This optical HST image of the impact site on Jupiter was collected by Heidi Hammel (SSI) and others using HST's Wide Field Camera 3. This camera is still new and not fully calibrated yet, since it was installed only two months ago by Shuttle astronauts. Nonetheless, it is still able to produce a magnificent image. The current estimate for the impactor diameter is about a third of a kilometer. See this press release for more details.
Above is an infrared image of Jupiter, as observed by Paul Kalas, Michael Fitzgerald and Franck Marchis at the Keck telescope. Note the bright spot, which overlaps the mysterious black spot that recently appeared on Jupiter (see earlier post, below), indicating that this spot is indeed hot. This supports the notion that Jupiter was indeed hit by an impacting comet or asteroid. See New Scientist for more.
Anthony Wesley from Murrumbateman Australia reports seeing a black spot in Jupiter's atmosphere. Black spots on Jupiter are reported from time to time, the most famous example of which was due to the impact of comet Shoemaker-Levy 9. That comet orbited Jupiter unseen until 1992, when it was disrupted by that planet's gravitational tide into about 20 fragments during a particularly close approach to the planet. Those fragments then struck Jupiter in 1994, resulting in similarly black (but much larger) bullseyes. Followup observations of this new spot will hopefully reveal whether it might be due to an impact by a comet or asteroid, which is a very rare astronomical event. Stay tuned.