Nobody knows what ‘Oumuamua was, this object that passed through our inner solar system in late 2017, but also and more notably, nobody can say much about what it was not. Avi Loeb, the chair of Harvard’s astronomy department, argued in a paper and now in a long interview with Haaretz that it could have been a manufactured item, a spaceship or a solar sail, originating from some alien civilization. No one will ever track down ‘Oumuamua to settle the question, but the purpose of Loeb’s argument was to be unsettling—to demonstrate that being the chair of Harvard’s astronomy department no longer means rejecting the possibility of alien technology, that when ‘Oumuamua departed, it carried away with it a whole set of presumptions that had been operating under the guise of conclusions.
Whatever else it may have been, ‘Oumuamua was an echo or reflection of the now long-abandoned Project Daedalus, an actual answer coming inbound where a hypothetical question had once been outbound. Project Daedalus was the nearest possible leap into interstellar existence when I was a child, a proposed spacecraft floating moodily in glossy magazine renderings.
We had only one exoplanet, then. One! In the entire universe. At most. The sum of our known realm of planets was nine here, around our Sun, and one over there, six light-years away, orbiting a dim little thing called Barnard’s Star and causing it to wobble. The name “Barnard’s Star” still carries a thrill when I say it in my mind; that was the name of the frontier of possibility. And the frontier of non-impossibility: scientists could imagine a spacecraft that could get there, without warp drives or cryo-suspension chambers or any other fantastic ways to get around the laws of physics or biology. Daedalus was (or was going to be, or could have been going to be) a cluster of globular tanks and a funnel, nuclear-powered, built in space near our own planet and sent off, at a reasonably small fraction of light speed, to go somewhere else. I gazed at the renderings and drew globular tank-clusters and nuclear-drive funnels on sketch paper, alongside assorted starfighters and ray guns and space-adventure stuff.
There wasn’t really any chance there’d be aliens flying starfighters around Barnard’s Star. Aliens were either paranormal woo-woo or fantasy. And owing to the limits of planet-detection theory, the planet there, the only known planet in the rest of our universe, had to be somewhere in the size range of Jupiter, and as close to its sun as Mercury, combining the deadest features of two dead planets.
But the alternative, at the time, was total aloneness. There were eight lifeless planets around us—we’d learned enough about Mars to write it off; no four-armed green swordsmen would ever fight John Carter—and beyond that we knew of nothing else. Space belonged to science, and science couldn’t see a thing out there but stars and nebulae and other huge objects scattered in the void. And if science couldn’t see a thing, it was unreasonable to guess it might be there. To the best of our knowledge, it wasn’t.
For a while, things were even lonelier. Project Daedalus never got past the idea stage. The evidence for the presence of the Barnard’s Star planet got reexamined, and astronomers concluded it had never really been there at all.
People kept looking, though, and other stars began to show themselves wobbling and dimming in ways that couldn’t be explained away. A new planet was confirmed, then another, a handful—dozens—scores—and then the Kepler space observatory was launched, and they began stacking up by the hundreds. Nor were they just big-and-close Jupiter-style planets, but came in an assortment of sizes and distances, including effectively Earth-size and Earth-distance.
Late last year, the exoplanet hunters reported there was one orbiting Barnard’s Star, after all—not a giant, but a “super-Earth,” estimated at 3.2 times our planet’s mass, and probably frozen.
All along, the question of how to think about alien life had depended on larger framing questions: How unusual is Earth? How unusual is life on Earth? From the immediate, narrow evidence of our own solar system, the conservative answer seemed to be that there was nothing else like it. Life was fragile, and the conditions to support it were hard to find.
But those premises were shifting, too, closer to home. Jupiter or Saturn had nothing about them that could possibly support life, but then space probes got a look at moons around them that appeared to have liquid water under icy crusts. What if a habitable moon was enough? Meanwhile, the ocean bottoms of Earth itself—cut off entirely from life-giving sunlight, and assumed to be cold and dead—were teeming with living things around geothermal vents.
At some point, as the empty spaces near and far filled up, the safe guess of a lonely universe stopped seeming safe. Loeb told Haaretz:
Anyone who claims that we are unique and special is guilty of arrogance. My premise is cosmic modesty. Today, thanks to the Kepler Space Telescope, we know that there are more planets like Earth than there are grains of sand on all the shores of all the seas.
The more we know, the more we know we don’t know. ‘Oumuamua entered our solar system from a direction nothing else had entered it from, at a speed nothing else had arrived at, with a shape nothing else had ever had. It accelerated, by some means no one had ever previously observed, and went away. Whether it came from a technosphere built by aliens was almost beside the point, or too narrow a question: what is certain is that there is at least one thing of its kind in the universe, which is infinitely more things of that kind that we knew existed in the universe two years ago.