Accordingto Hollywood, Earth is surely one of the galaxy's "top places to visitbefore you die." Cinema aliens come here often enough that the StateDepartment should probably set up passport control.
Of course,that's fiction. But in the last hundred years, Homo sapiens has beenflamboyantly belching clues into space that could alert technically savvyextraterrestrials of our presence. Radarand television, odd chemical compounds in the atmosphere, and even theoccasional spacecraft sent beyond the heliopause are all messages in bottlesthat could conceivably wash up on the shores of ET's planet.
When Ipoint this out in talks, a frequent reaction is "Won't they come here andkill us?" I offer this response as proof of the general optimism of 21stcentury humankind.
Nonetheless,maybe this dystopian view is worth considering. Would the extraterrestrialscome here — if not to kill us — then to take our resources or compromise ourvirtue?
The answer,of course, falls within the discipline of alien sociology — a field in whichthe data are, shall we say, sparse. Indeed, since we have no idea what themores or motivations of extraterrestrials might be, you might conclude that,really, there's nothing we can say about whether the aliens would come here ornot.
But there'san alternative to this "know-nothing" approach. Let's consider whatmight conceivably encourage visits by those who've learned that humans arestrutting and fretting upon Earth's stage. After all, we've unraveled a fewthings about astronomy and physics, if not much about alien comportment.
Taking ourcue from Tinseltown, I note that most cineplexsentients come to Earth either to solve some sort of ugly reproductivecrisis or simply to take over the planet. The former doesn't make any sensewhatsoever. You can't breed with creatures at the zoo, despite the fact thatmost of the base pairs in the inmates' DNA are identical to yours (note thatthis is a biological incompatibility, and not just zoo regulations). Thealiens, needless to say, will have a different biochemistry, and probably noDNA at all. Forget, if you can, the breeding experiments.
Taking overthe planet would only make sense if there were something really special aboutour world. The best guess of the exoplanet specialists is that the number ofEarth-size planets in our galaxy exceeds tens of billions. That doesn't soundlike our hunk of real estate is terribly privileged.
They won'tcome here to mine our minerals, either. The entire universe is built of thesame stuff, and while the solar system has a higher percentage of heavyelements than found in many stellar realms, it turns out that this is preciselythe condition that seems to foster planet formation. In other words, ET's ownsolar system will be similarly blessed with these useful materials. So whywould they come here and incur multi-light-year transport charges?
Colonization?A hunt for additional living space? If the former is something aliens do, thenthey won't wait to hear from us before doing it. The British, after all, didn'tbegin their colonization of Australia because they had intercepted someaboriginal communications.
As forgetting a bit of lebensraum, well, planets are not great new habitat,because they're spheres. They're cursed with the minimum surface area for theirmass. As pointed out three decades ago by Gerry O'Neill, it's both moreefficient and enormously cheaper to build artificial habitats in your home starsystem.
OK, youargue, but Earth is more than just a handy source of gold or molybdenum, morethan merely random cosmic acreage aching to be invaded and subdued. It's anexceptional habitat for life. Water, oceans ? it's so gosh-darn good, it'spositively rare. The aliens will find our world lovable because it's livable.
Well, thatdoesn't pass the smell test, either. If the type of world that can support lifeis rare, then you don't have to worry about nearby extraterrestrials. Therewon't be any.
Othersuggestions about why they might visit include forestalling competition in theMilky Way marketplace, proselytizing, or just learning more about us. It's notclear that any of these goals requires "killing us," of course, butthe logic is wobbly anyway. Any beings that actually could come herewill be far beyond us in technological accomplishment. Imagine if you couldvisit the Neanderthals. Would you worry about commercial competition? Would yougive them bibles? Remember: these are (nearly) the same species as you are. Thealiens won't be. I dare say you wouldn't try convincing porpoises to join yourchurch.
Then again,there's that last point: they just want to learn more about us. Well, perhapsso. Maybe that's really what's interesting about Homo sapiens. Notgrabbing our habitat, saving our souls (or our environment), or subverting ourindustrial output — but assaying our culture. I'm willing to consider that evenvery advanced beings might find our culture mildly worthy of study.
Keep inmind that if they're near enough to find us, that implies that there are many,many galactic societies (otherwise the distances between any two of them will beenormous). If there are lots of them, then we're just another entry in abig book. Once again, not all that special. Kind of like another weird fishfound in the Atlantic. I don't expect mammoth expeditions to be sent our way.
But in anycase, if they do pick up our TV signals — or even bother to get in touch — thenthey can study our society from home. It's a lot cheaper and a lot faster thanbridging the light-years.
I guess theState Department doesn't need to set up that passport control.
- Video Player: Listening for Life
- Video Player: Reflections on Fermi's Paradox
- SETI at SPACE.com
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Seth Shostak is an astronomer at the SETI (Search for Extraterrestrial Intelligence) Institute in Mountain View, California, who places a high priority on communicating science to the public. In addition to his many academic papers, Seth has published hundreds of popular science articles, and not just for Space.com; he makes regular contributions to NBC News MACH, for example. Seth has also co-authored a college textbook on astrobiology and written three popular science books on SETI, including "Confessions of an Alien Hunter" (National Geographic, 2009). In addition, Seth ahosts the SETI Institute's weekly radio show, "Big Picture Science."