"Extraordinary claims require extraordinary evidence" is an adage attributed to astronomer Carl Sagan, but it could have been said by any decent scientist since the scientific method became accepted in the 17th century.
Sagan was referring to the search for extraterrestrial intelligence. Given the social, scientific, and cultural impact of confirming the existence of E.T., reasonable certainty is a minimum requirement to answer Enrico Fermi's famous question: "So where are they?"
The Fermi paradox posits that if life existed elsewhere in the universe in any great numbers, why is there no observable evidence of it? Mathematically, the chances of life arising on some other planet are as close to 100% as possible. But without evidence that proves life exists somewhere else, we're left with mathematical certainties but no physical facts.
A tantalizing clue may have been uncovered by a team of astronomers studying extrasolar planets using the most powerful telescope ever built: the James Webb Space Telescope (JWST).
Nikku Madhusudhan, an astronomer at the University of Cambridge and one of the authors of a new study published Wednesday in The Astrophysical Journal Letters.
Astronomers think they've found a "biosignature" emanating from a planet with the extremely boring name K2-18b, located about 120 light-years away. It's a kind of planet with which scientists are very familiar. They call this class of planets "sub-Neptunes" because of their enormous size, although they are smaller than Neptune in our solar system.
In 2021, Dr. Madhusudhan proposed a novel theory: "Sub-Neptunes were covered with warm oceans of water and wrapped in atmospheres containing hydrogen, methane, and other carbon compounds," according to the New York Times. He called these oceans "Hycean," a portmanteau of the words “hydrogen” and “ocean.”
The oceans would explain a lot of the observed molecular and other scientific markers that Madhusudhan and his team had discovered using ground-based telescopes.
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In 2021, the JWST came online. Madhusudhan's team was able to take a closer look at K2-18b, and what they found shocked them. They discovered a "biosignature" that could have only come from the presence of life. The molecule dimethyl sulfide is composed of sulfur, carbon, and hydrogen, and on Earth, it is only present where there are living organisms.
The reading was faint, and there was a chance it was false. So when they got the opportunity to study K2-18b again, they knew what to look for.
Last year, Dr. Madhusudhan and his colleagues got a second chance to look for dimethyl sulfide. As K2-18b orbited in front of its star, they used a different instrument on the Webb telescope to analyze the starlight passing through the planet’s atmosphere. This time they saw an even stronger signal of dimethyl sulfide, along with a similar molecule called dimethyl disulfide.
“It is a shock to the system,” Dr. Madhusudhan said. “We spent an enormous amount of time just trying to get rid of the signal.”
No matter how the scientists revisited their readings, the signal stayed strong. They concluded that K2-18b may in fact harbor a tremendous supply of dimethyl sulfide in its atmosphere, thousands of times higher than the level found on Earth. This would suggest that its Hycean seas are brimming with life.
It's at about this point that the rug is pulled out from under scientists claiming to have discovered life. Recall the infamous Mars rock ALH 84001 found in Antarctica in 1984 that Bill Clinton claimed was probably the real deal in a Rose Garden news briefing immortalized in the film "Contact." The rock was suggestive of life, but later studies confirmed the processes were naturally occurring.
“It’s important to remember that we’re just starting to understand the nature of these exotic worlds,” said Matthew Nixon, a planetary scientist at the University of Maryland.
Indeed, we've seen "Hot Jupiters, giant planets that orbit very close to their sun, "super Earths," "Rogue Planets" that have been ejected from their solar system, and "Ice Giants." The universe continues to surprise us with regard to its diversity and weirdness.
This could be a discovery of the ages. Or, it may be an interesting asterisk when we're finally able to confirm life exists outside of Earth. As with all things, the journey is as important as the destination. What we learn on the way to finding ET will change us as a species.
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