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John Chambers has refined and expanded an alternative scenario for the formation of the asteroid belt in collaboration with George Wetherill, Carnegie Institution of Washington, USA. Using numerical simulations on computers, they have shown how planets may have formed in the asteroid belt. However the orbits of these planets were made unstable by gravitational perturbations by the giant planets Jupiter and Saturn. As a result, the planets in the asteroid belt were all lost, falling into the Sun or being thrown into interstellar space, leaving no planets in the asteroid belt today.
Building on this work, John Chambers and collaborators at Nice Observatory, France, have shown that most small asteroids would also have been lost, leaving only the ones we see today. They have also explained why many of the remaining asteroids have highly eccentric and inclined orbits, unlike the planets in the Solar System.
This same collaboration has shed light on an old mystery: why the Earth has water and organic material on its surface. This is a long-standing problem since theories for the origin of the Solar System predict that planetary building blocks (``planetesimals'') that formed at Earth's distance from the Sun should be very dry. For a long time it was thought that comets collided with the young Earth, bringing the water and organic material needed for life to form. However recent work has shown this idea is untenable. The Nice workers and John Chambers have shown that protoplanets forming in the asteroid belt can supply this material to Earth instead. In collaboration with workers at NASA Ames, John Chambers is extending this theory to extrasolar planetary systems.
John Chambers has made new detailed computer simulations of the origin and formation of Earth and the inner planets. These have overcome many shortcomings of earlier simulations, and produce systems of planets that resemble those in the inner Solar System in many respects. However some differences remain, suggesting that our planetary system may be special in some way. Dr Chambers is now examining whether this is related to events that occurred in the asteroid belt and outer Solar System, with the aim of developing a single coherent model for the formation of our planetary system.
``Mercury'', the computer package for calculating orbital evolution developed by John Chambers, has now been made publicly available on the Armagh computer FTP site. Collaborations with Marc Murison at the US Naval Observatory and others should further improve this package in the near future.
During the year, John Chambers undertook scientific collaborations with: J.J. Lissauer and E. Rivera at the NASA/Ames Research Center, on the formation of the inner planets and the Moon; P.N. Sleep and B. Jones at the Open University, on the stability of terrestrial planets in extra-solar planetary systems; A. Morbidelli and J.-M. Petit at the Observatoire de Nice, on the origin and early evolution of the asteroid belt; M. Kress and R. Bell at NASA/Ames, on delivery of volatile materials to Earth-like planets in extra-solar planetary systems; E. Thommes and M. Duncan, Queen's University Canada, on the formation of the outer planets and the asteroid belt; M.A. Murison at the US Naval Observatory, on developing better computer algorithms for solving the N-body problem; G.W. Wetherill at Carnegie Institution of Washington, on planet formation and the formation and evolution of the asteroid belt; and G. Stewart, University of Colorado, on N-body integrators.
John Chambers also served as external examiner for a PhD student at Oxford University, refereed a number of papers and grant applications for PPARC, NASA and the Austrian Science Council, and presented a number of papers at colloquia and scientific conferences.