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.