For more than 70 years, scientists have sought evidence of intelligent aliens by hunting for radio signals — interstellar messages beamed billions of miles across space. But for Harvard astrophysicist Avi Loeb, the search for extraterrestrial intelligence begins much closer to home: In Earth's oceans.
In summer 2023, Loeb led an expedition near Papua New Guinea to dredge up hundreds of tiny metal spheres he proposed were potential remnants of an interstellar meteor that broke up over the Pacific Ocean a decade earlier. For Loeb, this mission wasn't just about finding rare evidence of an object from beyond our solar system — but also a chance to probe the spheres for traces of potential alien technology.
The expedition's lofty goal garnered criticism from the scientific community — but for Loeb, even a faint possibility of learning something new about our cosmos is reason enough to investigate.
"I'm not pretending to know more than I know," Loeb told Live Science in an interview. "I'm willing to consider possibilities that others may completely discount."
Loeb, who is a professor of astrophysics and the Director of the Institute for Theory and Computation at the Harvard-Smithsonian Center of Astrophysics, says he came by his academic success unintentionally, after a lifelong passion for philosophy led him to astrophysics. Live Science caught up with the professor ahead of the HowTheLightGetsIn festival in London, where Loeb will be speaking later this month, to discuss his research, his hopes for future expeditions, and the search for extraterrestrial intelligence.
Brandon Specktor: You’ve said that, from a young age, you wanted to be a philosopher. Do you have a philosophy that guides your scientific research?
Avi Loeb: Humans, in general, existed for a few million years on Earth, which is just one part in 10,000 of the age of the universe. So we just came at the end of the cosmic play. And we know, thanks to Copernicus and Galileo, that we are not at the center of stage. And so the play is not about us. And we better stay humble and curious. That's my fundamental philosophy.
BS: You've shared many ideas about where humans should look for extraterrestrial life. If you were given a blank check to pursue any of your ideas about aliens, how would you spend it?
AL: I think we should do a better job with Mars, because Mars had liquid water on the surface. We know that for sure. There was some preliminary evidence that perhaps the soil on Mars has some tantalizing signatures of life that were first hinted at with the Viking mission [in 1976]. There are lots of things we can do which are not more difficult than were done already in the '70s. It's just a pity that NASA is not doing it.
[Editor’s note: NASA has collected as many as 30 geological samples on Mars, and is working with the private sector to develop a plan to return them to Earth for analysis. The budget for such missions remains an issue.]
Another thing I would do is, there are millions of objects, roughly a meter in size, that came from outside the solar system. At any point in time, there are a few millions of those that are within the orbit of the Earth around the sun. They don't reflect enough sunlight for us to discover them with our existing telescopes. So I would establish an experimental program attempting to detect them.
I would like to see if, among the rocks that arrive into the solar system from other stars, there is any technological debris. It could be space trash or it could be functional, but it should be easy to differentiate between rocks and something else. So if I had all the money in the world, I would establish an experimental program to monitor objects within the orbit of the Earth around the sun.
We have already detected 'Oumuamua, an interstellar object about 100 meters [330 feet] in size — the size of [SpaceX's] Starship, the biggest spacecraft that humans ever produced. There must be many more objects that are much smaller.
BS: Can future satellites — like NASA's NEO Surveyor, an infrared telescope focused on tracking near-Earth objects — help detect potentially interstellar objects?
AL: Definitely. But only if they come close to Earth. There will be a bigger telescope called the [Vera C.] Rubin Observatory in Chile that will start operations in 2025, and that will likely find many more interstellar objects close to Earth, or within Earth's orbit around the sun. I'm working with my postdocs and students on a program to find those as soon as the data comes in from the Rubin Observatory.
I'm very excited. You see, if you are driven by curiosity, additional data is a blessing. If you are driven by something else, like showing off or establishing your stature, then you would respond to something like Oumuamua the way one of my colleagues did — saying "I wish it never existed."
I would like to see if, among the rocks that arrive into the solar system from other stars, there is any technological debris. It could be space trash or it could be functional. "
Avi Loeb, Harvard astrophysicist
You see that quite routinely in science, where you have experts that are disturbed and really upset about anomalies. They claim the anomalies do not exist. There is nothing new. We already know everything. The people who are pointing out the anomalies should be discredited. The papers should be ignored ... We should forget about it, and move on. You see that, and unfortunately, that suppresses the progress of science.
BS: You've received some pushback on a recent study of metal spherules that you dredged from the ocean near Papua New Guinea, which you claim to be pieces of an interstellar meteor. Do you put any stock in papers that are critical of your findings? Do you read them with an open mind and see if they actually have compelling evidence?
AL: Yeah. So for example, there was a claim that what we recovered is coal ash. So we looked at 55 elements from the periodic table after this claim was made and showed that it's not coal ash. We made a diagram in which we demonstrated that the abundances of many chemical elements is not that of coal ash.
I submitted this research note to a journal that published the original argument that it's coal ash. The editor said, "well, I'm not sure that there is a point in publishing this"… So I wrote to the chief editor above him, and eventually it got published.
This is all to say that there is an agenda sometimes behind what is happening. It's not a fair game.
BS: So are you planning on returning to Papua New Guinea to look for more evidence of this meteor?
AL: We are planning to do it again in a year. I announced it a few months ago, and I have a few interested parties in funding it. It will be $6.5 million.
BS: How will this expedition be different from the last one?
AL: Last time, we were at sea just for two weeks. The equipment we designed collected the tiny spherules less than a millimeter in size, less than the size of a grain of sand. Of course, that was very valuable, allowing us to find that a fraction of them, 10% of them, had an unusual chemical composition. But it still doesn't tell us the nature of the object. Because these were molten droplets that lost some elements in the process of being molten.
What we want to find are bigger pieces, a centimeter in size, at least several millimeters, that we can use to, first of all, get a full census of all the chemical elements. But also we can examine the material properties. We know that this object had a material strength tougher than even iron meteorites from the solar system because it exploded only in the lower atmosphere where the stress was much greater than witnessed by other meteorites. We want to test the material properties. Also, if we get a big piece, we can do isotope analysis and date the age of the material to demonstrate that it's different from the age of the solar system.
Finally, most importantly, is that we can tell if it's a natural object like a rock or something else, a part of a gadget. The next expedition, we will use a remotely operated vehicle that we will place on the ocean floor, and we will have a video feed, and it will collect [spherule samples]. The hope is to collect bigger pieces and examine them in the laboratory afterwards.
There could be a lot of space trash generated by past civilizations. We have been searching for radio signals for 70 years. We need to change the approach."
Avi Loeb, harvard astrophysicist
BS: How confident are you that we will find evidence of alien life in your lifetime?
AL: I'm very hopeful because [we are taking] a path that was not taken before, in this case, searching for the nature of objects that arrived into the solar system from outside. The traditional [search for intelligent life] was for radio signals, which is just like waiting for a phone call. Here, we're looking for packages that may be in our mailbox. It's a very different approach. I'm hopeful that we will see something unusual, especially since two out of the known three interstellar objects appear to be weird, we will learn something new. I think within the coming years, there is a good chance that there would be exciting results, either from the Rubin Observatory or the expeditions that we are planning. After the one I mentioned to you, we will go for the second interstellar meteor that is between Portugal and the Azores. It's a very different place.
BS: And just to be clear, you think studying interstellar objects is the most promising avenue for finding evidence of alien life?
AL: I think so. First of all, it's easy to tell the difference between a natural object and an artificial object. There could be a lot of space trash generated by past civilizations. We have been searching for radio signals for 70 years. We need to change the approach. Frankly, radio communication was just a very early technology that humanity developed. However, space exploration, to me, sounds like a generic activity that an advanced civilization will engage in. We should search for those things. I think there is a chance we will find something remarkable. Obviously, without searching, we will not find anything.
It's just like Blaise Pascal argued that you can't just dismiss offhand the possibility that God exists, because if God does exist, the implications are huge. That was the argument of Pascal. I revised it in the context of extraterrestrials. I say, this has to be part of the mainstream of scientific inquiry, because the implications are huge.
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