Featured Essays aliens Where to Look for Evidence of Alien Visitors to Our Solar System Scientifically speaking, here’s where we should start digging… By James Davis Nicoll | Published on January 8, 2026 Comment 0 Share New Share I occasionally wonder if the Solar System has ever been visited by extraterrestrials. If so, would sufficient evidence remain to prove it? It wouldn’t need to be technological: no need for a busted radio or a fully-functioning interstellar drive. Even something akin to a busted Folsom point would have fascinating implications. The most convenient place for such an artifact to turn up would be on Earth. That’s not likely, for reasons of scale. Without going into tedious detail, the earliest that life-bearing planets could have formed was long before the Earth actually formed. Any visiting ETs could have shown up any time during the whole 4.5 billion years of the Solar System’s history—shown up, faffed about, and then buggered off. To get a rough idea of what the age distribution might look like, assume a dozen aliens have swung by in the last 4.5 billion years. Rolling a forty-five-sided die, we get visit times of (in chronological order, in billions of years before present, AKA BYBP) 0.1, 1.1, 1.2, 1.7, 2.7, 2.9, 3.1, 3.5, 3.7, 3.8, and two at 4.0 BYBP. All but one of those predate complex life on Earth. The Earth is a dynamic world. This is excellent news from the perspective of continued habitability (vital elements are not getting locked away forever) but it’s not so good for preserving evidence. In fact, there’s a vast span of time, up to a billion years of the first years of our planet, where little to no geological evidence would survive. Evidence of those visits in 1.1, 1.2, and maybe 1.7 BYBP could be victims of the Great Unconformity. As for the older visits, possibly in 2.7 to 4.0 BYBP, there was ample opportunity for any artifacts to be subducted, consumed by chemical reactions, or simply buried under a kilometer of lava during a flood basalt event1. Much the same objections apply to other planets and minor planets. Even the Moon, generally spoken of as a dead, eternally static world, is thoroughly “gardened” by a constant hail of micrometeors slamming into regolith at interplanetary speeds. Estimates of how long human artifacts will survive on the Lunar surface range up to 100 million years. That’s a very long time in human terms, but do note that evidence of all but the very latest of the hypothetical visitors would have been gardened away. Nevertheless, the Moon is conveniently next door and there is a logical place to look for artifacts. The permanently shadowed craters at the Lunar poles sequester light elements visitors might want to exploit2. Even better, those craters have been shadowed for billions of years. Shackleton crater, for example, has been at the pole for at least two billion years. If the artifacts of the most recent four visitors were buried deep enough to escape gardening, they might survive. What we need is somewhere artifacts can plausibly survive for billions of years. The asteroid belt might be a decent bet, since its continued existence argues that objects can remain there for billions of years. It wouldn’t be terribly surprising if the first alien artifact to turn up turned up in the main belt. Ideally, we need some sort of Solar oubliette, where crap accumulates without being destroyed in the process and has done so for most of the Solar System’s history. Happily, as you might guess from the fact this essay was written at all, the Solar System does have at least one of those. Two, actually. From an artifact preservation perspective, Jupiter might seem a dismal prospect. Jupiter itself is insanely dynamic, not to mention being bereft of any solid surfaces. Its moons are likewise subject to history-erasing processes. Surely, maybe some alien wrench got lucky and didn’t aerobrake into Jupiter, lithobrake on a moon, or get ejected, but how would you find it amid all the crap orbiting Jupiter? To quote Wikipedia, “the Lagrange points (/ləˈɡrɑːndʒ/), also called the Lagrangian points or libration points, are points of equilibrium for small-mass objects under the gravitational influence of two massive orbiting bodies.” Jupiter is massive. The Sun is massive. It follows that there should be Sun-Jupiter Lagrange points, which there are. It also follows that objects perturbed into the Sun-Jupiter L4 or L5 could stay there for a very long time. Unsurprisingly, both the L4 and L5 regions3 are populated. There are 9,694 known Jupiter trojans4 at L4 and 5,628 at L5, but estimates suggest there could be a million 1 km+ diameter trojans. Even more intriguingly, some estimates suggest that some of those trojans have been trojans for a very, very long time. As in billions of years. As in, Jupiter’s trojans have been hoovering up garbage from across the Solar System for most of the life of the Solar System. As you know, middens are a great place to commit archaeology and here we have a cosmic midden. Two cosmic middens. Of course, both the main belt and Jupiter’s trojans occupy vast volumes. Poking through them would be expensive and time-consuming, but quite possibly rewarding. Even negative results would have interesting implications. All we need is a hundred billion dollars or so to fund a thorough search. Is it Kickstarter time? Or would BackerKit be better?5 Assuming that “artifact” is the correct word. If the evidence is biological, if say the aliens were careless while dumping their toilets, then its descendants could be with us today. They could be us. Imagine the honour of being descended from a galaxy-spanning civilization’s fecal bacteria! ︎“But what about all the Lunar helium-three?” some might ask. My response is too vulgar to be printed. Beings stupid enough to fall for the helium-three nonsense won’t build starships. ︎They’re only points in an ideal three-body situation. Once you add more bodies, Lagrange points become more like volumes. ︎L4 and L5 asteroids are named for heroes of the Trojan war. ︎Can I buy space probes on Etsy? ︎The post Where to Look for Evidence of Alien Visitors to Our Solar System appeared first on Reactor.