via Astronomy Now.
When Comet 17P/Holmes outburst in 2007, it repeated a feat it performed in 1892. The 2007 gas cloud ejected from the surface of the comet expanded to greater than the size of the Sun and light reflected off the growing cloud lead to a brightening of the periodic comet.
Comets often outburst and it is believed that this is due to pockets of ice and gas under the surface warming up and expanding under the Sun’s increased heat as they approach. It is also believed ice within the body of the comet moved from a type known as amorphous ice to the type that we know and love, crystalline ice, releasing additional energy.
Outbursts rarely happen within range of a good telescope, so this opportunity was not one to be wasted. Images were taken all over the place, but one particular set was taken at the Canada–France–Hawaii Telescope in Hawaii in November 2007, within a month or so of the original outburst. Reanalysis of the images has produced an interesting result.
Rachel Stevenson of the University of California, Los Angeles (UCLA), along with David Jewitt also from UCLA and Jan Kleyna of the University of Hawaii applied a Laplacian Filter, which is a particular method of enhancing fainter details, to the image. They found ‘mini comets’, smaller chunks of material blasted off the surface of Holmes, each of which developed their own coma and tails. They travelled outwards from the comet nucleus at around 125 metres per second.
When Holmes returns to the inner sanctum of the solar system in 2014, astronomers will be on the lookout for either evidence of a new outburst or the effects of the last one.