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Books
January 25, 2021 Issue


HAVE WE ALREADY BEEN VISITED BY ALIENS?

An eminent astrophysicist argues that signs of intelligent extraterrestrial life
have appeared in our skies. What’s the evidence for his extraordinary claim?

By Elizabeth Kolbert

January 18, 2021
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Encountering aliens would be surprising; the fact that we haven’t yet heard from
any is perhaps even more so.Illustration by Paul Sahre
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CONTENT

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On October 19, 2017, a Canadian astronomer named Robert Weryk was reviewing
images captured by a telescope known as Pan-STARRS1 when he noticed something
strange. The telescope is situated atop Haleakalā, a ten-thousand-foot volcanic
peak on the island of Maui, and it scans the sky each night, recording the
results with the world’s highest-definition camera. It’s designed to hunt for
“near-Earth objects,” which are mostly asteroids whose paths bring them into our
planet’s astronomical neighborhood and which travel at an average velocity of
some forty thousand miles an hour. The dot of light that caught Weryk’s
attention was moving more than four times that speed, at almost two hundred
thousand miles per hour.

Weryk alerted colleagues, who began tracking the dot from other observatories.
The more they looked, the more puzzling its behavior seemed. The object was
small, with an area roughly that of a city block. As it tumbled through space,
its brightness varied so much—by a factor of ten—that it had to have a very odd
shape. Either it was long and skinny, like a cosmic cigar, or flat and round,
like a celestial pizza. Instead of swinging around the sun on an elliptical
path, it was zipping away more or less in a straight line. The bright dot,
astronomers concluded, was something never before seen. It was an “interstellar
object”—a visitor from far beyond the solar system that was just passing
through. In the dry nomenclature of the International Astronomical Union, it
became known as 1I/2017 U1. More evocatively, it was dubbed ‘Oumuamua
(pronounced “oh-mooah-mooah”), from the Hawaiian, meaning, roughly, “scout.”



Even interstellar objects have to obey the law of gravity, but ‘Oumuamua raced
along as if propelled by an extra force. Comets get an added kick thanks to the
gases they throw off, which form their signature tails. ‘Oumuamua, though,
didn’t have a tail. Nor did the telescopes trained on it find evidence of any of
the by-products normally associated with outgassing, like water vapor or dust.

“This is definitely an unusual object,” a video produced by NASA observed. “And,
unfortunately, no more new observations of ‘Oumuamua are possible because it’s
already too dim and far away.”

As astronomers pored over the data, they excluded one theory after another.
‘Oumuamua’s weird motion couldn’t be accounted for by a collision with another
object, or by interactions with the solar wind, or by a phenomenon that’s known,
after a nineteenth-century Polish engineer, as the Yarkovsky effect. One group
of researchers decided that the best explanation was that 1I/2017 U1 was a
“miniature comet” whose tail had gone undetected because of its “unusual
chemical composition.” Another group argued that ‘Oumuamua was composed mostly
of frozen hydrogen. This hypothesis—a variation on the mini-comet idea—had the
advantage of explaining the object’s peculiar shape. By the time it reached our
solar system, it had mostly melted away, like an ice cube on the sidewalk.

By far the most spectacular account of 1I/2017 U1 came from Avi Loeb, a Harvard
astrophysicist. ‘Oumuamua didn’t behave as an interstellar object would be
expected to, Loeb argued, because it wasn’t one. It was the handiwork of an
alien civilization.

In an equation-dense paper that appeared in The Astrophysical Journal Letters a
year after Weryk’s discovery, Loeb and a Harvard postdoc named Shmuel Bialy
proposed that ‘Oumuamua’s “non-gravitational acceleration” was most economically
explained by assuming that the object was manufactured. It might be the alien
equivalent of an abandoned car, “floating in interstellar space” as “debris.” Or
it might be “a fully operational probe” that had been dispatched to our solar
system to reconnoitre. The second possibility, Loeb and Bialy suggested, was the
more likely, since if the object was just a piece of alien junk, drifting
through the galaxy, the odds of our having come across it would be absurdly low.
“In contemplating the possibility of an artificial origin, we should keep in
mind what Sherlock Holmes said: ‘when you have excluded the impossible, whatever
remains, however improbable, must be the truth,’ ” Loeb wrote in a blog post for
Scientific American.



Not surprisingly, Loeb and Bialy’s theory received a lot of attention. The story
raced around the world almost at the speed of ‘Oumuamua. TV crews crowded into
Loeb’s office, at the Harvard-Smithsonian Center for Astrophysics, and showed up
at his house. Film companies vied to make a movie of his life. Also not
surprisingly, much of the attention was unflattering.

“No, ‘Oumuamua is not an alien spaceship, and the authors of the paper insult
honest scientific inquiry to even suggest it,” Paul M. Sutter, an astrophysicist
at Ohio State University, wrote.

“Can we talk about how annoying it is that Avi Loeb promotes speculative
theories about alien origins of ‘Oumuamua, forcing [the] rest of us to do the
scientific gruntwork of walking back these rumors?” Benjamin Weiner, an
astronomer at the University of Arizona, tweeted.

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Far from being deterred, Loeb doubled down. Together with Thiem Hoang, a
researcher at the Korea Astronomy and Space Science Institute, he blasted the
frozen-hydrogen theory. In another equation-packed paper, the pair argued that
it was fantastical to imagine solid hydrogen floating around outer space. And,
if a frozen chunk did manage to take shape, there was no way for a block the
size of ‘Oumuamua to survive an interstellar journey. “Assuming that H2 objects
could somehow form,” Hoang and Loeb wrote, “sublimation by collisional heating”
would vaporize them before they had the chance to, in a manner of speaking, take
off.

Loeb has now dispensed with the scientific notation and written
“Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” (Houghton
Mifflin Harcourt). In it, he recounts the oft-told story of how Galileo was
charged with heresy for asserting that Earth circled the sun. At his trial in
Rome, in 1633, Galileo recanted and then, legend has it, muttered, sotto voce,
“Eppur si muove” (“And yet it moves”). Loeb acknowledges that the quote is
probably apocryphal; still, he maintains, it’s relevant. The astronomical
establishment may wish to silence him, but it can’t explain why ‘Oumuamua
strayed from the expected path. “And yet it deviated,” he observes.

In “Extraterrestrial,” Loeb lays out his reasoning as follows. The only way to
make sense of ‘Oumuamua’s strange acceleration, without resorting to some sort
of undetectable outgassing, is to assume that the object was propelled by solar
radiation—essentially, photons bouncing off its surface. And the only way the
object could be propelled by solar radiation is if it were extremely thin—no
thicker than a millimetre—with a very low density and a comparatively large
surface area. Such an object would function as a sail—one powered by light,
rather than by wind. The natural world doesn’t produce sails; people do. Thus,
Loeb writes, “ ‘Oumuamua must have been designed, built, and launched by an
extraterrestrial intelligence.”

The first planet to be found circling a sunlike star was spotted in 1995 by a
pair of Swiss astronomers, Michel Mayor and Didier Queloz. Its host star, 51
Pegasi, was in the constellation Pegasus, and so the planet was formally dubbed
51 Pegasi b. By a different naming convention, it became known as Dimidium.

Dimidium was the ‘Oumuamua of its day—a fantastic discovery that made headlines
around the world. (For their work, Mayor and Queloz were eventually awarded a
Nobel Prize.) The planet turned out to be very large, with a mass about a
hundred and fifty times that of Earth. It was whipping around its star once
every four days, which meant that it had to be relatively close to it and was
probably very hot, with a surface temperature of as much as eighteen hundred
degrees. Astronomers hadn’t thought such a large body could be found so close to
its parent star and had to invent a whole new category to contain it; it became
known as a “hot Jupiter.”

Mayor and Queloz had detected Dimidium by measuring its gravitational tug on 51
Pegasi. In 2009, NASA launched the Kepler space telescope, which was designed to
search for exoplanets using a different method. When a planet passes in front of
its star, it reduces the star’s brightness very slightly. (During the last
transit of Venus, in 2012, viewers on Earth could watch a small black dot creep
across the sun.) Kepler measured variations in the brightness of more than a
hundred and fifty thousand stars in the vicinity of the constellations Cygnus
and Lyra. By 2015, it had revealed the existence of a thousand exoplanets. By
the time it stopped operating, in 2018, it had revealed sixteen hundred more.




NASA’s ultimate goal for the telescope was to work out a figure known as
eta-Earth, or η⊕. This is the average number of rocky, roughly Earth-size
planets that can be found orbiting an average sunlike star at a distance that
might, conceivably, render them habitable. After spending two years analyzing
the data from Kepler, researchers recently concluded that η⊕ has a value
somewhere between .37 and .6. Since there are at least four billion sunlike
stars in the Milky Way, this means that somewhere between 1.5 billion and 2.4
billion planets in our galaxy could, in theory, harbor life. No one knows what
fraction of potentially habitable planets are, in fact, inhabited, but, even if
the proportion is trivial, we’re still talking about millions—perhaps tens of
millions—of planets in the galaxy that might be teeming with living things. At a
public event a few years ago, Ellen Stofan, who at the time was NASA’s chief
scientist and is now the director of the National Air and Space Museum, said
that she believed “definitive evidence” of “life beyond earth” would be found
sometime in the next two decades.



“It’s definitely not an ‘if,’ it’s a ‘when,’ ” Jeffrey Newmark, a NASA
astrophysicist, said at the same gathering.

What will life on other planets look like, when—not if—it’s found? Arik
Kershenbaum, a researcher at the University of Cambridge, takes up this question
in “The Zoologist’s Guide to the Galaxy: What Animals on Earth Reveal About
Aliens—and Ourselves” (Penguin Press). “It’s a popular belief that alien life is
too alien to imagine,” he writes. “I don’t agree.”

Kershenbaum argues that the key to understanding cosmic zoology is natural
selection. This, he maintains, is the “inevitable mechanism” by which life
develops, and therefore it’s “not just restricted to the planet Earth” or even
to carbon-based organisms. However alien biochemistry functions, “natural
selection will be behind it.”

From this premise, Kershenbaum says, it follows that life on other planets will
have evolved, if not along the same lines as life on this planet, then at least
along lines that are generally recognizable. On Earth, for instance, where the
atmosphere is mostly made of nitrogen and oxygen, feathers are a useful feature.
On a planet where clouds are made of ammonia, feathers probably wouldn’t emerge,
“but we should not be surprised to find the same functions (i.e. flight) that we
observe here.” Similarly, Kershenbaum writes, alien organisms are apt to evolve
some form of land-based locomotion—“Life on alien planets is very likely to have
legs”—as well as some form of reproduction analogous to sex and some way of
exchanging information: “Aliens in the dark will click like bats and dolphins,
and aliens in the clear skies will flash their colours at each other.”

Assuming that there is, in fact, alien life out there, most of it seems likely
to be microscopic. “We are not talking about little green men” is how Stofan put
it when she said we were soon going to find it. “We are talking about little
microbes.” But Kershenbaum, who studies animal communication, jumps straight to
complex organisms, which propels him pretty quickly into Loebian territory.

On Earth, many animals possess what we would broadly refer to as “intelligence.”
Kershenbaum argues that, given the advantages that this quality confers, natural
selection all across the galaxy will favor its emergence, in which case there
should be loads of life-forms out there that are as smart as we are, and some
that are a whole lot smarter. This, in his view, opens up quite a can of
interstellar worms. Are we going to accord aliens “human rights”? Will they
accord us whatever rights, if any, they grant their little green (or silver or
blue) brethren? Such questions, Kershenbaum acknowledges, are difficult to
answer in advance, “without any evidence of what kind of legal system or system
of ethics the aliens themselves might have.”

As disconcerting as encountering intelligent aliens would be, the fact that we
haven’t yet heard from any is, arguably, even more so. Why this is the case is a
question that’s become known as the Fermi paradox.

One day in 1950, while lunching at Los Alamos National Laboratory, the physicist
Enrico Fermi turned to some colleagues and asked, “Where are they?” (At least,
this is how one version of the story goes; according to another version, he
asked, “But where is everybody?”) This was decades before Pan-STARRS1 and the
Kepler mission. Still, Fermi reckoned that Earth was a fairly typical planet
revolving around a fairly typical star. There ought, he reasoned, to be
civilizations out there far older and more advanced than our own, some of which
should have already mastered interstellar travel. Yet, strangely enough, no one
had shown up.

Much human intelligence has since been devoted to grappling with Fermi’s
question. In the nineteen-sixties, an astronomer named Frank Drake came up with
the eponymous Drake equation, which offers a way to estimate—or, if you prefer,
guesstimate—how many alien cultures exist with which we might hope to
communicate. Key terms in the equation include: how many potentially habitable
planets are out there, what fraction of life-hosting planets will develop
sophisticated technology, and how long technologically sophisticated
civilizations endure. As the list of potentially habitable planets has grown,
the “Where are they?” mystery has only deepened. At a workshop on the subject
held in Paris in 2019, a French researcher named Jean-Pierre Rospars proposed
that aliens haven’t reached out to us because they’re keeping Earth under a
“galactic quarantine.” They realize, he said, that “it would be culturally
disruptive for us to learn about them.”



Loeb proposes that Fermi may be the answer to his own paradox. Humanity has been
capable of communicating with other planets, via radio wave, for only the past
hundred years or so. Seventy-five years ago, Fermi and his colleagues on the
Manhattan Project invented the atomic bomb, and a few years after that Edward
Teller, one of Fermi’s companions at the lunch table at Los Alamos, came up with
the design for a hydrogen bomb. Thus, not long after humanity became capable of
signalling to other planets, it also became capable of wiping itself out. Since
the invention of nuclear weapons, we’ve continued to come up with new ways to do
ourselves in; these include unchecked climate change and manufactured microbes.




“It is quite conceivable that if we are not careful, our civilization’s next few
centuries will be its last,” Loeb warns. Alien civilizations “with the
technological prowess to explore the universe” are, he infers, similarly
“vulnerable to annihilation by self-inflicted wounds.” Perhaps the reason no one
has shown up is that there’s no one left to make the trip. This would mean that
‘Oumuamua was the cosmic equivalent of a potsherd—the product of a culture now
dead.

A message an earthling might take from this (admittedly highly speculative)
train of thought is: be wary of new technologies. Loeb, for his part, draws the
opposite conclusion. He thinks humanity ought to be working to produce precisely
the kind of photon-powered vessel that he imagines ‘Oumuamua to be. To this end,
he’s an adviser on a project called the Breakthrough Starshot Initiative, whose
stated aim is to “demonstrate proof of concept for ultra-fast light-driven
nanocrafts.” In the longer term, the group hopes to “lay the foundations” for a
launch to Alpha Centauri, the star system closest to Earth, which is about
twenty-five trillion miles away. (The initiative has funding from Yuri Milner, a
Russian-Israeli billionaire, and counts among its board members Mark
Zuckerberg.)

Loeb also looks forward to the day when we’ll be able to “produce synthetic life
in our laboratories.” From there, he imagines “Gutenberg DNA printers” that
could be “distributed to make copies of the human genome out of raw materials on
the surface of other planets.” By seeding the galaxy with our genetic material,
we could, he suggests, hedge our bets against annihilation. We could also run a
great evolutionary experiment, one that might lead to outcomes far more wondrous
than seen so far. “There is no reason to expect that terrestrial life, which
emerged under random circumstances on Earth, was optimal,” Loeb writes.

When I was a kid, one of my favorite books was “Chariots of the Gods?,” by Erich
von Däniken. The premise of the book, which was spun off into the TV documentary
“In Search of Ancient Astronauts,” narrated by Rod Serling, was that Fermi’s
question had long ago been answered. “They” had already been here. Von Däniken,
a Swiss hotel manager turned author who for some reason in the documentary was
described as a German professor, argued that aliens had landed on Earth sometime
in the misty past. Traces of their visits were recorded in legends and also in
artifacts like the Nazca Lines, in southern Peru. Why had people created these
oversized images if not to signal to beings in the air?

I figured that von Däniken would be interested in the first official
interstellar object, and so I got in touch with him. Now eighty-five, he lives
near Interlaken, not far from a theme park he designed, which was originally
called Mystery Park and then later, after a series of financial mishaps,
rebranded as Jungfrau Park. The park boasts seven pavilions, one shaped like a
pyramid, another like an Aztec temple.

Von Däniken told me that he had, indeed, been following the controversy over
‘Oumuamua. He tended to side with Loeb, who, he thought, was very brave.

“He needs courage and obviously he had courage,” he said. “No scientist wants to
be ridiculed, and whenever they deal with U.F.O.s or extraterrestrials, they are
ridiculed by the media.” But, he predicted, “the situation will change.”

It’s often said that “extraordinary claims require extraordinary evidence.” The
phrase was popularized by the astronomer Carl Sagan, who probably did as much as
any scientist has done to promote the search for extraterrestrial life. By
what’s sometimes referred to as the “Sagan standard,” Loeb’s claim clearly falls
short; the best evidence he marshals for his theory that ‘Oumuamua is an alien
craft is that the alternative theories are unconvincing. Loeb, though,
explicitly rejects the Sagan standard—“It is not obvious to me why extraordinary
claims require extraordinary evidence,” he observes—and flips its logic on its
head: “Extraordinary conservatism keeps us extraordinarily ignorant.” So long as
there’s a chance that 1I/2017 U1 is an alien probe, we’d be fools not to pursue
the idea. “If we acknowledge that ‘Oumuamua is plausibly of
extraterrestrial-technology origin,” he writes, “whole new vistas of exploration
for evidence and discovery open before us.”



In publishing his theory, Loeb has certainly risked (and suffered) ridicule. It
seems a good deal more likely that “Extraterrestrial” will be ranked with von
Däniken’s work than with Galileo’s. Still, as Serling notes toward the end of
“In Search of Ancient Astronauts,” it’s thrilling to imagine the possibilities:
“Look up into the sky some clear, starlit night and allow yourself the freedom
to wonder.” ♦





Published in the print edition of the January 25, 2021, issue, with the headline
“Swinging on a Star.”

Elizabeth Kolbert, a staff writer at The New Yorker since 1999, won the 2015
Pulitzer Prize for “The Sixth Extinction.” Her latest book is “Under a White
Sky: The Nature of the Future.”

More:AstronomySpaceAliensExtraterrestrialsAstrophysicistsBooksNational
Aeronautics and Space Administration


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