Top ten spacecraft

5. Pioneer 10
As humans we want to learn about the world around us. But the world is pretty much all discovered -- apart from the sea, but that's cold and wet -- so the next step is a voyage through the solar system to really get a sense of how insignificant we are.

Pioneer 10 was the first spacecraft to travel through the asteroid belt, and is the first artificial object to leave the solar system (although there's considerable debate about what constitutes leaving the solar system).

Originally designed to report on the asteroid belt, Pioneer 10 is powered by a radioisotope thermoelectric generator, mounted some distance away from the body of the craft, to prevent messing up the instrumentation.

The last time we spoke to Pioneer 10 was on 23 January 2003, and conversation had all but dried up by then. With Pioneer unprepared to discuss such things as telemetry, it barely acknowledged our existence, as it travelled on to bigger and better things. In 2 million years or so, Pioneer 10 will reach Aldebaran, by which time it will be nothing but a flying memorial to a planet Earth long since destroyed by mutant camels.

Photo credit: NASA