About the lead image: It is an artwork from 1974 titled ‘Li I’ by the Swiss painter HR Giger—best known for creating the fictional Xenomorph creatures from the iconic 1979 film ‘Alien’.

First, an entertaining history lesson

The first known speculation about ET—at least in the West—dates back to the ancient Greeks. As always, they were rather pompous about it:

Epicurus’ disciple Metrodorus of Chios considered the idea of our “world” being the only one as unlikely as “if a single ear of wheat grew on a vast plain.” As the Roman Epicurean poet Lucretius put it: “Nothing in the universe is unique and alone and therefore in other regions there must be other earths inhabited by different tribes of men and breeds of beasts.”

But by the time we hit the Middle Ages, no good Christian could bear the idea of God creating any species more worthy than Man. Those who conceded the possibility of aliens were distracted by weighty matters such as this:

As to the question whether Christ dying on this earth could redeem the inhabitants of another world, I would answer that he is able to do this even if the worlds were infinite. But it would not be fitting for him to go unto another world that he must die again. 

Christian aliens. It’s complicated! 

Cue, the modern astronomer: We didn’t start looking for aliens in earnest until the 1950s. Astrophysicist Frank Drake scanned the skies with radio telescopes hoping to catch a signal from distant galaxies. He also proposed the Drake Equation—the second-most famous after E= mc2—at a meeting of great minds in 1961 (which included the greatly beloved Carl Sagan). 

The equation claims to calculate the number of advanced alien worlds in the universe—but almost all of its nine variables are entirely unknown. Example: The number of planets in a solar system that have an environment suitable for life. Who knows! Btw, after all these decades, we can still only estimate one of Drake’s variables: The rate of production of stars. Nevertheless, back in 1961, the assembled scientists took a wild guess that “new transmitting societies appear once a year somewhere in the Milky Way.” Because why not 🤷🏽

OTOH, there’s Enrico Fermi: The Italian physicist pointed out the glaringly obvious: If the universe is teeming with intelligent life, where the eff are the aliens? 

Our Milky Way alone contains an estimated 100 to 400 billion stars, many of them hosting planets in the habitable zone. If even a tiny fraction of these planets develop life, and a fraction of those develop intelligence and technology, the galaxy should be buzzing with signals, megastructures, or even interstellar visitors. But so far, we’ve found nothing.

Another way to think about the sheer scale of this seeming nothingness: There are about 10,000 stars for every grain of sand on Earth.

Point to note: One answer to the Fermi Paradox is that it’s just a matter of bad timing: Humans haven’t been around that long—and we’ve been scanning the skies for less than a century. Hence, it is unlikely that we will overlap with any other intelligent life.  

Editor’s note: We did not look at similar speculation in ancient Indian treatises—primarily because it is now fully entwined in Hindutva mythmaking. 

Behold the ‘signature of life’! 

Late last week—just in time for an Easter miracle—a team of Cambridge researchers announced that they had found “the strongest indication yet of extraterrestrial life.” It is located on a planet called K2-18b—orbiting a star 120 light-years from Earth. The lead researcher—Nikku Madhusudhan—waxed rhapsodic about his own word—modestly described as “potentially one of the biggest landmarks in the history of science.” The reason: “It’s the first time humanity has seen potential biosignatures on a habitable planet.” 

Wtf is a ‘biosignature’? No, it isn’t a radio signal (sorry, Frank)—or even evidence of a lifeform. The potential “sign of life” in this case is dimethyl sulfide, which is made of sulfur, carbon, and hydrogen. On Earth, only living organisms produce this stuff: “In the ocean, for instance, certain forms of algae produce the compound, which wafts into the air and adds to the sea’s distinctive odor.”

Say hello to the ‘Hycean world’: Data from the James Webb Space Telescope suggest K2-18b has a vast ocean—and is surrounded by a hydrogen-rich atmosphere. Hydrogen + Ocean = Hycean. Yes, the term is also Madhusudhan’s doing—coined back in 2021. So what swims in these Hycean waters? One Cambridge collaborator suggests the presence of complex microbes: “It’s very, very speculative. But our models would be consistent with having complex phytoplankton.” 

The big Q: ‘Biosignature’ or bio-fertilizer? 

Some scientists think everything about the Cambridge data is “very, very speculative”—so much so that Madhusudhan’s MIT grad adviser dismissed it as “enthusiasm is outpacing evidence.” To explain why, let’s start with methodology.

Gathering the data: Contrary to what the headlines suggest, no one has seen our star rock K2-18b:

[W]e only know it’s there because its host star dims at regular intervals when the planet passes in front of it. Madhusudhan and his team used the James Webb Space Telescope to collect light from K2-18b’s host star during one of these transits by the planet. A tiny fraction of the light they collected shone directly through the planet’s atmosphere, and that light carried a record of the molecules that it encountered there all the way to the Webb.

One of these molecules is dimethyl sulfide—produced by marine algae on Earth and in Hycean seas. Or not. 

Big ‘but’ #1: Madhusudhan et al say K2-18b has a warm and welcoming ocean. But other scientists insist it is instead a great, nasty pit of molten magma.

Big ‘but’ #2: Just because dimethyl sulfide can only be produced by living organisms on Earth, it doesn’t mean that the rule holds true on other planets. Unfortunately for the revolutionary Mr Madhusudhan, it has also been detected on entirely uninhabited comets.

Biggest ‘but’ #3: It’s not certain if the researchers even detected the tell-tale molecule, according to Ross Andersen in The Atlantic: 

The details are too technical to get into here, but the important thing to know is that Madhusudhan and his team did not directly detect dimethyl sulfide. The chemical is only one of several that could be responsible for the signal they found. And although it’s the most likely one according to their models, others disagree.

Other ill omens to note: The deafening silence over at NASA, the European Space Agency, and the Canadian Space Agency. When asked what we know about K2-18b, the associate director of the institute that operates the JWS Telescope said: “We know there is a planet there; we know that.” Ouch!

So what do we make of this? 

Let’s set aside whether the Cambridge team got it right or not. The debate itself offers an intriguing look at the search for intelligent life—right now! What does it tell us?

One: Thanks to powerful new technology like JWST, scientists are confident that we will find evidence of alien life before the end of this decade. Even if Madhusudhan is wrong—he is maybe just jumping the gun. As one astrophysicist bluntly says: “The point is, after 2,500 years of people yelling at each other over life in the universe, in the next 10, 20 and 30 years we will actually get data.”

Two: The existence of aliens is not a yes/no proposition. It is highly likely that there is microbial life in the universe—just not the kind that Fermi was talking about:

Seti’s Andrew Siemion suggests there’s a 40% chance extraterrestrial life, when detected, will be intelligent. His reasoning: microbial life is widespread but uncommunicative. Intelligent life is the reverse.

Three: We don’t even know what an alien biosignature would look like:

Here on Earth, biology involves DNA and carbohydrates and requires liquid water, but the chemistry could be different on other worlds. Maybe life could use liquid methane instead of water, or silicon instead of carbon. So, in its most fundamental formulation, what is life all about, and how do we know what to look for?

Would we be able to identify alien life if we saw it? We have 100 definitions of life on Earth—imagine agreeing on any that holds true for the universe. 

Four: Evidence of intelligent life is very different from that of microbes. Since 2018, a group of 60 researchers are looking for ‘technosignatures’—ather than biosignatures. These scientists are looking for stuff in the atmosphere that cannot have a natural source. For example: air pollution from industrial byproducts like nitrogen trifluoride,. We will be able to look for these kinds of emissions with a NASA space telescope—known as LUVOIR (Large Ultraviolet Optical Infrared Surveyor)—to be deployed after 2040.

Point to note: As these scientists point out, technosignatures may be far more unlikely—but they will also be very hard to miss. Just look at the kind of space junk we’ve managed to generate in just decades. 

But, but, but: That view is itself skewed by human history—or even Western science:

Indigenous societies were at least thousands of years old — older than science itself. And yet [Hilding Neilson] wondered if they were considered “advanced” by Western definitions. In the case of looking for life elsewhere, he remarked, “we’re really looking for ourselves in space.”

See how we loop right back to us again?

So where does that leave us?

On the one hand: Embracing the alien-ness of alien life. We at least know what we don’t know—whether life is buried underground on Mars—or floating in icy seas on Jupiter’s moon Europa. It may be impossible to see these microbes on a telescope—or even a flyby. There are even wilder theories about why we can’t see aliens—including a 2024 paper on planet-less aliens hanging out in space:

[T]he researchers paint the picture of a.. free-floating colony of organisms measuring up to 330 feet (100 meters) across, encased in a thin, hard, transparent shell that could maintain a livable temperature and pressure through the greenhouse effect.

Imagine if one of them came sailing over the horizon! Well, at least it would be very hard to miss.

But, but, but: Once the space dust settles, our search for intelligent life may teach us most about the species we know and fear far too well—ourselves:

“If we find biosignatures, that means there’s a bunch of planets that can have life on them,” Haqq-Misra told me. But if we find plentiful signs of life but no signs of technology, that’s more worrisome. It could mean the odds are against technological civilizations sustaining themselves. They may be exceedingly rare — or tend to self-destruct.

 

“On the other hand,” Haqq-Misra added, “what if we find technosignatures everywhere? That’s actually encouraging. That means that it’s possible to have technology in a long-term, sustainable balance with your planet.”

And that may be the true lesson (and bottomline) of this very human quest. 

Reading list

USA Today has a good explainer on whether the planet K2-18b shows signs of life. Slate looks at the history of possible alien encounters, while Tortoise Media has more background on the search for alien life. OTOH Live Science gets into the 12 strange reasons humans haven't found alien life yet and The Atlantic debunks the research. The Conversation and The Guardian look at what the new findings mean and the new hope of finding alien life. BBC News has more on what it means for humans. Aeon has a good read on the possibility of alien life being closer to home.