On the night of the 23rd of October, Comet 17P/Holmes underwent an outburst that increased its brightness in a factor of a million on the following days.

The Isaac Newton Telescope (INT) pointed to the comet just after sunset on the following night to the outburst, and it detected a highly centrally condensed coma with no signs of a tail. The coma had extended out to 37,000 km from the nucleus, and the outer edge was almost perfectly circular. This distance implied the dust was moving at least 0.2 km per second (800 km per hour) from the central nucleus. Image processing showed that the material was currently leaving the comet towards the South East.

Professor Tim Naylor and PhD student Cameron Bell from the University of Exeter were the observers at the INT and have been tracking the evolution of the comet with the help of Professor Alan Fitzsimmons from Queen's University Belfast. The accompanying image shows an expanding circular cloud of gas and dust emanating from the nucleus, together with a brighter cloud of material.

INT image of comet 17P/Holmes processed to show the inner coma structure. Credit: T Naylor / A Fitzsimmons / C Brunt / ING. [ JPEG | JPEG and Earth for comparison].

More information:

• UK Astronomers Home in on Exploding Comet, STFC press release, 31st October, 2007. Available versions: HTML | HTML local copy.