over periods of 3 to 30 million years these small bodies collided and grew into the inner planets, Mercury, Venus, Earth and Mars, leaving the smaller asteroids of the asteroid belt as remnants of the period before the planets grew.

This project is aimed at the understanding of some of the most important processes which took place on small asteroids and during growth of the planets using a combination of studies of meteorites and experiments aimed at simulating conditions on growing planets during the earliest history of the solar system. We are particularly interested in how the inner planets acquired their inventories of the so-called "moderately volatile elements" such as sulphur, chlorine, zinc and lead, and how these and other volatile elements, notably the noble gases Helium, Neon, Argon, Krypton and Xenon, are degassed to the atmosphere and recycled to the planet's interior. We are also building the capacity to simulate experimentally the conditions deep within the outer solar system planets Uranus and Neptune, which are believed to contain significant amount of methane. Individually our 5 inter-related projects may be summarised as follows:

A. Addresses the question of how the planets of the inner solar system obtained their current concentrations of moderately volatile non-metals such as sulphur and chlorine and asks if the mechanisms of acquisition are different from those in which the volatile metals such as zinc, lead antimony and copper were acquired. This involves melting rocks containing these elements at temperatures of about 1300oC and determining the rates at which the different elements are lost to the atmosphere.

B. What are the physical and chemical pathways by which sulphur is cycled through Io's interior? Io, a moon of Jupiter, is the most volcanically active body in the solar system and its atmosphere is being continually replenished by sulphur-rich gases emitted by volcanoes. This project uses computer modelling to address the ways in which sulphur is emitted to the atmosphere, condensed on the surface and then recycled to the interior.

C. How has hydration of the martian surface led to recycling of volatiles including water, the noble gases, chlorine, bromine and iodine? These gases become fixed on Mars' surface by being locked into a common mineral, amphibole. The aim of this project is to determine, by high pressure experiment, the extents to which these elements can be trapped in amphibole and recycled to the martian interior.

D. How did addition of water to carbon-rich asteroids lead to the growth of magnetite? A large proportion of carbonaceous meteorites have undergone aqueous alteration on their parent bodies and magnetite is an important clue to the processes involved. This project is aimed at experimentally simulating in the laboratory the transformation processes which lead to magnetite of the types observed.

E. What are the properties of methane and water under the extreme pressure and temperature conditions in the interiors of Uranus and Neptune? This project is aimed at determining which compounds of methane and water are stable in the interiors of these giant planets and providing data to enable modelling of the planetary properties.

Geochemistry is now the single biggest discipline within Earth System Sciences, providing many of the critical data and constraints planetary scientists are using to interpret the latest observations of our solar system and of exoplanets. The potential to apply our geochemical knowledge is considerable. Our unique capabilities combining observational data with experimental tests and high-precision geochemical analysis, have resulted in links with a number of areas relevant to the wider UK science strategy. Among these are the life sciences, where our ability to measure minute changes in elemental and isotopic compositions is being explored to detect early-stage disease (single-cell/small particle analysis in collaboration with the MRC Weatherall Institute for Molecular Medicine, Prof. Drakesmith and Perkin Elmer). Another example is in chemical engineering where our modelling capabilities have led to new discoveries of globally important commercial helium resources (Helium One). Our expertise in high pressure experimentation has a world-wide impact, demonstrated by the construction of a simple, inexpensive piston-cylinder apparatus brought to Oxford and designed by Bernard Wood. The workshop in Oxford has so far constructed and sold 9 of these apparatuses to Universities in Australia, Canada, USA, France, Germany and Ireland.
The questions posed in this proposal are of fundamental importance to a range of academic fields, not least those involved with planetary observation, formation and evolution. The ability to observe exoplanet chemistry and planetary nebulas is a new but rapidly expanding field. The interpretations are, however, based on fundamental geochemical data which are largely founded on Earth materials, or, in the case of element volatility during the accretion phase, poorly constrained. By exploring the chemistry of silicates sulphides and gases of non-terrestrial compositions, this proposal will significantly expand our understanding of materials pertinent to both solar system bodies, including Mars, Io and the gas giants, and exosolar planets of more exotic sizes and compositions. To facilitate a more rapid flow of results with the astronomy and planetary exploration community, we have formed strong links with local colleagues in physics and astronomy (e.g. OxfordPlanets.uk).
Our results will also be relevant to industry gaseous emissions which occur during smelting operations and we consider that presenting papers at appropriate conferences attended by industry representatives (e.g CALPHAD-Boston 2021) and the international mineral processing conference (Cape Town 2020) are potential venues for us to interact more formally with industry. We will work with Oxford's well-resourced and effective Technology Transfer Office, Oxford University Innovation, to also ensure that emerging opportunities for knowledge exchange are actioned throughout the tenure of the consolidated grant and beyond.
The 'big questions' nature of our science - the formation of the planets and the processes that led to the Earth's habitable and Mars' inhospitable surface - are a proven outreach 'hook'. These topics are an excellent entry to engage with communities that may otherwise not connect with 'traditional' outreach activities. All members of this application have delivered an extensive variety of outreach activities, ranging from local talks to engage the general public, to school visits across the U.K, web-casts, public talks (e.g. Edinburgh Science Festival, 2019 - Wade, Faculty outreach lead) and international media. The University of Oxford has a highly effective press office. The Oxford Science Blog has a wide reach (including social media) and aims to communicate current research outputs by Oxford researchers to the public.