Extraterrestrial: The First Sign of Intelligent Life Beyond Earth

by Avi Loeb

What we see when we bother to look up has inspired humanity for as far back as recorded history. Indeed, it has recently been surmised that forty-thousand-year-old cave paintings throughout Europe show that our distant ancestors tracked the stars. From poets to philosophers, theologians to scientists, we have found in the universe provocations for awe, action, and the advancement of civilization. It was the nascent field of astronomy, after all, that was the impetus for the scientific revolution of Nicolaus Copernicus, Galileo Galilei, and Isaac Newton that removed the Earth from the center of the physical universe. These scientists were not the first to advocate for a more self-deprecating view of our world, but unlike the philosophers and theologians who preceded them, they relied on a method of evidence-backed hypotheses that ever since has been the touchstone of human civilization’s advancement.

Are we, both scientists and laypeople, ready? Is human civilization ready to confront what follows our accepting the plausible conclusion, arrived at through evidence-backed hypotheses, that terrestrial life isn’t unique and perhaps not even particularly impressive? I fear the answer is no, and that prevailing prejudice is a cause for concern.

Over the years, I have come to believe that the laws of physics cease to apply in only two places: singularities and Hollywood. Personally, I do not enjoy science fiction when it violates the laws of physics; I like science and I like fiction but only when they are honest, without pretensions. Professionally, I worry that sensationalized depictions of aliens have led to a popular and scientific culture in which it is acceptable to laugh off many serious discussions of alien life even when the evidence clearly indicates that this is a topic worthy of discussion; indeed, one that we ought to be discussing now more than ever.

But our planet’s scientific community and the public would come to know it simply as ‘Oumuamua—a Hawaiian name reflecting the geographical location of the telescope used to discover the object.

Among Hawaii’s state-of-the-art telescopes are the ones that make up the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS), a network of telescopes and high-definition cameras located at an observatory atop Haleakala, the dormant volcano that forms most of the island of Maui. One of the telescopes, Pan-STARRS1, has the highest-definition camera on the planet, and since it came online, the system overall has discovered most of the near-Earth comets and asteroids found in the solar system. But Pan-STARRS has another distinction—it gathered the data that initially tipped us off to ‘Oumuamua’s existence. On October 19, astronomer Robert Weryk at the Haleakala Observatory discovered ‘Oumuamua in the data collected by the Pan-STARRS telescope, images that showed the object as a point of light speeding across the sky, moving too quickly to be bound by the Sun’s gravity. This clue quickly led the astronomy community to agree that Weryk had found the first interstellar object ever detected in our solar system.

The Hawaiian word ‘oumuamua (pronounced “oh moo ah moo ah”) is loosely translated as “scout.” In its announcement of the object’s official designation, the International Astronomical Union defined ‘oumuamua slightly differently, as “a messenger from afar arriving first.”

Interstellar visitors are far rarer than asteroids or comets. In fact, at the time of ‘Oumuamua’s discovery, we had never seen an object that originated outside of our solar system pass through it. This distinction was quickly lost. A second interstellar object was discovered shortly after ‘Oumuamua was identified, and in the future, we are likely to discover many more, particularly with the Vera C. Rubin Observatory’s upcoming Legacy Survey of Space and Time (LSST).

There is humility in following the evidence, and it frees you from preconceptions that can cloud observations and insight.

Our civilization has sent five man-made objects into interstellar space: Voyager 1 and Voyager 2, Pioneer 10 and Pioneer 11, and New Horizons.

And if other civilizations developed out there among the stars, wouldn’t they have felt that same urge to explore, to venture past familiar horizons in search of the new? Judging by human behavior, that would not be surprising in the least.

My subject was the habitability of the universe and the likelihood that in the coming decades, we would discover evidence of extraterrestrial life. And once we did, that discovery would force on humanity the appreciation that we’re not that special.

It is commonly thought that life is a collection of the places you visit. But this is an illusion. Life is a collection of events, and these are the results of choices, only some of which are ours to make.

It was also at this time that I started to realize that while philosophy asked the fundamental questions, it often couldn’t resolve them. Science, I was learning, might put me in a better position to pursue answers.

I have also found that staring out into the vastness of space, contemplating the start and end of everything, provides a framework for answering, “What is a life worth living?”

Over time, I have come to appreciate science slightly more than philosophy. Whereas philosophers spend a great deal of time inside their own heads, scientists are all about having a dialogue with the world. You ask nature a series of questions and listen carefully to the answers from experiments. When done frankly, it is a usefully humbling experience.

Science is like a detective story. For astrophysicists, this truism comes with a twist. No other field of scientific sleuthing confronts such a diversity of scales and concepts. Our chronological scope of inquiry starts before the Big Bang and stretches out to the end of time, even as we recognize that the very notions of time and space are relative. Our research descends to quarks and electrons, the smallest known particles; it reaches out to the edge of the universe; and it concerns—directly or indirectly—everything in between.

In fact, it is worth admitting up front that the likelihood of scientists ever obtaining demonstrative proof is very remote. Catching up to and photographing ‘Oumuamua is impossible. The data we have is all we will ever have, leaving us the task of hypothesizing explanations that fully account for the evidence. This is, of course, a thoroughly scientific undertaking. No one gets to invent new evidence, no one gets to ignore evidence that is at odds with a hypothesis, and no one gets to—as in the old cartoon of a scientist working through a complex equation—insert “and then a miracle happens.” Perhaps the most dangerous, most worrisome choice, however, would be declaring of ‘Oumuamua, Nothing to see here, time to move along, we’ve learned what we can and we’d best just go back to our old preoccupations. Unfortunately, as of this writing, that seems to be what many scientists have decided to do.

Its brightness as it rotated gave us vital clues about what ‘Oumuamua couldn’t look like and what it might look like. In the latter category, the object’s relatively small but extreme dimensions—with a length at least five to ten times greater than its width—allowed only two possible shapes. Our interstellar visitor was either elongated, like a cigar, or flat, like a pancake.

Either way, ‘Oumuamua was a rarity. If it was elongated, we had never seen any naturally occurring space object that size and that elongated; if it was flat, we had never seen any naturally occurring space object that size and that flat. Consider, for context, that all asteroids previously seen in the solar system had length-to-width ratios of, at most, three. ‘Oumuamua’s, as I have just noted, was somewhere between five and ten. And there was more. In addition to being small and oddly shaped, ‘Oumuamua was strangely luminous. Despite its diminutive size, as it passed the Sun and reflected the Sun’s light, ‘Oumuamua proved to be relatively bright, at least ten times more reflective than typical solar system asteroids or comets. If, as seems possible, ‘Oumuamua was a few times smaller than the upper limit of a few hundred yards that scientists presumed it to be, its reflectivity would approach unprecedented values—levels of brightness similar to a shiny metal.

As I have mentioned, when ‘Oumuamua sped part of the way around the Sun, its trajectory deviated from what was expected based on the Sun’s gravitational force alone. There was no obvious explanation for why.

Following a trial during which it is claimed his accusers refused to even look through his telescope, Galileo was found guilty of heresy. He spent the rest of his life, nearly a decade, under house arrest. Galileo was forced to abandon his data and discovery and recant his statement that the Earth circled the Sun, but legend has it that afterward, Galileo whispered under his breath, “And yet it moves.” The story is likely apocryphal, and even if it’s true, its truth is beside the point—or at least it was for poor Galileo. Consensus had won out over evidence.

At the time of this writing, the scientific community has coalesced around the hypothesis that ‘Oumuamua was a comet, albeit a peculiar one. A virtue of this hypothesis is its familiarity. We have observed many comets whose trajectories deviated from paths shaped by the Sun’s gravity alone. We also know why that happens: in all cases, it is due to outgassing. But as I have just explained, ‘Oumuamua showed no outgassing. And yet it deviated.

There is yet another difficulty with the outgassing-comet hypothesis, regardless of whether ‘Oumuamua outgassed pure hydrogen or not. Its acceleration during deviation was smooth and steady. Comets are ungainly rocks; their rough and irregular surfaces retain unevenly distributed ice. As the Sun melts the ice and the outgassing produces propulsion, it does so across that rough and pitted surface. The result is what you would expect—a herky-jerky acceleration. But that is not what we saw ‘Oumuamua do. In fact, it did the very opposite of that. The odds of a naturally occurring comet composed of 100 percent hydrogen ice that outgasses from one location producing smooth acceleration? About the same as the odds of natural geological processes producing a space shuttle. Moreover, to account for ‘Oumuamua’s degree of deviation, a statistically significant portion of its total mass would have had to be outgassed.

I have long been aware that within the discipline of astronomy, SETI faces hostility. And I have long found that hostility bizarre.

I take issue with the suspicion often visited on SETI. Compared to some flights of theoretical physics, the search elsewhere in the universe for something that is known to exist on Earth, the phenomenon of life, is a conservative line of inquiry. The Milky Way hosts tens of billions of Earth-size planets with surface temperatures similar to our own. Overall, about a quarter of our galaxy’s two hundred billion stars are orbited by planets that are habitable in the way Earth is, with surface conditions that allow liquid water and the chemistry of life as we know it. Given so many worlds—fifty billion in our own galaxy!—with similar life-friendly conditions, it’s very likely that intelligent organisms have evolved elsewhere. And that’s counting only habitable planets within the Milky Way. Adding all other galaxies in the observable volume of the universe increases the number of habitable planets to a zetta, or 1021—a figure greater than the number of grains of sand on all of the beaches on Earth. Some of the resistance to the search for extraterrestrial intelligence boils down to conservatism, which many scientists adopt in order to minimize the number of mistakes they make during their careers.

To say that my raising the possibility that ‘Oumuamua was artificial technology met with disapproval is putting the matter mildly. To be sure, the popular media was delighted, and the broader public was fascinated. But my fellow scientists were, shall we say, more circumspect. In July 2019 the ‘Oumuamua Team of the International Space Science Institute (ISSI) published their unambiguous conclusion in Nature Astronomy: “we find no compelling evidence to favor an alien explanation for ‘Oumuamua.” The immediately preceding paragraphs declared that the extraterrestrial-technology theory that Bialy and I had put forward was provocative but baseless.

Not long after the discovery of ‘Oumuamua, we encountered our second interstellar object. By the time you read this book, we may well have found others. This second interstellar object is named 2I/Borisov, after Gennadiy Borisov, a Russian engineer and amateur astronomer who on August 30, 2019, using a sixty-five-centimeter telescope of his own construction, identified the object in the skies above Crimea. And it was Borisov who first ascertained that its trajectory was hyperbolic. Just as had been true for ‘Oumuamua, 2I/Borisov was moving too fast to be gravitationally bound to the Sun. And so, just like ‘Oumuamua, 2I/Borisov had come from outside our solar system and was on a path that would send it through and beyond our solar system. But otherwise, 2I/Borisov was unremarkable. It was an interstellar comet, without question, and for this reason it was distinctive; any interstellar object is a rarity. But its distinctiveness ended there. Its coma and outgassing resembled our solar system’s comets’ in all characteristics; 2I/Borisov was icy and decidedly not exotic.

Perhaps long, long ago, ‘Oumuamua was not junk but extraterrestrial technological equipment built for a distinct purpose. Perhaps it was something closer in intent to a buoy.

To be sure, it would be transformative to learn what preceded the Big Bang, where the matter sucked into a black hole goes, or what theoretical insights finally square relativity with quantum physics. Indeed, I have devoted a significant portion of my life and career to answering the first two of these questions. But would the answers to these questions change our sense of ourselves as significantly as learning that we are just one intelligent species among many—or, conversely, that we are the only conscious intelligence to arise in the universe? I doubt it. Because I believe this question is so consequential, I find it remarkable how rarely, and how cavalierly, scientists have gone about seeking an answer. That didn’t start with the resistance to my lightsail theory; far from it. Scientists’ reluctance to read the messages of ‘Oumuamua long predates its passing through our solar system.

Unlike most equations, Drake’s was not designed to be solved. Rather, it was intended to serve as a framework for thinking about how many intelligent civilizations might occupy our universe.

Physics is a dialogue with nature, not a monologue.

Science is first and foremost a learning experience, one that works best by keeping us humble when we make mistakes, like children figuring out the world through their collisions with it.

Our debts run to both Galileo and to the authorities who muzzled him. It is not enough to celebrate the first. We must also learn to guard against the second.

Keeping the public informed is our duty, and not just because so much scientific research is taxpayer-funded. A public that is deeply informed, engaged, and enthusiastic about scientific advances is a public that directs not just its financial support but the interest and efforts of its children, its brightest minds, toward the most confounding challenges.

Even as we contemplate seeking out life in interstellar space, we must admit that we’ve not exhausted the possibilities within our own solar system; astro-archaeologists should also seek evidence of extraterrestrial life in our planetary backyard.