Planetary Origins and Development

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Scientists can now detect Earth-sized planets orbiting other stars far away in our Milky Way galaxy. Yet, many basic aspects of how planets first form, then develop and function are unknown or surprisingly uncertain. The research in this proposal will address some of the questions to which scientists seek answers in this fascinating area. The subjects in which we work are called isotope cosmochemistry, petrology, rock physics and low temperature geochemistry. Four lead investigators with these different backgrounds will work together to address five big questions. 1. What processes generated the atoms from which our Solar System was built? Hydrogen and helium are mainly the product of the Big Bang 13.8 billion years ago. But what about all the heavier elements like calcium, titanium, chromium, nickel, zirconium, molybdenum or palladium? Since the 1950s there have been well accepted theories for how these heavier elements were synthesised in large stars. Now there is evidence these theories may be wrong. We will measure the proportions of the isotopes of these elements in some of the oldest material in the Solar System to test the new theories. 2. What processes govern the amount of volatile elements like tin in the terrestrial planets? We will perform experiments using a recently-built furnace to determine the relative losses and isotopic fractionation of such moderately volatile elements from molten asteroidal and planetary bodies. We will evaluate whether very early processes in the circumstellar disk were responsible or whether there were losses from large planetary volcanoes into space. This work may also tell us about the atmospheres of some hot exosolar planets. 3. How do metallic cores form and differentiate? The Earth like all terrestrial planets has an iron core. In the case of Earth it is partially liquid, so convects, generating a magnetic field. How do such cores form and then crystallise? We will measure isotopic variations in vanadium, chromium, nickel, molybdenum, palladium and tungsten in meteorites, which together with experiments, will provide new insights into core formation and crystallisation in early planetary embryos as well as larger objects. These are expected to also shed light on the nature of the Moon-forming impactor Theia.4. How do rocky planetary interiors respond to orbital stresses? On Earth we are aware of tidal forces from the Moon that cause the interior of a planet to move. Shortly after the Moon formed it was very close to Earth - it would have occupied a third of the night sky! So the tidal forces would have been vastly bigger. Yet we do not know much about how a rocky planet responds to such huge stresses. We will conduct laboratory experiments to evaluate this. 5. How do planetary crusts influence atmospheric evolution? One of the most important aspects of the development of habitable worlds is the formation of an atmosphere. However, the release of one of the most important and simple of elements, hydrogen, is not well understood. There are ideas emerging from climate modelling and origins of life studies that we will test with new experimental and modelling investigations of hydrogen generation through the interactions between water and rock.