Blazing a trail of primordial dust

(l-r) Professsor McDonnell and Professor Taylor outside Halley's former house in Oxford

Comets played a role in the origins of life on Earth and might equally bring about its end. This view of these spectacular heavenly visitors was expressed by Professor Tony McDonnell of the University of Kent, giving the eighty-eighth Halley Lecture in the University Museum. In contrast to the ancient belief that comets were harbingers of fate or the souls of the great departed, the prevalent view today is that comets are made up of debris from the primordial cloud from which the main bodies of the solar system, the sun, and the planets formed. As pristine examples of the primordial material from which the Earth was made, and some if not all of our atmosphere derived, comets are the focus of much research, including unmanned space missions such as Giotto, Stardust, and Rosetta. The Halley Lecture was instituted at Oxford—alma mater and home to the eponymous seventeenth-century meteorologist, oceanographer, and planetary astronomer—in 1910, one of the years in which the comet, whose return he famously predicted in 1705, travelled close to the earth. Professor McDonnell was one of the leading academics involved in planning and monitoring the 1986 Giotto mission to Halley's comet. During the lecture, he showed a remarkable film of the nucleus of the comet, as seen from the spacecraft. Made of a material resembling frozen soil, the nucleus is a potato-shaped object about fifteen miles long. Jets of gas and dust streaming from it give rise to the spectacular tail, millions of miles long, which we see from Earth. Comet Hale-Bopp provided a similar spectacle earlier this year. The lecture, organised by Professor Fred Taylor, Head of the Atmospheric, Oceanic, and Planetary Physics Department, was preceded this year by a meeting of fifty top UK planetary scientists. Under discussion was the new Rosetta mission to comet Wirtanen—a recent research focus for the Oxford department. Following the lecture, Oxford's planetary physicists and their guests visited Halley's house in Queen's Lane and the Turf Tavern, assumed to be a hostelry frequented by the great astronomer.