Who cares about those other galaxies...they're full of foreigners anyway

Derelict rocket stages that propelled four spacecraft toward the edges of our solar system and beyond are likely carrying Earthly bacteria out into the galaxy....

“The upper stages were not required to be sterilized,” said John Rummel, senior scientist for astrobiology at NASA. There was just one big directive: “Their requirement was not to hit any of the planets in our solar system,” a caution necessary since the rocket stages would almost certainly play host to large numbers of Earthly bacteria.

Link: SPACE.com -- Old Rockets Carry Bacteria to the Stars