I'm working on a story involving life on Europa (or at least a place just like it) being upturned dramatically by contact from a probe sent from Earth. Found this community while researching, and have found a lot of great ideas. I know the chances of life, let alone intelligent life, are pretty slim on Europa, but I'm ignoring that for the sake of the story. The driving force of the story is that a probe that's come from Earth either crashes or malfunctions after melting through the ice.The probe sinks to the bottom of a trench and sets off some sort of ecological disaster/collapse, that then has cascading effects on the civilizations living there. I'm just trying to decide what's the most realistic/reasonable option for what causes this. It needs to be something that would start as a local area problem, but would spread.
Most of life revolves around thermal vents/chemosynthesis, etc similar to the life that lives at the bottom of our own oceans. Since a bacteria serves as the base of the food chains in those ecosystems, my first thought was to have some sort of unforeseen cross-contamination where some Earth microbe is killing off the bacteria, or interfering in the chain in some way. I don't know if it needs to be more specific than that to be reasonable, or if that's too dumbed-down. What microbe would reasonably be on a probe that survived the trip all the way to the planet, and then was able to not just survive exposure to the sea, but thrive? Is that too granular? It also feels a little too easy considering NASA, etc go to great lengths to prevent it.
Another thought I had was that if there was, say, a nuclear power element, maybe the crash/malfunction caused it to leak, and ....bad stuff. But I'd definitely need to do more research on this, as I suspect that's a very over-simplified version of events, and I imagine not very realistic once I start looking into it. Like, I feel like using nuclear power to power a probe is probably unrealistic (but I don't know), and if they did, the danger is probably smaller than what I would want for my story (not like there's going to be a Chernobyl in a space probe). So, kind of guessing this one is not a good idea, but maybe I'm missing something that would work from this angle.
I'm open to other suggestions if someone can think of a better explanation, but I'm guessing some version of (1) is my best bet.
Thanks so much for your help!