According to the article "Comet put on list of potential Earth impactors" by David L. Chandler, posted by New Scientist magazine today, Comet Catalina 2005 JQ5 has been added to the list of potentially threatening near-Earth objects.
Usually, when an object that might collide with Earth is first spotted, more observations are taken to rule out the possibility of a collision. However, according to the article, that's not quite what happened with this one:
Astronomers expected the addition of further observations to the calculations to rule out any possibility of a collision, as happens with most newly-seen objects.
But that did not quite happen. The comet's predicted pathway actually drew even closer to making a perfect bull’s-eye with the Earth - its predicted path passes within 1000 kilometres of the where the centre of our 12,700-km-diameter planet will be around that time.
But don't panic yet. The current odds of an impact are 1 in 120 million.