Everything about ‘Oumuamua is weird. Its nonspherical shape is weird. (Look around: you see any pancakeshaped planets or asteroids?)
HAVE WE SEEN OUR FIRST ALIEN PROBE?
BUT EVERYTHING ABOUT ‘OUMUAMUA IS WEIRD. — COLBY COSH
Itook some time this week to read up on ‘Oumuamua, the first object of interstellar origin to have been spotted in our solar system. ‘Oumuamua was discovered in 2017 and was photographed by telescopes and other instruments around the world as it zoomed close to the sun and shot off back into the void. You have probably seen an artist’s rendition of the object looking like a cigar, or, if we’re being honest, a turd.
The object is so small that its shape can’t be photographed directly: on every “camera” powerful enough to spot it, it was a point source of light, like a star. But the “light curve” produced as the object tumbled and reflected solar light has been reinterpreted, and it’s now thought most likely that the interstellar voyager is disc-shaped and quite circular. One of the paradoxes of astronomy is that the shape of an object like ‘Oumuamua, although nobody actually knows of any other object like ‘Oumuamua, is easier to infer than its size. It could be anywhere from 100 metres long to a quarter-mile.
‘Oumuamua is back in the news because a renowned and respected astronomer, Harvard’s Avi Loeb, has published a book about the space pancake with the title Extraterrestrial. Loeb thinks that ‘Oumuamua shows evidence of design by some spacefaring civilization, and he is frustrated that his profession isn’t more excited about this possibility. In interviews, his annoyance can make him sound like a scientific codger who has been passed by, but he is only 58 and his place at the pinnacle of astronomy is (still) unchallenged. The view that ‘Oumuamua is a spacecraft is that of a small minority, but it is not exclusive to Loeb.
What I learned from my reading is that ‘Oumuamua was underappreciated when it first appeared before the eyes of us laymen as a cute astronomy story. The more you know about science, alas, the less you are inclined to read science stories in any general-interest newspaper or magazine. But among professional astronomers, the intellectual ripples from the space poo are nowhere near subsiding.
Astronomy’s inferential picture of the galaxy beyond the frontier of the solar system led everyone to expect, before ‘Oumuamua appeared, that any interstellar objects that swam into our neighbourhood would be overwhelmingly likely to be “rogue” comets from other solar systems. Telescopes have since observed a second interstellar messenger in our solar system, the comet 2I/ Borisov. Borisov, named for its Crimean discoverer, met traditional expectations so well as to be a bit boring.
But everything about ‘Oumuamua is weird. Its nonspherical shape is weird. (Look around: you see any pancake-shaped planets or asteroids?) If it were a comet, astronomers felt confident that they ought to have been able to detect the “outgassing” produced when it approached the sun and grew hotter. That’s what gives ordinary comets their tails. But ‘Oumuamua showed no indication of any outgassing activity.
Nine months after its closest approach to the sun, ‘Oumuamua delivered its final surprise: it began to accelerate just a smidgen. This “non-gravitational acceleration” is, for Loeb, the clincher for possible intelligent-alien origin. Outgassing can make bodies in free fall accelerate, so astrophysicists were forced to choose between “the space pancake is outgassing, but we couldn’t detect it” and “uhhh, we’ll get back to you.” ‘Oumuamua’s seemingly stable rotation was a strike against option one, and early nonloebian explanations for its composition (is it a fragment of a destroyed planet?) seem to have problems.
The tension between Loeb and other astronomers, as far as I can understand it, seems somewhat philosophical at root. The natural response of most astronomers to the bizarre appearance of ‘Oumuamua was to look for weak assumptions about the nature of far outer space that might be mistaken. If we expected a comet and got a pancake, our expectations were probably wrong.
Humans haven’t visited extrasolar space, and almost all of what they know about its composition comes from statistical modelling and simulations. Loeb would say that the hypothesis that there are aliens in our galaxy has a nonzero probability, and should feature somewhere in the calculations.
His mainstream opponents would appeal to the same methodological naturalism that leads science to rule out “God made ‘Oumuamua and threw it at us, but just missed.” They would say they have to work really, really, really hard, and for a long time, before introducing an alien-engineer hypothesis.
Loeb thinks that ruling aliens out prematurely creates the danger that we will accept a contrived, misleading second-best physical explanation — and then perhaps build further mistakes on that explanation. All a lay observer can say for sure is that Loeb is clearly not crazy: aliens don’t quite belong in the deus-ex-machina bin along with purely supernatural explanations.
Plans are underway to build a scientific infrastructure for detecting more nearby interstellar visitors to put in the catalogue alongside 1I (’Oumuamua) and 2I (Borisov). Soon we’ll know which kind of starry messenger is more common: maybe our galactic neighbourhood is full of reddish self-propelled space pancakes, and there’s an easy explanation for where they come from. Or maybe the universe changed in 2017 and we just don’t know it yet.