When the Deep Impact probe hit Comet 9P/Tempel, there was almost no change in brightness. ... This outburst by Comet Holmes is extreme!
On the unprecedented brightening of Comet Holmes, as quoted in . Within the space of a few hours between 23-24 October 2007 it brightened from a very dim and obscure object requiring powerful telescopes to see into one easily visible to the naked eye.
We have to beef up our searches, which are now pretty dismal, so we can find out about these things before we get hit. ... It takes a dramatic event to get people's attention, and we thought the comet crash with Jupiter might have done the job. ... we tend to ignore an extraterrestrial hazard that could reduce the planet to rubble. ... What we really need is a good scare.Brian G. Marsden