The outer space medium (with radiation and low temperature) coupled with interstellar distances acts as a very effective biocide, even against something very re

The outer space medium (with radiation and low temperature) coupled with interstellar distances acts as a very effective biocide, even against something very resistant as tardigrades. The way I see it, about encountering free floating extraterrestrial life, either sole or riding an asteroid, the most we can realistically expect is for complex organic matter, remains of once functional biological mechanisms, that would present in itself definitive evidence. The aforementioned natural barrier is a bit to high and too unrewarding for unguided evolution to address (regardless of allotted time). For something to be able to traverse long distance in outer space medium and avoid degeneration, the destructive factors need to be actively countered, therefore the other kind of evidence must be something undoubtedly engineered by an intelligent creatures, be it probes or vessels preserving organic matter.