Bug-Infested Space Voyagers

So far, out of all the thousands of space probes we earthlings have launched, only 4 have escaped the Solar System: Pioneers 10 and 11, and Voyagers 1 and 2. And each of them were meticulously sterilized before they began their never-ending trips to keep them from carrying some stray bacteria someplace it shouldn't go.

But there are actually 4 other machines nobody ever thinks of that are also wandering the starry reaches of deep space: the 4 rocket rocket engines, called "kick motors," that blasted the probes out of the Solar System. And these were not sterilized; the only requirement for them was that they not hit any of the planets.

Bacteria, we are finding, is unbelievably resilient and during hard times can power down into a hibernation state that no one knows the limits of. There are no nearby stars that our probes or rocket motors will pass for the next 40,000 years (and even then it will just be a little rinky-dink dwarf star), but eventually they will hit something. And who knows what will happen when Earth DNA finally seeds some far away planet?

Read more about this science fiction possibility in this interesting article.