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.

  1. 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.

  2. 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!

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    $\begingroup$ Invasive species from a poorly sterilized probe would be a good start... $\endgroup$
    – stix
    Commented Jul 29, 2022 at 20:11
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    $\begingroup$ For the nuclear particle dispersal aspect, instead of an RTG the probe could use a nuclear fission fragment reactor, which could then shatter, of crack, or split, and disperse uranium dust through Europa. en.wikipedia.org/wiki/…. $\endgroup$ Commented Jul 31, 2022 at 3:07
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    $\begingroup$ This instantly reminded me of Subnautica. The giant spaceship that crashes into a mostly-oceanic planet has nuclear engines, that start leaking out radiations in a large radius and disrupts/kills the local fauna and flora. It is implied that if the character doesn't fix them, it could have harsh consequences on an even larger area, maybe even the entire planet. Unsure how accurate from a science standpoint this could be, but it is definitely an interesting concept to look at for this question. $\endgroup$
    – Matthieu
    Commented Aug 1, 2022 at 10:29
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    $\begingroup$ Why are people answering in comments? I hate to be "that guy", but it's annoying, and I'd like to see an answer on it. $\endgroup$
    – n00dles
    Commented Aug 1, 2022 at 12:35
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    $\begingroup$ Your first option is more plausible than you think. Although NASA does go to great lengths to reduce cross contamination that's no guarantee that they will continue to do so or that others will follow those same guidelines. Tesla came under fire a few years ago for launching a car that hadn't been cleaned into an orbit that could reach mars. ITs not unlikely that someone would either forget to decontaminate the probe or just not care to. $\endgroup$ Commented Aug 3, 2022 at 18:57

9 Answers 9


The Europans are terrified of what the probe means.

The probe does not do anything more than it was supposed to do. But it is recognizably an artifact of an advanced alien culture. That means aliens are real, and more powerful than the Europans.

Europan societies were paranoid and xenophobic before, and under the strain of this new knowledge they collapse. There are riots and mass suicide. Conspiracy theories proliferate. Religious cults form and attack the populace. A society of one alien type turns on another, wiping it out. The most advanced aliens suffer a military coup and subsequent Khmer Rouge like violent purge of supposed alien sympathizers.

The moon Europa itself is ok. The alien societies dissolve into chaos.

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    $\begingroup$ Not a bad idea, but doesn't really fit with the story I'm going for. Only the advanced society knows where the probe came from, as the rest of society has no idea anything exists beyond the ice 'roof' of their world. I do think this might apply to the advanced civ though, and it's part of why they would go to such extreme measures to "answer" the probe with an assault of their own. $\endgroup$
    – Brooke
    Commented Jul 30, 2022 at 4:38
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    $\begingroup$ @Brooke - I was inspired by your other question about what the advanced civilization does. You could have them be the ones to wipe out one of the less advanced societies in their xenophobic terror, this to presage what would come next. $\endgroup$
    – Willk
    Commented Jul 30, 2022 at 15:39
  • $\begingroup$ @Brooke: Your mention of an ice roof brought to mind a favorite story of mine: James Blish's Surface Tension. $\endgroup$ Commented Jul 31, 2022 at 15:57

Leaking RTG

Numerous space probes in the past have used Radioisotope thermal generators as a source of power in the outer solar system, where solar panels are less useful. There have even been some speculative proposals about using heat from an RTG to melt through the Europan ice in order to release a submarine drone into the subsurface ocean.

Lets suppose a space probe with an RTG crash landed, and the sealed container containing the Plutonium-238 was breached. Heating from the radioisotope could be enough to melt through the ice.

Once in the water, It would likely sink to the sea bed. As a neutron and beta emitter (when factoring in short lived decay products), it would be well shielded by the water, and any radiation dose would be limited unless a Europan lifeform got very close to the remains of the RTG.

However, if the radioisotope was in a more dispersible form (perhaps small dust particles), then Europan creatures could end up absorbing small particles of the radioisotope (through gills, or biologically analogous structures). Internally, this would be deadly. Any creatures unlucky enough to absorb some of the plutonium would likely receive a lethal dose, and die soon after. If their environment was naturally low in radiation (due to water shielding, and the Hydrothermal vents not spewing up anything too radioactive), it's possible they would not have evolved much radiation tolerance, and would be very susceptible. Any creatures in a wide area around the crash site could die, along with those that fed on them, those that fed on them, and so on.

Although this may not be enough to trigger a moon-wide ecological collapse, it could certainly have dire effects that reached far away from the crash site, causing the death of many creatures.

  • $\begingroup$ Neither of the common RTG fuels (plutonium dioxide and strontium titanite) dissolves in water, and both are fairly tough ceramics. $\endgroup$
    – Mark
    Commented Aug 1, 2022 at 22:58
  • $\begingroup$ They don't need to dissolve, just disperse as dust. Any impact big enough to break the RTG's containment is going to be enough to crack/break the radioisotope pellets and leave a fine dust that can drift with currents. $\endgroup$ Commented Aug 2, 2022 at 5:53

The Great Europan Oxidation Event (due to biological contamination)

Around 2 billion years ago (give or take), a clever species of Terran cyanobacteria figured out how to photosynthesize. The result was the Great Oxidation Event. The oxygen concentration in the oceans rapidly rose, followed by a rise in the atmospheric concentration of oxygen.

To some anaerobic organisms, oxygen is a deadly poison, disrupting their metabolic processes. Oxygen is highly reactive—it "wants" to react with a lot of chemicals, and if these are delicate biological molecules like proteins and DNA, well, too bad for the organism in question. Even aerobic organisms like us (those that require oxygen for their survival) have to have cellular repair mechanisms that can fix the problems that arise when oxygen molecules react with things they shouldn't react with. On Earth, the Great Oxidation Event caused a mass extinction of anaerobic organisms that could not tolerate the higher concentration of oxygen. Most of the organisms that survived were those that could evolve to cope with the increased oxygen levels.

In your Universe, the Europan ocean is largely anoxic (containing very little dissolved oxygen), and the higher organisms that evolved there are anaerobic. Chemically, oxygen gas for them is not unlike chlorine gas for us: deadly even at relatively low concentrations. It might even already be known as a deadly poison by your civilizations, and banned under the Europan equivalent of the Geneva convention. Then an improperly sterilized probe from Earth introduces a Terran microbe (not necessarily a photosynthesizing one) that tolerates oxygen and excretes it as part of its metabolism. The result is an unintentional act of warfare against the Europans that is simultaneously biological and chemical.


Biological contamination due to deliberate sabotage

Biological contamination due to microbes is the obvious answer. There are microbes on Earth that can live off redox gradients in the ocean, and those microbes are found in small numbers everywhere on Earth, not just in the ocean, so it's not implausible that a probe could be contaminated with them.

However, as you said, space agencies go to great lengths to avoid such contamination, and for a mission to a world like Europa that could be habitable this would be an even greater concern. You could just say that contamination happened anyway, by accident, but as you say that might be "too easy", storytelling wise.

So why not have the contamination be deliberate instead? Someone with access to the probe managed to sneak in a sample of hydrothermal vent bacteria and smear it on part of the probe, somehow circumventing all the security protocols that presumably exist to prevent that.

Why would anyone do such a thing? I don't know, it's your story. Perhaps they had prior contact with some nefarious faction of Europans, or maybe they had their own more Earth-bound reason, it's up to you.

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    $\begingroup$ Terran idealogs who believe Earth is the only source of life, and it is our species holy mission to spread life throughout the cosmos would be a good idea here. Panspermia! $\endgroup$
    – DWKraus
    Commented Jul 31, 2022 at 13:45
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    $\begingroup$ Addition as to why those microbes would be harmful: They are (by chance) stronger than the local ones and absolutely unedible for the population, who depend on their local geysir microbes for sustenance $\endgroup$
    – Hobbamok
    Commented Aug 1, 2022 at 11:54

You could crash Europa into another moon

The Planetary Protection Program checked your probe very carefully. But not carefully enough... a microbe escaped their notice.

One microbe? What can one lousy microbe do? Well, it lays down a slime of polysaccharide that nothing on Europa can digest. The microbe chokes off competition, dominates the ecosystem, and inundates the ocean in slime until it has the consistency of fresh-hocked mucus.

Well that's terrible. But life will adapt, right? Ah, but you're forgetting moon-moon resonance. The sloshing of the tides on one moon of Jupiter interacts with that on another moon of Jupiter. (The precise depth of the ocean affects what it interacts with, and I expect viscosity would have a similar impact) When they are in sync, orbits remain stable. When they're near sync... orbits slowly change. And as the ecology evolves, changing the overall viscosity of the ocean, the moon gradually adjusts its orbital resonance, which is to say its orbital period, which is to say its orbital radius. It uses the push of another moon, via its ocean, to move in or out.

Perhaps it might have simply been ejected from Jupiter, to become a planet of its own in an odd elliptical orbit. But as it so happened, Europa was unlucky, and a close approach threw it into an elliptical orbit that ended in a collision.

Yes, that one single microbe turned these two moons into the dramatic Rings of Jupiter that vacationing lovers admire today.

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    $\begingroup$ I do like the idea of how the microbe could specifically cause the ecological disaster. I'm not completely sure I understand the moon-moon resonance part, and it sounds like it might create too big of a problem to fix/survive. $\endgroup$
    – Brooke
    Commented Jul 30, 2022 at 15:26
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    $\begingroup$ I am not convinced that the orbital changes could happen on a story-relevant timescale. $\endgroup$ Commented Jul 30, 2022 at 15:40
  • $\begingroup$ @JohnDallman I stayed mum on the timescale for a reason! :) I can't think of a way to rush this, but maybe you can put folks on ice or make them live a really long time. $\endgroup$ Commented Jul 30, 2022 at 16:16
  • $\begingroup$ A very creative sequel! :) $\endgroup$ Commented Aug 1, 2022 at 20:56

Unfortunate impact

Your probe got lost. The landing was not an intended landing, it was a high velocity impact. The heavy apparatus, size of a train wagon, penetrated the ice at a very unfortunate place: a particularly thin spot. Below that spot, the largest biome of Europa existed, profiting from the sunlight. The ice ceiling breaks and your biome gets exposed to space. Through the pressure, loads of water vapor and atmosphere start to leak away. The small crack results in a huge rupture.. and large parts of Europa's ice ceiling are now getting unstable. Several of the advanced civilization's cities are devastated, killing millions.

This event is now called the Europan genocide. Our fault. There's a tribunal for it.


Biological contamination.

This is probably the simplest answer. One of the probes functions during its mission is to test and if possible return for further study samples from Europa's hydrosphere. So far so good - the lander and sampler modules have been carefully sterilized to the highest possible standards back on Earth.... but! There's an accident.


A) part of the probe wasn't as carefully cleaned (because it was not supposed to come into contact with liquid water) but does due to unforeseen problem (ice quake?) or;

B) post sterilization there was accidental cross contamination of previously 'clean' components like parts of the drill shaft or head.

Either way a microbial contamination from Earth reaches liquid water and starts to make itself at home to the determent of the local ecology. (The problem is a well documented concern in the planetary lander community and great lengths are gone to try and avoid it.)


Catalytic reaction.

The probe has a lot of sensors and parts that contain specs of particular metals in a purified state. A lot of them may act as catalysts, maybe the probe does not have a lot of platinum, but nickel might be enough. Imagine the probe immersed in water near a thermal vent surrounded by a lot of compounds. As soon as the catalyst enters into contact with the right compounds the chemical reaction is triggered and the currents spread around the result.

I don't know the composition now and I don't know exactly what could be the reaction, but the number of possibilities is quite big. What could avoid the extreme consequences? Catalyst poisoning. The damage would be one off.

Update: On a second thought I realised that nickel is common in meteorites. So if it were dangerous the disaster would have already happened. You'll have to find a better and less common catalyst.


The probe acts as a Siren

From Wikipedia:

In Greek mythology, the sirens were humanlike beings with alluring voices

Further, a speculative etymology interprets the name to mean:

one who binds or entangles through magic song [ibid.]

By unfortunate coincidence, this is what the probe does. It became disoriented in the Europan ocean and then trapped in some kind of crevice, where it entered a failure state in which it repeatedly tries to signal Earth for help. The message never reaches Earth, and a response never comes back, so the probe continues to send its signal periodically until its battery dies.

The Europan creatures have sensory organs that are receptive to the signal coming from the probe, like how sharks and other sea creatures can sense the electrical energy in the muscles of their prey. The Europan perception of the probe's SOS signal is strange but alluring, instilling in nearly every individual an overwhelming desire to repeat the experience. If they "hear" it, they swim towards the source and then wait for it to happen again, sitting patiently to the exclusion of all else. Most starve to death while waiting to bask in the next transmission.

Most radio waves don't travel very far in water, certainly not the frequencies that we use for space probes. This means that the deadly siren signal can only be heard by Europans who are very close to the probe. This fact is crucial to how the danger spread: two Europans went to investigate the probe, and one of them became ensnared. The other went to fetch help. Because the signal is brief and intermittent, nobody figures out what the safe distance is, and all the scientists and leaders who investigate end up getting snared.

These days, Europans come to the site because they've heard rumors. Some hear about a great treasure that is unimaginably beautiful. Others hear of a mountain of dead. All who go fail to return.


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