Particles (known as meteoroids) that come from interplanetary space, on the other hand, are natural.

ECONOMIST: Orbital debris

Because there are more DA14s filling interplanetary space than YU55s, a 50-foot asteroid can be found in a smaller volume of space, on average, and thus closer to Earth, than a 150-foot one.

CNN: A meteor and asteroid: 1 in 100 million odds

Then, there is the LIFE biomodule, which we piggybacked in the Grunt mission simply to get it into interplanetary space for as long as possible, 34 months in the case of this mission.

MSN: Salvaging Science from Stricken Mars Moon Probe: A Scientist's View - Technology & science - Space - Space.com | NBC News