It is part of the human experience to slowly realize we are each an isolated mind in a sea of other isolated minds, and then to spend our lives trying to cross the mighty gulfs between ourselves and others, striving to make a connection. Everybody wants to be found. So it’s natural, as our science has progressed, that the human race should project its collective hopes onto the cosmos and see if anyone else is reaching out to us. The last century is permeated with science fiction of alien visitors, and the search for extraterrestrial intelligence (or SETI) is the manifestation of our hopes that someone out there is trying to find us. So great is our desire for contact, we instinctually see aliens in emissions of radiation, in planetary landscapes, and in comets on hyperbolic trajectories. In a sense, we anthropomorphize the universe.
Ascribing human characteristics or motives to natural objects is nothing new. What science has done is to set a grander stage for our anthropomorphizations. We have seen faces in vegetables and toast and mountainsides for millennia, and a quick search for “pareidolia” will reward the reader with examples. But it took the Viking mission for us to see a face on Mars. For ages, people have heard voices calling to them in the wind, even from the northern lights. Is it surprising that when astronomers Jocelyn Bell Burnell and Antony Hewish heard periodic radio emissions from a pulsar for the first time in 1967, they named the phenomenon LGM-1, for Little Green Men?
We interpret shadows on a curtain, or a tapping branch at the window, as the arrival of a visitor. So it was in 2016, when our minds leapt to the thoughts of “alien megastructures” when it was discovered that the face of Boyajian’s star was intermittently veiled. We now know, however, that what shadowed the star was simply clouds of dust. Eventually, thanks to the scientific method, the actual causes for these surprising discoveries get sorted out, but science’s initial impact is to grant our imaginations new vistas to run wild.
The latest example is that of ‘Oumuamua, the first interstellar object found among our planets. This asteroidal or cometary object, barely bigger than a city block, has been quickly passing through the solar system for the past many years. It made its closest approach to the sun on Sept. 9, 2017, but was discovered by the Pan-STARRS1 telescopic survey only on Oct. 17, 2017, just after it passed a mere 63 Earth-moon distances from us. Even at this closest approach to Earth, ‘Oumuamua was far dimmer than even distant Pluto appears to us. After a few months it was too far to be observed at all. Already it’s at the orbit of Saturn , moving far faster than any object bound to the sun’s gravity.
The way it reflected sunlight over time suggested it was a very elongated, perhaps pancake- or cigar-shaped object, spinning and tumbling every eight hours or so. The interstellar origin and the possible cigarlike shape of ‘Oumuamua instantly recalled Arthur C. Clarke’s novel Rendezvous With Rama, in which humans explore a cylindrical alien spacecraft passing through our solar system. This has framed the mystery of ‘Oumuamua ever since, culminating in a November article by Abraham Loeb of Harvard titled “6 Strange Facts About the Interstellar Visitor ‘Oumuamua,” which has received recent press.
The strange facts are as follows. Telescopes like Pan-STARRS on Haleakalā in Hawaii, with the ability to detect objects like ‘Oumuamua, have been operational only in the past decade. Some calculations suggest that the natural ejection of asteroids from other solar systems should be too rare for us to happen to spot even one interstellar asteroid in the few years since we’ve gained the ability to see them. The velocity of ‘Oumuamua when it entered the solar system is also unusual and in some sense too slow to easily reconcile with ejection from another stellar system. ‘Oumuamua’s shape is more elongated than any solar system object, a challenge to explain. ‘Oumuamua put off no detectable infrared radiation, implying it is very small; some calculations suggest it would have to be unusually reflective to be seen at all. Strangest of all is the fact that ‘Oumuamua is not simply orbiting the sun on a ballistic trajectory—it is receiving small but definite thrusts. Comets receive thrusts, too, as ice sublimates on their surfaces and shoots off as gas, like a rocket. But no gases or dust were detected around ‘Oumuamua. Loeb and colleagues suggest it is responding to sunlight in the same way as an advanced spacecraft design called a solar sail, using the sun’s radiation like a sailboat uses the wind.
And yet. Other calculations suggest ejection of asteroids from other stars’ asteroid belts should be so common that the real mystery is why we haven’t found more. ‘Oumuamua’s elongated shape has many plausible explanations. One intriguing possibility is that fast passage through an interstellar dust cloud—which would have “sandblasted” it—could have slowed it down in a way that makes more sense of its velocity as well as explains why there aren’t more such objects. More refined calculations have shown that ‘Oumuamua is exactly as reflective as asteroids and comets we’re familiar with. And even though no gases were seen jetting off ‘Oumuamua, we can only rule out some gases, and that list doesn’t include the most likely gas of all, water vapor from sublimating ice, which may yet contribute to its thrust. In fact, if it were a solar sail, the tumbling rotation of ‘Oumuamua would have prevented it from converting sunlight and solar wind into thrust. Almost certainly, ‘Oumuamua is simply the latest object onto which we have pareidoliacally projected our hopes and desires.
As science continues to provide us more inkblot tests like ‘Oumuamua, the scientific method will continue to help us make sense of what we’re seeing. As an astronomer, I’m grateful for that objective process. But it doesn’t mean we should subordinate imagination to science. It wouldn’t even make sense to try: The scientific method can only test hypotheses, and someone has to first imagine those possible hypotheses. As long as we’re testing the more prosaic and likely explanations, such as asteroids and comets, it does no harm while we’re at it to test the interstellar spacecraft hypothesis through a responsible peer-reviewed scientific process. The greater harm might be to have the evidence of alien contact in front of us someday but fail to see it because we didn’t dare to imagine the question. In any case, it’s obvious that many scientists long for the nonprosaic explanation. The name ‘Oumuamua is Hawaiian for scout, and planetary astronomer Andy Rivkin has written and performed a lovely song full of longing to get to know our interstellar visitor. It’s such an integral part of the human experience to long for contact, to see faces in inanimate objects. The world would be less wonderful if human scientists didn’t also sometimes help us all anthropomorphize the cosmos.