I've always wondered why we're so hellbent on having our probes being so sterile.
Purely for (important) scientific reasons.
- IF we find life there AND can be certain that our probes didn't bring it there, we'll have not only a sample of the size "1" (Earth, we know there's life here), but "2" or "3" (Enceladus, and Europa) out of 3 places that we identified as likely candidates. Make that four, should we actually discover life on Mars.
So, that would be the most "optimistic" result that we might discover. IN THAT CASE the chances that life is a universal property of planets with liquid water rise dramatically. In which case the chances of this galaxy bearing more than one technologica society are much higher. Which may be good or bad news, as we may find ourselves no longer at the top of the food chain. - If we find no life anywhere else, the likelihood of the universe being a largely sterile place increase dramatically.
- For results "in between" (say, one other place out of four candidates in this solar system) scientific stidy will be most interesting. In that case it's particularly important to have no contamination with Terran bacteria because only then can we study a truly alien life form. Once that contamination occurs we can no longer know which elements that look familiar are actually familiar because we brought it there, and which elements developed independently.
Once that we are reasonably certain whether or not these three solar candidates bear life or not the decision to "spread life" (=
our life) is essentially a political decision, not a scientific one. But for the science part, we only get one chance to do it right, and at the moment we don't seem to have the technology to ASSURE that our space probes are
free of contamination. Our bacteria arfe small, and in huge numbers. We can easily kill 99.9999% of all bacteria on a satellite, but the scientists want 100%, not rounded up. That is a challenge that we aren't ready to meet, yet.