Featured Essays aliens One More Reason the Aliens Might Be Avoiding Us Is the current location of our Solar System the reason no one’s coming to visit? By James Davis Nicoll | Published on March 13, 2026 Credit: NASA/JPL Comment 1 Share New Share Credit: NASA/JPL As previously noted1, there is as yet no unambiguous evidence of aliens. If there are aliens—which the evidence so far does not support, at all—they don’t seem to be anywhere in our neighbourhood. Why might that be? More importantly, which explanations haven’t been mentioned in my previous Tor.com/Reactor essays2? Could our current location be a sufficient reason to shun us, at least for the moment3? There might be a very good reason indeed. It goes by the innocuous name of the Local Bubble4. As anyone who has contemplated relativistic space travel knows, interstellar space is a hard vacuum, but it is not empty. The average density of the interstellar medium (ISM) is about half an atom per cubic centimetre (or if you don’t like fractional atoms, one atom per two cubic centimetres). In the Local Bubble, that density is 0.05 atoms per cubic centimetre (or one atom per twenty cubic centimetres). The Sun entered the Local Bubble about five million years ago. Because the Local Bubble is about a thousand light-years across, the Sun is still traversing the Local Bubble. Whether or not a rarified ISM is convenient or inconvenient for interstellar travel depends on the details of how starships might work5, and is beyond the scope of this essay. However, the process that created the Bubble depends on something that prudent aliens might want to avoid: our friend, the supernova. Supernovae are extremely energetic events which produce about as much energy as a galaxy. Side effects include enough neutrinos to deliver a lethal dose despite neutrinos’ miniscule interaction cross-section6, an impressive flood of electromagnetic radiation, and (thanks to the material ejected at high speed from the dying star) a shockwave propagating at up to 20,000 kilometres per second. That’s fast enough to cover the distance between the Earth and the Moon in less than 20 seconds. It’s what carved out the Local Bubble. Experts agree that you probably don’t want to be anywhere near a supernova. Sure, pretty lights and all, but those are hard to appreciate as one is being transformed into plasma. Further away, atmospheres are probably sufficient to protect against a direct radiation threat (unless the atmosphere is stripped away, in which case radiation probably isn’t your primary threat). The cost of that shielding might be an atmosphere transformed in ways inimical to life. Happily, while the effects of any given supernova reach across distances that are unimaginably vast on a human scale, they’re small potatoes on a galactic scale. You’d have to be very, very unlucky to be close enough to a supernova for it to destroy your ozone layer. Or alternatively, you could be a region where supernovae were for some reason unusually frequent. Any star-forming region will produce an assortment of stars ranging from a large number of small stars to a handful of massive stars. Any stars over eight solar masses will die in supernovae. The more massive the star, the shorter its life. What that means is shortly (on a cosmic scale) after a stellar nursery forms, there will be a brief but no doubt memorable flurry of supernovae. As the shockwaves expand, they will compress interstellar molecular clouds, triggering more star formation, resulting in more massive stars, and more supernovae. This won’t result in any sort of Known Space-ish apocalypse forcing us to relocate to the Andromeda Galaxy, but it is still not all that convenient. Earth seems to have been either lucky (if you’re a supernova fan) or lucky (if you are not) because evidence suggests a local supernovae peak dating back about two to three million years ago, for which we might credit the Scorpius-Centaurus Association, plus another one at six to nine million years ago, which might have been due to passing sufficiently close enough to the Orion OB1 stellar association as it carved out the Orion–Eridanus Superbubble. Since we’re here, it’s clear that the occasional flurry of supernova is no impediment to complex life or even technologically sophisticated civilizations. On the other hand, regions without supernovae must be even friendlier. Since it’s possible to predict supernovae millions of years in advance, why not avoid regions near stellar nurseries altogether? And if interstellar-capable civilizations do that, it’s no surprise we don’t see them around here. Of course, the above assumes a civilization whose planning timescales are on the order of hundreds of thousands or millions of years. Mayflies probably don’t need to worry about supernovae because even during flurries, the mean time between successive supernovae might be longer than the likely lifespan of such civilizations… but mayflies hardly seem likely to overcome the vast distances between the stars.[end-mark] No, I don’t feel like going through all 600+ pieces I’ve written for Reactor to link to previous articles on this subject. ︎The obvious explanation is that intelligent life is very rare and interstellar travel is difficult or functionally impossible. ︎Well, it could be the fact that the Sun is eight kiloparsecs from the centre of the Milky Way. That is, we are located out in the galactic sticks, where distances between stars are inconveniently large. But I’m looking for a more interesting reason. Also, close-packed stars have drawbacks that I will get into another time. ︎Astronomers are terrible at naming things. ︎Bussard ramjets can’t work (dang), but maybe there’s a way (handwaving here) to use the ISM as reaction mass. In that case, a thin ISM is a pain. On the other hand, maybe the ISM isn’t useful, and it’s just a source of radiation damage to starships. In that case, the thinner the ISM, the better. ︎Admittedly, if you’re close enough to get a fatal neutrino dose, you’re also close enough that the other supernova effects will almost immediately make lingering death from neutrino acute radiation injury an entirely academic matter. ︎The post One More Reason the Aliens Might Be Avoiding Us appeared first on Reactor.