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Isotopes and the origins of the Solar System

Tuesday 10 November 2015, at 6:30 PM - 7:30 PM
Wallace Lecture Theatre Cardiff University Cardiff, CF10 3AT

The 2015-16 monthly series of evening lectures in the School of Earth and Ocean Sciences will consider how isotope analyses have enhanced our understanding of the natural world.

Professor Alex Halliday (University of Oxford) will deliver the third in the public lecture series ‘A Mass-ive Difference: the role of isotopes in solving major problems in Earth and planetary history spanning origins to human influences’.

The Sun formed 4.57 billion years ago from the collapse of a portion of a molecular cloud of gas and dust. The motion in the cloud became a rotating star surrounded by a swirling circumstellar disk. It was from this disk that the planets and smaller objects of the Solar System formed. Meteorites are pieces of debris that have largely been derived from very early protoplanetary objects formed in this disk. They provide a fascinating archive of information about its history and include the earliest objects that have yet been identified that formed in the Solar System as well as grains of the dust from the original molecular cloud. Whether in gas or dust, nearly all the elements in the cloud except hydrogen and helium were largely made in pre-Solar stars by a process called stellar nucleosynthesis. Light elements (up to iron) were normally made by fusion under intense pressure. Heavier elements were made by irradiation mainly by adding neutrons.

Atoms of the same element with differing numbers of neutrons are called isotopes. Some are unstable (radioactive) and decay to isotopes of other elements which is how the diverse elements heavier than iron were made. The proportions of the different isotopes provide a kind of fingerprint of the stars that predated our Sun in this neighbourhood of the Milky Way. These include some that were probably large (say 20 times the mass of our Sun) and formed underwent supernova explosions. Isotopes also provide a method for determining the timescales of planetary growth, and a fingerprint of the various components and processes. It appears that most planetary objects grew early, within a few million years, except for the Moon which was formed after at least 30 million years in a late collision between Earth and another planet Theia. How that happened is still a matter of debate. Most satisfactory simulations of the impact derive the Moon’s atoms from Theia. The isotopes provide strong evidence that the atoms came from Earth. At present we do not have a satisfactory explanation for how the Moon formed.

Event Details
Tuesday 10 November 2015
6:30 PM - 7:30 PM
Cardiff University
Wallace Lecture Theatre
Cardiff University Cardiff, CF10 3AT