A couple of days ago the space probe Stardust/NExT zoomed past comet Tempel 1 and the images are being made available at http://www.jpl.nasa.gov/news/stardust/
5 years or so ago the probe Deep Impact smashed a massive (370 kg) chunk of copper into the comet to try to stir up sub surface material. Stardust/NExT has re-imaged that impact site, though it's difficult to see in the above image. Tempel 1 is 7.6 x 4.9 kilometres across so it's a pinprick somewhere between the two craters at the centre of this image.
Hopefully, as the images are processed and enhanced, it will become more visible.
UPDATE: Phil Plait has identified the site, see here.