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British scientists have identified the longest comet tail ever recorded. The tail belongs to Comet Hyakutake and measures over 570 million kilometres in length - which is nearly four times the distance between the Earth and the Sun. If the ghostly comet tail could be seen with the naked eye from Earth it would stretch almost halfway across the sky.
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The scientists, led by Geraint Jones of Imperial College, London, discovered the comet tail when analysing data from the magnetic field instrument on the spacecraft Ulysses - a joint European Space Agency/NASA mission - that flew through the comet tail.
Ulysses orbits the Sun and was measuring the solar wind [a stream of charged particles constantly flowing from the Sun] when it inadvertently strayed into the comet's tail. "As Ulysses crossed the comet's tail the instruments recorded some very odd readings, and we couldn't work out why" said Geraint Jones.
"Although the change in the magnetic field was typical of what we would expect in a comet tail, there was no known comet in the area, so we initially discounted the idea" he continued. "When we looked again at the instrument readings we were convinced it was a comet, so we decided to look further into space and realised that Ulysses had crossed the tail of Comet Hyakutake, which was then far away in another part of the solar system - making it the longest comet tail in history!"
The discovery, which is reported in this week's issue of "Nature" [6/4/2000], is providing an unexpected bonanza for scientists working on Ulysses. Geraint Jones added, "Finding and identifying the comet's tail is only the beginning. Now we can learn a great deal more about what conditions are like in comet tails by studying data from instruments that have actually been there, rather than trying to work it out from observations made from the Earth."
Prof. Ian Halliday, CEO of the Particle Physics and Astronomy Research Council, the UK's strategic science investment agency and funding body for the Ulysses team at Imperial College and Queen Mary and Westfield College, London, said, "Only three comets have ever been encountered by spacecraft before and none so far from the Sun - this is a significant discovery by British scientists using technology that they developed. I am extremely pleased to see our investment in Ulysses instrumentation providing such a wealth of important data". Halliday added, "In 2003 the European spacecraft Rosetta, in which the UK has a major stake, will be launched to rendezvous with the comet Wirtanen. We are funding instruments for a special probe that will look at how a comet tail actually starts. The probe will also land on the comet's surface and analyse the structure and composition of the comet's material, providing a vital insight into the origins of our own Solar System".
For further information on the Ulysses mission see: http://sci.esa.int/ulysses
For further information on the Magnetometer Instrument see: http://www.sp.ph.ic.ac.uk/Ulysses/
UK involvement in Ulysses Imperial College, London is the Principal Investigator [lead institution] for the Magnetometer instrument, and Co-Investigator for the COSPIN [Cosmic Ray and Solar Particle investigation] and EPAC [Energetic Particle Composition experiment] instruments. For more information about the Magnetometer instrument see: http://helio.estec.esa.nl/ulysses/archive/expt/vhm_fgm/vhm.htm
The University of Birmingham is Co-Investigator institution for the HI-SCALE [Heliosphere instrument for Spectra, Composition, and Anisotropy at Low Energies] experiment.
The University of Kent at Canterbury is a Co-Investigator for the dust experiment.
Ulysses' unexpected encounter with the comet has provided useful scientific information about the make-up of comets. Most comet research has been done from the ground and the few spacecraft to encounter comets have been much closer to the nucleus. This is the first "on-site" information we have on the composition and structure of comet tails so far from the actual nucleus of the comet.
The Particle Physics and Astronomy Research Council (PPARC) is the UK's strategic science investment agency. It funds research, education and public understanding in four broad areas of science - particle physics, astronomy, cosmology and space science.
PPARC is government funded and provides research grants and studentships to scientists in British universities, gives researchers access to world-class facilities and funds the UK membership of international bodies such as the European Laboratory for Particle Physics, CERN, and the European Space Agency. It also contributes money for the UK telescopes overseas on La Palma, Hawaii, Australia and in Chile, the UK Astronomy Technology Centre at the Royal Observatory, Edinburgh and the MERLIN/VLBI National Facility.
PPARC's Public Understanding of Science and Technology Awards Scheme provides funding to both small local projects and national initiatives aimed at improving public understanding of its areas of science.
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