Comet Hale-Bopp

(Photograph) - Astronomers at Queen Mary and Westfield College, London, and Queen's University, Belfast, are studying Comet Hale-Bopp as it passes the sun.

According to Iwan Williams of QMW, the comet's nucleus, made of snow and dust, is only 25km across and not visible even with telescopes. But as the comet passes the sun, the melting snow and dust particles form a cloud around the nucleus which is then pushed by the sun's radiation to form the distinctive tail behind the comet in a direction away from the sun. The dust particles reflect sunlight, making the comet clearly visible from earth. The British researchers have recorded jets of dust coming from the nucleus, which they say suggests the nucleus is covered by dust and that rather than uniformly melting, dust and water is released through vents where the surface cover has thinned.