Hobbies And Interests
Scale
One topic with respect to space probes is the sheer scale of the universe that they are sent out to explore. The New Horizons probe, for example, which is bound for Pluto, is the fastest man made object ever built, and is traveling at an astonishing 31,000 miles per hour. On December 29th, 2009 it passed the halfway mark between the Earth and Pluto, but will not reach Pluto until July of 2015.
Messages
Another topic with respect to space probes is the messages that some of them carry. The space probes Pioneer 10 and 11, for example, both carry plaques attached to them, which denote a number of different things about the human race, including where Earth is located. Should any intelligent life in another galaxy find it, they would then be able to use that information to find Earth. Perhaps, if the life forms that found it were technologically advanced enough, they could then travel to Earth.
Course
Space probes are also a cool topic because of the amazing, careful planning that goes in to plotting their course. There are a myriad of competing gravitational fields in our solar system that move as the planets move, and a course through those fields has to be plotted in such a way that the probe is not taken off course. Astronomers not only plot a viable course, they will also use the gravitational fields of large objects, like planets, to help speed up probes.
Receiving Probes
Implicit in the act of sending probes out in to the galaxy and the universe is that there is the possibility, however slim, that humanity may one day receive a probe from some distant civilization that had a similar idea. Perhaps, if this other civilization was as forward thinking as humanity has been, they would denote their location in the galaxy, and we could then send them a probe back. It might take hundreds of thousands of years to reach its destination, and would be a rather delayed conversation, but it would be a conversation.