Scientists size up biggest comet on record

Scientists from UCL's Mullard Space Science Laboratory (MSSL) have identified a heavyweight contender for the crown of biggest comet on record. Dr Geraint Jones and his colleagues used data from the ESA/NASA Ulysses spacecraft to gauge the size of the region of space disturbed by the Comet McNaught. Analysis of magnetometer data shows evidence of a decayed shockwave surrounding the comet which was created when ionised gas emitted from the comet's nucleus joined the fast-flowing particles of the solar wind, causing the wind to slow down abruptly. In January and February 2007, Comet McNaught became the brightest comet visible from Earth for 40 years. Ulysses made an unexpected crossing of Comet McNaught's tail during this time, one of three unplanned encounters with comet tails during the 19-year mission. The other encounters included Comet Hyakutake in 1996, the current record-holder for the comet with the longest measured tail. Ulysses encountered Comet McNaught's tail of ionised gas at a distance downstream of the comet's nucleus more than 1.5 times the distance between the Earth and the Sun.