Basic AssumptionsIf an incoming alien race has faster than light travel, teleportation, reactionless drives, direct conversion of matter to energy, anti-gravity, cloaking devices, tractor beams, force fields or other staple science fiction technologies, all bets are off. We have no idea what they'd be able to do because we have no idea how those technologies could even be possible, given our understanding of the laws of physics. And if you're about to pooh-pooh that as impossibly myopic, why not first prove you know anything about the laws of physics? Say, explain how Trojan orbits work, in detail, as in, do the math. Or explain how Maxwell's Equations lead to radio. Or tell us how Noether's Theorem relates the structure of the Universe to conservation of energy and momentum.
We can assume that any race capable of crossing interstellar space will be able to do anything we can do or even remotely contemplate doing. On the other hand, space travel won't be trivial, even for them. Traveling between ships in their fleet will probably be easy out there in zero gravity, but getting to speeds capable of crossing space in a reasonable time, and slowing down once they reach their destination, will take serious effort. Any civilization capable of crossing interstellar space will probably be able to travel freely between planets, but it will still take a lot of energy and time. Landing on massive planets, and getting off again, will also be a significant effort. Terraforming planets will likewise take a lot of effort and, even more important, time. We can't assume that they'll be limited by our limitations, but they will probably try to be as efficient as possible.
If Earth-like planets are extremely rare and we just happen to be on one that the aliens need, well, sucks to be us. On the other hand, if earth-like planets are at all common, the odds are very much against one of them having an intelligent civilization. If humans last 5 million years, that will be about 1/1000 of the age of the earth. The odds of aliens coming here during our window of existence are about 1/1000. Similarly, there should be 1000 planets without intelligence for every one with it.
So we'd have to assume that any extra-solar visitors come to our solar system for a specific reason, which might be to colonize, gather resources, or explore. (Or possibly, as in Arthur C. Clarke's Rama novels, simply to use the Sun for a trajectory change.) We should pretty much assume that they are ahead of us technologically in just about everything. Anything we have on the drawing boards, they can do.
They certainly will have technology for observing planets around other stars, since we ourselves have begun to do it. If they have telescopes millions of kilometers apart flying in formation with their ships, they can combine the images to obtain the effective resolution of a telescope millions of kilometers in diameter. We already have conceptual ideas for doing this. So quite likely they would have pretty good images of all the planets in our solar system.
If they pick up our radio and television signals, they'd probably know that there is at least that level of technology in our solar system. Most likely they'd pick up only the carrier wave, with the actual signal information too weak to pick out. Then again, in zero gravity, there would be nothing to stop them from building a radio dish kilometers across. We have to assume they are at least as good at cryptography as we are (and we are - no brag, just fact - pretty darned good), so if they could pick up the information, they would likely be able to decipher it.
ResourcesIn the unlikely event they simply come here blind because they just picked a G-class star at random and didn't do any reconnaissance on the way in, it's very likely that they wouldn't lightly pack up and go to another star, since interstellar travel will be resource and time intensive. And, of course, if they know what's here, then they came here for a specific reason. But if their primary goal is resources, and they can travel easily between planets, there are much better sources than the Earth.
- Water: Icy moons are every bit as convenient as Earth as sources of water. Comets are probably too small and widely scattered to be of much use, although a single comet can supply many cubic kilometers of water. But icy moons are a lot easier to land and take off from than something as massive as Earth. Of course, there's still the gravity of the parent planet to deal with. But Kuiper Belt objects will be icy and will present minimal gravity problems.
- Metals: Nickel-iron asteroids can supply far more metal than our iron mines, with the added advantage that the smelting is mostly already done. Rarer metals can be extracted during the refining of nickel and iron, just as we do on Earth. Asteroids and comets have the added advantage of negligible gravity.
- Oxygen: Obtain it by electrolyzing water, or as a by-product of smelting silicates.
- Hydrocarbons: Assuming they use hydrocarbons for some energy needs or a base for creating other organic chemicals, why drill on Earth when there's a whole planet full of it at Jupiter, and lakes of hydrocarbons on Titan?
- Energy: Pave Mercury with solar panels, or simply build vast arrays in space. Use the harvested energy to fabricate still more panels, as well as whatever else you need. Build a concave mirror kilometers across and use sunlight to smelt metals out of asteroids.
We are also unlikely to have anything cultural or technological that they need. Iron and steel? With nickel-iron asteroids for the taking? Electronics? They probably maxed out Moore's Law ages ago. Some of our cultural artifacts and art works may be of interest to xeno-anthropologists. As for our cultural knowledge, they pick up our wireless Internet and shluurrp!
So Who Needs Earth?There are a few reasons why extraterrestrial visitors might come specifically to Earth apart from curiosity or exchanging greetings:
- Hydrothermal Ores: The problem with using the Moon or asteroids as sources of minerals is that a lot of our ores on earth involve water in some way. Copper, zinc and lead are mostly deposited by hot solutions. Aluminum is concentrated by weathering of aluminum rich rocks in tropical environments. Those deposits might make terrestrial sources more attractive than extraterrestrial ones.
- Lithophile elements: Plate tectonics and geochemical recycling have made the earth's interior more homogeneous and has concentrated certain elements in the crust. These tend to be atoms with very large or very small ionic radii, high ionic charges, or both. Things like lithium, beryllium, boron, uranium, thorium, cesium, and rare earths might be easier to extract from Earth rocks than asteroids. We now know that planets abound, but watery earth-like planets may not be so common.
- Organic chemicals: If you want complex organic chemicals, it might be easier to harvest them from the biosphere rather than synthesize them from scratch. Maybe we have things they didn't know about. Most interesting this - what do you call it? - cocaine.
- Convenient Working Environment: If you're an oxygen breather with human-like environmental needs, it may be a heck of a lot easier to land on Earth and do things than terraform Venus or build gigantic domes on the Moon.
- R & R: No matter how big your starship is, even if it's got holodecks, it has to get boring after a while. If they can survive on Earth, they'll very likely want to come down for some breathing room and to see new scenery.
- A Place to Live: Bad news. There have to be lots of
Earth-like planets without intelligent life. After all, Earth was like that
for over 99.9% of its history. So why pick Earth? Assuming they didn't come
here just because they enjoy destroying other intelligent life forms,
something probably went very wrong. Either we're the nearest Earthlike
planet and they need it very badly, or they didn't know we were here, or
we're so far below their level we don't rate as intelligent.
If their life support is failing and there are twenty billion of them, we're toast. But if there aren't too many, and they're willing to work with us, we could probably find some open spaces for them while they terraform Mars or Venus.
They Come and GoThey come into the solar system, harvest a few comets and metal rich asteroids, suck hydrocarbons out of the Gas Giants, unfurl giant solar arrays to replenish their energy storage, and leave without contacting us at all. If this had happened even in 1900, we probably would have not even noticed it, but today we would. We'd certainly know we weren't alone, but on the other hand we'd be more alone than ever, since there are races that travel among the stars and don't even consider us worth contacting.
We are SuperiorForget this. They came here. We can't go there. They will likely be ahead of us in everything. The only exception might be a District 9 scenario, where a small alien contingent arrives, either as refugees or because they had a catastrophic failure of their ship.
We're OK, They're OK (Star Trek)The best of all possible universes. But we'll still be grossly inferior to them in technology. But they'll treat us nice, and maybe let us share their stuff. That may not be a good thing (see Culture Shock, below).
The Prime DirectiveMaybe they come for research. They're cataloging and mapping solar systems and alien civilizations (to them, we're the aliens). Maybe they simply show up openly, like explorers of centuries past did to isolated societies. But that's an open invitation to all sorts of unpredictable complications. Regardless of their final intentions, the sensible approach would be to observe us clandestinely first. Given our ability to ping radar signals off other planets, they'd want to keep out of range.
If they'd done this in 1900, it would be a piece of cake in one way and far more difficult in others. They'd be able to approach earth and even land with no fear of detection, but they would have to gather information painstakingly slowly. Today, they'd have to keep a wide berth and be extremely circumspect, but between our wireless Internet and media, they'd have torrents of information coming in.
It's virtually impossible that aliens would be able to travel undetected on Earth. In one of his early drafts of 2001, Arthur C. Clarke envisioned there were thousands of humanoid species, of whom a small fraction might be mistaken for humans at a distance. Only a handful could pass for humans close up and none at all could pass even the simplest physical exam. But given our progress in robotics, it seems very likely aliens could build passable robotic replicas that could interact with humans.
It's getting them to Earth that's the dicey part. We can detect asteroids 100 yards across, and any incoming ship of any size that displayed inexplicable changes in course would be obvious. They certainly wouldn't be able to just waltz in and settle into orbit. NORAD would be all over it. Maybe they could come in from the direction of the sun or from behind the moon and evade detection most of the way, but getting an alien ship to Earth undetected would be tricky. Stealth technology might be a big help. Our mutual mistrust might also be an assist. They could masquerade as a clandestine mission from some terrestrial power.
War of the Worlds (or V, or the Borg)We're food, raw material, or an impediment. Maybe we can make ourselves enough of a nuisance that they leave us alone if we stay out of their way. On the other hand, with our industrial base gone, we're back to rocks and sharp sticks pretty soon, and what kind of a fight can we put up then?
We might make a good ad hoc food source, especially as a way of exterminating us, but we'd be lousy as a continuing source of food. We escape, attack our handlers, and grow slowly. As opposed to cows, who are dumb, docile, fast growing and capable of eating grass.
Watership DownWatership Down was a 1972 novel by Richard Adams about a colony of rabbits that had to find a new home. It begins with a vision of bulldozers tearing up the field the rabbits lived in. The humans didn't hate the rabbits, or even care about them. They were just in the way.
I consider this the most likely scenario. They come to Earth because they want copper and aluminum, and they need open space to set up facilities to fabricate things for their ships, and why build a huge enclosed dome on the Moon when Earth already has a comfortable working environment? So they see our copper mines and strip them out. They detect other hydrothermal ores forming underground and dig them out, as well. And they don't care that it's Yellowstone National Park. Maybe they'll realize we already have a lot of refined copper and root it out of our cities, just like the Spanish plundered New World silver. They don't hate us, and they may even try to avoid gratuitous harm, but in comparison to them, we're about as smart as a Labrador retriever or a hamster, and we just don't rate on their scale. Some of them might study us as exercises in exobiology, but their children can write things more advanced than Hamlet and make up songs more elaborate than anything by Beethoven. Our art will interest them less than the cheapest tourist trinket impresses us. They won't go out of their way to hurt us, because advanced beings don't unnecessarily mistreat lower life forms (although kids will step on bugs), but if they want something, they'll take it. If they want to clear Florida to build a solar power array, or use Iowa to grow some crop important to them, they'll do it. We'll just have to move, just like the bunny rabbits did.
Culture ShockMaybe benevolent aliens won't be such a good thing after all. Even when advanced civilizations have encountered primitive ones on earth peacefully, the results have generally been rough on the primitive civilization.
For openers, what's the point of research when the aliens already have the answer to any question we might ever ask? We could easily become passive users of their knowledge.
Then there's the impact on our beliefs. If they have indisputably been around for millions of years, that pretty much demolishes a recent creation, right? Or maybe not. It's very likely we'd see the rise of powerful movements denouncing the aliens as liars or hoaxers and demanding an end to contact with them. What if they've had a peaceful, benign, just civilization for hundreds of thousands of years, superior to us in every way, and have never, ever had the concept of a god? What if they have an extremely dogmatic religion, especially one that meshes with some of our more dogmatic creeds? What if they have rigid sex roles, or rigid social classes, or practice slavery? What if they have no limits on sexual behavior whatsoever?
Finally, some humans will certainly interact more closely with the aliens than others. If the aliens aren't careful, they can create such an economic disparity that humanity ends up becoming a wholly owned subsidiary of Aliens, Inc. Even on earth, anthropologists have noted there are clearly defined zones of influence around outposts of advanced civilizations. Some humans would be almost wholly assimilated. Others would find that proximity to alien knowledge gives them powerful advantages over less favored humans, either in trade or in the use of force.
That assumes that the aliens are benign or at least neutral. If they're here to exploit us or at least get what they want without regard for us, then things will get a whole lot nastier. Because there will certainly be humans who will work for whatever rewards the aliens offer. They'll strip-mine Chicago for the metals, in exchange for power or sex. Or they'll act as overseers to keep the rest of us in line.
It's entirely possible that aliens will be so different from humans that neither will find the other very interesting. They're physically unattractive, their sexual customs are unappealing. Not horrifying, just unappealing. Their philosophy is based on categories we find unintelligible. Their music is based on some oddball 11-tone scale. Their religion revolves around deities who preside over things we find utterly irrelevant. Their physiology is different enough that their sports strike us as pointless. Their literature describes customs and institutions we don't care about. We can understand them perfectly - we just don't find anything about them appealing or interesting. Sure, their biochemistry, biology and knowledge of other planets will be interesting, but everything about them is shades of gray and beige. And we look the same to them.