Acid erosion to things it touches. Fluctuations in electricity. Spread of disease. Lack of immunity to certain diseases.

  • $\begingroup$ Welcome to worldbuilding. Your question, as it stands now, is a bit problematic: you are basically asking for a list of possible issues, without giving us any hint of what is your judgment metric. What is unexpected for you? Where on Earth is this alien? What are the local conditions? Please take the tour and visit the help center to better understand how to structure a question. $\endgroup$
    – L.Dutch
    Jun 19, 2019 at 9:59
  • $\begingroup$ The only answer that could be given right now would be "yes", as any and all of the above are possible and have been depicted in various media. Are you looking for a list of such impact modi, or concerns about one specific alien species? $\endgroup$
    – zovits
    Jun 19, 2019 at 10:16
  • $\begingroup$ I’ve voted to close as this question is waaay too broad. The answer is a certain yes. Or no. Or maybe. It depends on you as a world builder. If you’re looking for examples of potential effects then ‘anything’ is valid, and we’ve got no way to judge what a good answer is. To start with Id focus on what kind of an answer you actually want and refine your question accordingly. $\endgroup$
    – Joe Bloggs
    Jun 19, 2019 at 11:44
  • $\begingroup$ That durned invasive Martian Red Weed has been a problem on Earth since 1898. $\endgroup$
    – user535733
    Jun 19, 2019 at 13:49

2 Answers 2


So to go through those things one by one:

  1. Acid erosion to things it touches. This depends on whether the alien's skin is acidic. If it is not there would be no reaction. If there were one, it would have troubles with any particles touching him that are flying around. He would need protection since they would influence his skin's biochemistry.

  2. Fluctuations in electricity. I think you mean that he causes noise in devices and other things, and disturbs electronics. Possibly, yes, if he himself is very electric. You see, electromagnetic fields cause those effects, and if with him comes a lot of unshielded electronics (which is unlikely cause it would also disturb their electronics) this would happen

  3. Spread of disease. and Lack of immunity to certain diseases. Very unlikely - No. You see, humans are very similiar, and when the white men came to America, they brought their human diseases and gave them to other humans. Not to say that Cross-species transmission does not happen: the Plague and Ebola are two instances where that happened. But we all share a LOT of similiar DNA. Which means Bacteria and viruses could with a bit of mutation infect other species. Aliens on the other hand would have a completly different biology. Even more so, if you decide to make your aliens acidic, it is impossible, since our viruses die due to their acidity.

  • $\begingroup$ So rather than disease/cross infection, an alien might for example suffer with physical issues, such as headaches due to different light levels for example? $\endgroup$ Jun 19, 2019 at 9:38
  • $\begingroup$ Very likely might their eyes be too 'good' or 'bad'. If they live in caves the light will harm their eyes but basically see everything at night (if they developed eyes in the first place), if they live in a very bright place, they will not see anything, it will be too dark for them. Same with noise and pressure $\endgroup$
    – bv_Martn
    Jun 19, 2019 at 9:42
  • $\begingroup$ Great. That's really helpful Thank you! $\endgroup$ Jun 19, 2019 at 9:45
  • $\begingroup$ @AvengingEarth you're welcome! if I solved your question you could select it as the answer to your question by ticking it right under the 2 voing arrows ;p $\endgroup$
    – bv_Martn
    Jun 19, 2019 at 10:14

1) Acid erosion - No. Alien would need to wear a hazmat suit if our environment is reactive for their race. Or, if they can walk "naked" on Earth - they will not be that reactive.

2) Fluctuations in electricity - to aliens as an organism no, for their tech - yes. Fluctuations mean that something emmits a lot of energy. Biological systems which emmit so much energy could not live long. As for alien tech - it will definetly not comply with part 15 of the FCC rule and will cause some interference in electric systems.

3) Spread of disease, lack of immunity - maybe, the latter is more likely. This can happen if aliens developed in exectly the same conditions as those we have on Earth (they are made from proteins). The point is that our biology on Earth is overwhelmingly larger than anything aliens can bring. This means that they would be "consumed" much faster than we are. But alien bacteria lacks native predators on Earth and can reproduce unconstrained. So the most probable scenario is: Aliens die from Earth germs (not even pathogen ones - some completly harmless yeasts would be enough), but then in a year or two some alien germ strikes back.

Another "unexpected" effects may be:

1) Radiation - in both ways (Aliens might be too radioactive and cause cancer or Earth radiation kills them)

2) Poison - also in both ways. Poisoning might be very slow and obscure at first (like havy metal poisoning)

3) "Any effective way of propulsion is also an effective weapon" - if aliens utilise, say, hover engines, with gas ejection speeds up to tens or hundreds of kilometers per second they could accidently destroy a lot of human structures.

  • $\begingroup$ Nah I hugely disagree with point 3. Seeing, how rare cross species infections are on earth, and those basically only with similiar species (no fish to bird or insect to reptile), I would think it is VERY unlikely, that diseases work either way. They have no hosts since they are not evolved for our kind of biology. Also poison. The only feasable poisons are metals. No biological poisons would affect the alien or vice versa, since poisons attack the body in specific ways, e.g. stop neurotransmitions. If their body's neurosystmes work differently, the poisons would not affect them. $\endgroup$
    – bv_Martn
    Jun 19, 2019 at 9:20
  • $\begingroup$ My point is that alien bilogical systems is would be so deifferent that is actualy sort of agar-ager substrate for each other. The will not be the diseases exchange, but completle harmless (in own environment) germs will spread and become infection in alien environment. Think of rabbits (or dogs, or frogs, or ...) in Australia! $\endgroup$
    – ksbes
    Jun 19, 2019 at 9:27
  • $\begingroup$ Yes, but rabbits and frogs are earthly creatures. They eat greens, and australia has greens. If you put them on mars they will die, even if there was oxygen. If their bacteria has no hosts here (bacteria is very specifically evolved to feast on one thing) it will just die. Yes maybe if they also base on proteins something like this MIGHT happen, but this is very unlikely, disregarding the chance of them even landing $\endgroup$
    – bv_Martn
    Jun 19, 2019 at 9:30
  • $\begingroup$ That exectly what I wrote in my answer: "This can happen if aliens developed at exectly the same conditions as we have on Earth (they are made from proteins)". Protein life is the only we know - so most likely any other life would be also protein based $\endgroup$
    – ksbes
    Jun 19, 2019 at 9:34
  • $\begingroup$ Yes yes, but not only is this very unlikely, even then their bacteria would be attacked by our fungi and vice versa. Because if they are so similiar they either have nothing to eat or they are so similiar they just are eaten. $\endgroup$
    – bv_Martn
    Jun 19, 2019 at 9:39

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