by Avi Loeb
Consider that cookbooks are full of recipes that have the same ingredients but result in different cakes, depending on the timing and fashion in which these ingredients are mixed and heated. Some cakes taste better than others. There is no reason to expect that terrestrial life, which emerged under random circumstances on Earth, was optimal. There may be other paths leading to better cakes.
The prospect of humanity producing synthetic life in the laboratory also raises interesting questions about our own origins. Are we the result of exclusively terrestrial evolution? Or did we, like the protocells being developed in university laboratories, receive a helping nudge?
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In 1871, in an address before the British Association for the Advancement of Science, the prolific physicist and mathematician Lord Kelvin suggested that life could have come to Earth by way of traveling meteorites.
The idea wasn’t original to Lord Kelvin. Ancient Greeks entertained the idea, and decades before Lord Kelvin’s address, other European scientists had given the possibility scrutiny. But despite the interest in the nineteenth century, following Kelvin’s presentation to the association in 1871 the idea went ignored for another century.
Over the past two decades, however, the theory of panspermia—the idea that life might reach habitable planets by way of meteorites, comets, or stardust—has been gaining more rigorous attention as scientific research confirmed the hypothesis that certain meteorites discovered on Earth were of Martian origin.
Once we began to seek these Martian meteorites, we found many more of them. We learned that ALH84001, a Martian meteorite that was found in Antarctica in 1984, had never been heated above 40 degrees Celsius (104 degrees Fahrenheit) after being ejected from the surface of Mars. To date, over a hundred such Martian landers have been identified. If there was ever life on the Red Planet, clearly it has had opportunities to reach Earth and survive.
Adding to the intrigue is the fact that scientific consensus has it that Earth was uninhabitable until about four billion years ago, and yet we have found evidence of life dating back 3.8 billion years. How is it possible, scientists asked, for Darwinian evolution to have so quickly produced DNA-based life? We know from terrestrial biology that life is self-serving. Selective and spontaneous adaptations that increase life’s ability to persevere is the bedrock of Darwinian biology. Life’s aim is survival, which means propagation. How plausible is it that life would make use of panspermia to spread and secure its survival?
In 2018, my postdocs Idan Ginsburg and Manasvi Lingam and I published a paper entitled “Galactic Panspermia” in which we presented an analytical model to estimate the total number of rocky or icy objects that could be captured by planetary systems within the Milky Way galaxy and result in panspermia should they harbor life.
We first considered whether we might be Martians. For life on Earth to be descended from life on Mars, the Red Planet would have to have been hit by an asteroid or comet with sufficient force that material was ejected into interplanetary space, and that material would have had to find its way to Earth. And, crucially, any life aboard would have had to survive the interplanetary voyage as well as the ejection and landing.
Mars has indeed been struck trillions of times by space debris larger than a person over the billions of years of its existence. Many impacts have resulted in temperatures and shock pressures guaranteed to kill any building blocks of life still clinging to the ejected rocks. But, as with the Martian meteorite ALH84001, some ejected materials did not exceed the boiling temperature of water, allowing some microorganisms to survive. This means that were there Martian life, it would still be living on rocks tossed into space by these gentler impacts. Scientists estimate that Mars has ejected billions of such fragments—objects with low enough temperatures to allow life to survive.
But even if the microorganisms survive their ejection from Mars, how plausible is it that they could survive the trip? There has been lively debate on this point, especially over how lethal ultraviolet radiation is to bacteria. But radioresistant bacteria with extreme tolerance to ultraviolet radiation and ionization have been discovered, and these strains could survive such a trip. (In fact, some terrestrial bacteria exhibit such extreme tolerances to UV and radiation that it is likely they originated on Mars.) What’s more, the hypothetical pool of surviving bacteria increases if we posit their traveling within a meteorite or comet in a way that shields them from UV radiation; such a rocky shielding could be as thin as just a few centimeters. And other studies have proven that spores of the bacteria Bacillus subtilis can survive in space for up to six years; other bacteria could live for vastly longer stretches of time, measurable in millions of years. Further, scientists have hypothesized a colony of bacteria that’s able to surround itself with a biofilm that greatly increases the organisms’ protection from harmful radiation.
In another paper, my undergraduate student Amir Siraj and I calculated that bacteria floating in the Earth’s atmosphere could have been scooped up by grazing objects that passed just fifty kilometers above sea level and then escaped the solar system. Such an interstellar-space-bound object would resemble a spoon passing through the foam on top of a cappuccino, only in this instance it would continue on with a residue of terrestrial life. We found that billions of such “spoons” have stirred the Earth’s atmosphere over the planet’s lifetime.
Would the bacteria have survived the trip? It is well known that fighter pilots can barely survive maneuvers with accelerations exceeding ten gs, where g is the gravitational acceleration that binds us to Earth. But Earth-grazing objects would scoop up microbes at accelerations of millions of gs. Could they live through the jolt? Possibly. Microbes such as Bacillus subtilis, Caenorhabditis elegans, Deinococcus radiodurans, Escherichia coli, and Paracoccus denitrificans have been shown to live through accelerations just one order of magnitude smaller. As it turns out, these mini-astronauts are far better suited for taking a space ride than our very best human pilots. They could survive the impact on Earth’s surface as long as their deep interiors were not overheated, similar to the Martian rock ALH84001.
This data tells us we cannot dismiss the possibility that we are of Martian origin. But might we be even more exotic? Might the truly original source of life on Earth, whether or not by way of a Martian layover, be interstellar or intergalactic? Yes. After conducting a rigorous analysis of the viability of panspermia, my colleagues and I determined that there is a parameter space that allows the galaxy to be saturated with life-bearing objects. While objects with lower velocities are more likely to be captured by the gravitational pull of a planet, and given the established fact that some bacteria can survive millions of years, we estimated that the probability of a life-bearing object striking a planet was significant. Indeed, by positing gravitational scattering events at the galactic center of the Milky Way, we projected that rocky material could be ejected at such extreme velocities that the center could have seeded the entire galaxy.
Those seeds need not even be restricted to bacteria. Certain viruses, which are also capable of Darwinian evolution, have proven themselves sufficiently durable. Even more complicated life might make the trip. Indeed, two roundworms discovered in the Arctic permafrost were revived after being in cryobiosis—when metabolic processes stop—for an estimated thirty to forty thousand years. If organisms such as these could survive the kinds of conditions and timescales that they might encounter on an interplanetary voyage, who’s to say they themselves aren’t descended from Martians?
Here is where the right bet on ‘Oumuamua’s wager could pay immediate dividends. Gamble that we have already seen evidence of extraterrestrial intelligence, and both the questions we ask and the projects we undertake shift. Consider that every scientific contortion we’ve just taken to arrive at the higher probability of naturally occurring panspermia is simplified if we entertain directed panspermia. How to ensure life is safely ejected from a planet? Eject it yourself. How to ensure life is sufficiently protected from the
harms of space while traveling between planets or galaxies? Build a rocket to the purpose. How to make sure life is nurtured and preserved to survive the extremely long journeys among galaxies? Build your rocket to that purpose too.
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Much depends on how we respond to ‘Oumuamua’s wager. The safest bet is to deem the object a peculiar rock, nothing more, and stick to our familiar habits of thought. But when so much is at stake, safe bets can only get us so far.
If we dare to wager that ‘Oumuamua was a piece of advanced extraterrestrial technology, we stand only to gain. Whether it prompts us to methodically search the universe for signs of life or to undertake more ambitious technological projects, placing an optimistic bet could have a transformative effect on our civilization. If humanity is able to think, plan, and build in pursuit of a vision measurable in millions of years, we just might manage to ensure that life in the universe is able to ride out the vast challenges of time and space by riding the flash of light from an exploding star. When I think of this familiar technology in that way, a lightsail tumbling in sunlight resembles nothing so much as the wings of a dandelion seed sent off by the wind to fertilize virgin soil.
Which brings us back to life originating in laboratories. Take the more cautious approach to ‘Oumuamua’s wager and we celebrate this extraordinary accomplishment solely for its implications for biomedical research. Take the more ambitious approach to ‘Oumuamua’s wager, and creating synthetic life in the laboratory becomes, potentially, a means for terrestrial life to outrun the great filter, even after the inevitable death of the Sun.
There is no doubt that if our civilization is bold enough and lasts long enough, we will eventually migrate into space—and into new regions of the universe that, in essential ways, resemble our current one. In doing so, we will surely be following in the footsteps of those who came before us; just as ancient civilizations migrated toward banks of rivers on Earth, advanced technological civilizations likely migrate throughout the universe toward environments that are rich in resources, from habitable planets to clusters of galaxies.
But no civilizations, very much including our own, will make the leap to migrating out among the stars if they are not smart enough to preserve their home planets while they plan and prepare. And it is an achievement humanity is less likely to attain when so many of us cling to the uniqueness of terrestrial life like that ant clung to that grain of sand.
13
Singularities
‘Oumuamua is extraterrestrial technological equipment.
That is a hypothesis, not a statement of fact. Like all scientific hypotheses, it awaits its confrontation with data. And as often happens in science, the data we have is not conclusive, but it is substantial.
Is there any chance that we could obtain additional data about ‘Oumuamua or similar objects beyond what we have already gleaned?
The last time we saw ‘Oumuamua, it was moving away from us incredibly quickly—many times faster than our fastest rocket. But of course, we could develop spacefaring technologies that are faster than rockets, like lightsails. Or we could approach the next ‘Oumuamua-like object with conventional rockets as it’s on its way toward us.
If we were to launch a spacecraft close to such an object, we might be able to photograph its surface. What evidence might we find? Almost all of it would be refinements on what we currently know. The right sorts of imaging would yield more data as to its size, its shape, its composition, its luminosity, perhaps even tell us if it bears obvious markers of its manufacturers, just as NASA always stamps its rockets with the American flag. Whatever the evidence is, I would welcome it.
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Unless and until we obtain additional evidence about ‘Oumuamua-like objects, we need to work with what we have. And what we have can be summed up with one repeating theme:
And yet it deviated.
‘Oumuamua, a small interstellar object first discovered by humans on October 19, 2017, that was highly luminous, oddly tumbling, and most likely disk-shaped, deviated from a path explicable by the Sun’s gravity alone without any visible outgassing. All of its properties, very much including its origin in space-time being local standard of rest, rendered it a statistical outlier to a highly significant degree. As a member of a population of objects on random orbits, it required much more solid material to be expelled than available in planetary systems around other stars. But if ‘Oumuamua was extremely thin or its orbit was not random, the problem could be alleviated.
Overwhelmingly, the scientific community has coalesced around the conclusion that ‘Oumuamua was a naturally occurring object, a peculiar, even exotic comet, but still, for all its peculiarities, just an interstellar rock. And yet it deviated.
It is true that we can hypothesize natural phenomena that could explain each of ‘Oumuamua’s observed exotic features. There is a statistical possibility, roughly one in one trillion, give or take, that ‘Oumuamua was a unique rock. But then ejecting enough material from planetary systems around nearby stars to supply a random population of ‘Oumuamua-like objects becomes even more challenging, because now one needs much more material in the form of normal interstellar objects, like 2I/Borisov.
Alternatively, the data allows another hypothesis: that ‘Oumuamua was extraterrestrial technology, perhaps defunct or discarded. In that data is something underappreciated by nearly everyone who has written on the subject. It is the fact that humanity could build within a mere few years a spacecraft that would demonstrate every single one of ‘Oumuamua’s features. In other words, the simplest, most direct line from an object with all of ‘Oumuamua’s observed qualities to an explanation for them is that it was manufactured.
The reason most of the scientific community cannot keep comfortable company with this hypothesis is that we didn’t manufacture it. To allow the possibility that another civilization did is to allow the possibility that one of the most profound discoveries—that we are not the only intelligence in the universe—has just passed through our solar system. It forces us into a new way of thinking.
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Accepting my hypothesis about ‘Oumuamua requires, above all else, humility, because it requires us to accept that while we may be extraordinary, in all likelihood we are not unique.
When I say we are extraordinary, I don’t mean it literally. That we are the stuff of stars is a poetic truism, but less poetically, it can also be said that the stars are made of the same stuff as us. That goes for the universe as well, for all that is within it started in the same dense soup of matter and radiation emanating from the Big Bang. Still, as I tell the students in my freshman seminar, although all of us are composed of the same ordinary matter, that does not preclude us from becoming extraordinary people. Far more significant is that the organization of the stuff we are made of has, over the course of millennia, become the stuff of life. And unlike everything we have discovered in the universe to date, we and we alone are so organized.
Extraordinary and unique are importantly different things. Consider Nicolaus Copernicus, the sixteenth-century astronomer who first proposed that the planets orbit the Sun and, in so doing, made a supposedly unique contribution to our conception of the cosmos. His book asserting this thesis was published shortly before his death in 1543, and it went largely ignored by all but a small number of astronomers, most of whom were Nicolaus’s friends. But today we trace the origins of a heliocentric solar system to Copernicus, and we use his name to describe the principle that neither Earth nor humanity occupies a special part of the universe, and, indeed, that the universe has no unique or special places. It is the same here, where humanity exists, as it is everywhere else. Today, we can add an ironic codicil to the Copernican principle: there is nothing special about a species and a civilization that has figured out this fundamental fact about the cosmos, for the same thing has likely been figured out by all civilizations everywhere else in the universe.
If we don’t merely entertain this thought but embrace it, we find ourselves
confronting amazing possibilities.
When Matias Zaldarriaga and I realized that human civilization produced a great deal of noise at the meter-wave radio spectrum, we thought it reasonable that another civilization might produce noise in the same radio band, and so we proposed seeking evidence of that. When Ed Turner and I realized that Tokyo would be visible through a Hubble Space Telescope placed out at the edge of our solar system, we thought it reasonable to seek a similar glimmer from another civilization’s city or spacecraft. Similarly, when my postdoc James Guillochon and I realized that humankind could feasibly send out lightsail-propelled spacecraft, we knew that it also stood to reason that another civilization could come to the same realization—and so we recommended a search for the telltale beams of radiation from such launches.
In that same spirit, it is reasonable to imagine that any such effort by another civilization to send a lightsail craft would have been preceded by something roughly equivalent to the launch of the Starshot Initiative—the project that we undertook to engineer (if not yet actually build) lightsails of our own.
I like to imagine I now know what they went through to get there.
I imagine the pacifists among them would have worried that a spaceship powered by a 100-gigawatt laser hurtling toward an alien civilization at a fraction of the speed of light could well be interpreted by them as threatening or even as a declaration of war. To which the chair of the advisory board of their version of the Starshot Initiative would likely have answered, as I did, that such a risk was infinitesimal. For starters, I said, we have no knowledge of the existence, let alone the nature, of extraterrestrial life, intelligent or not. If other beings do exist, our craft of only a few grams is unlikely to be noticed, and carrying the energy of a common asteroid, it would easily be classified as such. And it is an utter impracticality to try to aim our small craft to hit a planet light-years away. This would require an angular precision of a billionth of a radian and there is no way for us to know the relative positions of the planet and the spacecraft to that precision over the decades-long journey. No, rather than target a planet, the craft would aspire to approach an orbital region thousands of times larger than the size of a planet, implying a chance impact probability of less than one part in a million.