Before my morning jog at sunrise, I wrote a short new paper that opens a novel window to constraining the nature of dark matter based on data from gravitational-wave observatories. But my sense of intellectual relief was short lived, as I received a set of 10 questions about the search for extraterrestrial life. The email request came from a staff writer for the largest and most popular South Korean newspaper, with 1.5 million national readers and up to 20 million international readers in its daily circulation. Below are the answers I gave to each of the questions:
1. How likely do you think it is that extraterrestrial life exists — either within our Solar System or in other star systems? While the possibility of intelligent life remains, I imagine microbial life is more probable.
Indeed, microbial life is likely to exist in any place where warm liquid water with proper nutrients is present. This could hold in water oceans under the icy surface of moons or comets. In that case, microbes are far more prevalent than Earth-mass planets in the habitable zone of stars. Complex life, leading to animals with intelligence that eventually develop artificial intelligence (AI), should be rarer than microwave because it requires more conditions, involving — for example — an atmosphere and land-ocean interfaces where complex organisms thrive.
However, technological signatures might be far easier to detect than the molecular fingerprints of microbes in exo-planet atmospheres. Examples which I discussed in papers over the past decade include industrial pollution of exoplanet atmospheres, city-light on the surfaces of exoplanets, or interstellar technological artifacts near Earth — involving either functioning devices or space trash.
In a recent interview, I was asked whether I believe that the Solar system was visited by an alien artifact throughout its 4.6-billion-year history. I said that I believe so based on the existence of billions of Earth-Sun analogs and the fact that we already launched 5 probes out of the Solar system over the past half century. The interviewer was surprised to hear that my current scientific research within the Galileo Project is motivated by a belief. I explained that what defines scientists is not the belief that motivates their research, but their adherence to the scientific method that tests their hypothesis experimentally. New scientific knowledge is based on evidence, and in order to make discoveries we must be motivated by uncertain beliefs. The interviewer continued to ask: “But what if the motivating belief is wrong?” to which I replied: “It is a win-win situation, because we learn something new in the process.”
2. Given the vastness of the universe, isn’t it physically impossible for us to ever make contact with an alien civilization using current spacecraft technology?
This is a misconception. It will take the Voyager spacecraft about a billion years to reach the opposite side of the Milky-Way disk relative to the Sun. Most stars in the Milky-Way disk formed billions of years before the Sun. Any Galactic engineers like ours whose technological clock started billions of years before ours — because their star was born before the Sun, had enough time to reach us by now. Planaria are terrestrial animals that regrow organs when they get damaged or cut out of their bodies, and so they can live forever if fed. Extraterrestrial planaria would constitute ideal alien astronauts that can reach us alive over a travel period of billions of years, as long as the spacecraft protects them and provides the nutrients they need.
As soon as we can replicate the repair system of planaria for intelligent beings, we might send our own immortal passengers to interstellar space.
3. Would discovering extraterrestrial life — especially intelligent life — actually benefit us? Or could it potentially pose a threat to humanity?
The discovery of extraterrestrial intelligence will change the future of humanity for the better. If we discover extraterrestrial knowledge in science or technologies that we do not possess, it could trigger a quantum leap in our capabilities. This could have a major impact on our exploration of space, as well as on our commercial and military sectors. But most importantly, the discovery of technological miracles might inspire a sense of religious awe similar to the one felt by the biblical Moses when he witnessed the burning bush that was never consumed. Recognizing that there are siblings in our family of intelligent civilizations will empower rather than diminish the notion of God, because God must be able to care for multiple civilizations. The encounter with intelligent entities would allow us to resolve puzzles, such as: What happened before the Big Bang? What is dark matter and dark energy? What is inside a black hole? And what lessons can we learn from the history of intelligent civilizations that existed in the distant past or are still around in our cosmic neighborhood?
4. What kinds of findings do you anticipate from missions exploring Europa, Enceladus, Mars, or Titan?
My expectation is that future missions will find evidence for primitive life in the ocean under the surface ice of Europa and Enceladus as well as evidence that more complex lifeforms existed on Mars before it lost its atmosphere and became a desert in the second half of its history. I am particularly curious to know if intelligent life emerged on Mars twice as fast as it did on Earth. In that case, we might find wall paintings in the underground caves on Mars, which can be explored by Ingenuity-like helicopters with a video feed.
5. Could we detect extraterrestrial life through radio signals from space? Public interest has grown lately with the adaptation of science fiction works like The Three-Body Problem.
Radio signals are relatively easy to transmit and detect. The signals we produced with our most powerful anti-ballistic-missile radars for defense after World War II, can be detected by our current radio telescopes out to distances of a hundred light years. This means that a technological civilization like ours could detect us from that distance. However, only about a millionth of the Milky-Way stars reside within that distance, so it is unlikely that we will hear back a response any time soon. Even if they exist so close and decide to visit us, it will take a spacecraft like Voyager about a million years to reach us from that distance. For the time being, their silence is understandable.
6. With AI now capable of processing massive amounts of information, what role could it play in helping us detect or even communicate with alien civilizations?
Our AI is particularly effective in analyzing large data sets. This could be handy if we detect radio signals that need to be decoded, but it can also be used to identify rare objects of extraterrestrial technological origin among the many natural rocks we find near Earth. Within the Galileo Project, we are using AI to search for outliers among the millions of objects we detect in the sky from our observatory at Harvard University.
7. I understand that you’ve published research on ʻOumuamua, a unique interstellar object that passed through our Solar System. Has the possibility that it could be a kind of an interstellar spacecraft now been ruled out?
Unfortunately, astronomers obtained limited data on the anomalies of `Oumuamua that does not reveal its true nature. It was recognized as an interstellar object based on its high-speed relative to the Sun. But it also appeared to have an extreme shape, most likely flat and about a hundred meters in size, based on its reflection of sunlight. In addition, it was pushed away from the Sun by a mysterious non-gravitational force, without showing any evidence for cometary evaporation. This led me to suggest that its non-gravitational acceleration results from its high surface area per unit mass. A similar behavior was detected for another object 2020-SO, which was identified as a rocket booster from a 1966 launch by NASA. We know that 2020-SO was technological in origin because NASA produced it. The question is who produced `Oumuamua?
Starting in a couple of months, the Rubin Observatory in Chile could discover more family members of `Oumuamua every few months. I look forward to having much more data about them, also thanks to the Webb telescope that was not available when `Oumuamua was discovered. As a scientist, I love having a flood of data because it will not allow my colleagues to shove anomalies under the carpet. It is surprising for me to witness some scientists with anti-science sentiments. They wish to hold on to cherished beliefs even in the face of anomalies that contradict them. This is not surprising given that the Vatican admitted only in 1992 that Galileo was right, 350 years after he died and two decades after humans reached the Moon.
8. Astronomers have observed exoplanets located at optimal distances from their stars that may offer Earth-like conditions in terms of temperature and atmosphere. Do you believe these Earth “twins” might harbor life?
Any exoplanets that have an atmosphere and warm liquid water on their surface are likely to have life-as-we-know-it. The reason is simple. The Last Universal Common Ancestor (LUCA) for terrestrial life was DNA-dated recently to have emerged 4.2 billion years ago, only a few hundred million years after the formation of Earth and very soon after Earth cooled to temperatures that are suitable for the chemistry of life in liquid water. The emergence of life was rapid, implying that there are no major obstacles for life if the necessary conditions of warm liquid water and nutrients are met.
9. Is it possible that extraterrestrial life could follow biological mechanisms similar to ours — or might they exist based on entirely different scientific principles?
It is possible that there are other paths for life-as-we-do-not-know-it. For example, Titan is a moon of Saturn with liquid oceans, rivers and lakes of methane and ethane on its surface. I would love to go fishing there and check whether Titan gave rise to a completely different biological chemistry than the one we find in liquid water on Earth.
10. The search for extraterrestrial life is often associated with science fiction, the paranormal, or fringe theories. What, in your view, clearly distinguishes astrobiology and the scientific search for alien life as a legitimate scientific endeavor?
We know that we exist on Earth and we know that similar environments emerged around billions of stars in the Milky Way galaxy long before we came to exist. It is arrogant to think that we are unique. It is a matter of common sense to assume that we have intelligent siblings on exoplanets and in space. It is the obligation of astronomers to find them.
In an interview a few days ago, I was asked whether I search for aliens just to get the Nobel Prize. I replied: “Not at all. I hereby promise that if I discover extraterrestrial intelligence, I will decline the invitation by the Nobel committee to visit Stockholm, just like Bob Dylan or Jean-Paul Sartre did. Who would waste time on an old, traditional prize given by humans to humans on our planet if there is an opportunity to learn something really new from a superhuman intelligence from another star?”
ABOUT THE AUTHOR
Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.
