This morning EPOXI, the spacecraft formerly known as Deep Impact, flew within 435 miles (700 km) of the nucleus of Comet 103P/Hartley 2. Images taken during the encounter are being downloaded from the spacecraft throughout the day. A few of the images have been released by the EPOXI team and can be found here.
The nucleus which is 1.2 miles (2 km) long and only 0.25 miles (0.4 km) wide at its narrowest section resembles a dog bone. In fact, it looks like a contact binary which is an object that consists of 2 main masses held together by gravity. The smooth narrow section being made up of fine material around the contact point. Recent observations suggest this shape may be common among comet nuclei. Comet 8P/Tuttle is known to have this shape and even 1P/Halley may be another example. This is just conjecture on my part and much better analysis will come from the EPOXI team in the coming days.
Congratulations to the EPOXI team for a job well done not only with the Hartley 2 flyby but also with the Tempel 1 encounter and the cruise phase extrasolar planet observations!