Space is a damn scary place to be, at least according to movies like Alien: Covenant. If you’re not impregnated by facehuggers that vomit eggs down your throat, you’ll be eviscerated by xenomorphs who rip people apart for fun. It implies something dark, primal and aggressive lying in wait amongst the stars, and the idea of going to space is suddenly made 100% less appealing. It’s a horror film, naturally, but it does raise the possibility that our universe won’t be easily conquered.
New planets hide unknown threats, and some might be microscopic; it stands to reason that an alien world would carry alien bacteria if there really is life out there, and this is a threat our bodies aren’t ready for. While that isn’t nearly so horrific as a monster crawling its way out of your chest, the result wouldn’t be all that different – you’ll still die in a lot of pain and indignity.
Our immune systems are unprepared for such viruses, and they’d be unlike anything we’ve ever seen before. Consider the death-toll when conquistadors marched into South America: local Aztecs were unfamiliar with the likes of European smallpox, and their immune systems crumbled beneath the strain. It’s easy to see how extra-terrestrial germs or pathogens could have a similar effect on us (if they existed, anyway).
Accordingly, spores like those unleashed in Covenant aren’t unrealistic… even if what follows isn’t. The image of someone falling desperately ill for reasons unknown hits close to home. Cheerful, right?
We may not have to fend off inhuman creatures when we start colonising the stars, but our problems aren’t over nonetheless. We’d probably be better off with the xenomorphs: at least you can see them coming.