Comet Hartley 2 moving eastward (up) in the constellation Cassiopeia on October 2, 2010. You can see the comet as it occults some mag 11 or so stars. The video was captured at the Starhoo Obsevatory (www.starhoo.com) in Lakeville, MA.
A comet may have hit the planet Neptune about two centuries ago. This is indicated by the distribution of carbon monoxide in the atmosphere of the gas giant that researchers have now studied.
Here are all the missions NASA has sent past Earth orbit, for which it now watches and waits for data. Some will be finished in a few years, others have been flying for nearly 40, slowly gathering data and beaming it back to Earth, or potentially waiting to be discovered by someone else out there.