Astronomers made headlines last week by suggesting potential signs of life on the distant exoplanet K2-18b—but is this truly our first glimpse of extraterrestrial beings, or simply wishful thinking?
Early James Webb Space Telescope readings hinted that K2‑18b harbors a hydrogen‑rich atmosphere containing carbon dioxide, methane and a possible trace of dimethyl sulfide—a gas on Earth generated almost exclusively by living organisms. Because the planet orbits within the temperate “Goldilocks” zone about 120 light‑years away, some astronomers argue that a deep global ocean beneath its clouds could be habitable. Others caution that these signatures sit at the edge of detectability, and non‑biological chemistry could easily mimic them.
To cut through the speculation, we consulted Stacy McGaugh, professor of astronomy at Case Western Reserve University, to discuss the controversial discovery, the realities of interstellar communication, and why, despite decades of searching, the universe remains eerily silent.
Read on to glean his insights into what this moment means for science—and why, in McGaugh’s view, the Fermi Paradox might not be a paradox at all.
Q: Some researchers have pointed to K2-18b as showing potential signs of life. How do you view the validity of that claim?
McGaugh: There has been a lot of pushback among exoplanet scientists as to whether this signal is indeed a biosignature as claimed. They make good points. It isn’t clear that there is a signal at all (the formal significance is low) and there are non-biological processes that might give that signal if it is real.
Q: The Fermi Paradox asks why, if intelligent alien life is likely, we haven’t seen any signs of it. What are your thoughts on this?
McGaugh: I don’t see it as a paradox at all. Space is big. I mean, really, really BIG, and mostly empty. Our galaxy contains hundreds of billions of stars, so I agree with Enrico Fermi’s optimism that other life is likely to be out there, but I am less sanguine that it would be able to communicate with us. The Earth has had life on it for billions of years, but for most of that time it was only single-celled organisms. We have broadcast radio signals that others might detect for less than two centuries, so our own broadcasts have not gotten very far across a galaxy that is 100,000 light-years in diameter. From that perspective, I’m not surprised that we don’t see signals from lots of other civilizations.
Q: The Drake Equation is often used to estimate how many intelligent civilizations might exist in our galaxy. How useful do you think it is in actually answering that question?
McGaugh: Frank Drake was also an optimist, and used this now-eponymous equation to justify launching the search for extraterrestrial intelligence (SETI, which is now big business). It attempts to estimate the number of intelligent civilizations there are in our galaxy currently that we might conceivably hear a radio signal from. I have students do this as an exercise; this is what they came up with last time. We know too little for this to be a meaningful exercise, but it does help with perspective.
Q: Even if intelligent life exists elsewhere, why might we still never encounter it?
McGaugh: As you can see from the above exercise, it is easy to come to the conclusion that there is less than one intelligent species like ourselves in the entire galaxy at any given time. We may come and go like popcorn…it depends a lot on how long our advanced civilizations endure. It needs to be a very long time indeed for there to be more than one at a time. Even then, we are few and very far apart. And even that scenario only works if each intelligent species manages to sustain its technologically advanced civilization for millennia—and continues to progress to the point of being able to travel between stars, not just reach the much lower threshold of emitting radio signals envisioned by Drake.