Postcard from Interstellar Space: Separating the Wheat from the Chaff
There are hundreds of billions of stars in the Milky-Way galaxy and a substantial fraction of them host a habitable Earth-like planet. Most of them formed billions of years before the Sun, the time it will take Voyager to reach the other side of the Milky-Way disk, according to a recent paper I wrote with my student, Shokhruz Kakharov. Billions of years from now, Voyager will stay gravitationally bound to the Milky-Way. It will not be functional and behave like a technological asteroid, floating in interstellar space, passively kicked around under the influence of gravity, friction on an ambient medium or radiation pressure. Given that versions of our civilization may have existed billions of years ago around earlier Sun-like stars, their Voyager-like space trash could be all around us. Since their trash is our treasure, the fundamental question is how many such objects exist relative to natural icy rocks in interstellar space. This is crucial in assessing how easy it is to separate the `wheat’ of defunct technological objects from the `chaff’ of natural icy rocks.
The few interstellar objects that were discovered over the past decade: IM1, `Oumuamua, and Borisov, are consistent with roughly equal amount of total mass per logarithm of object mass. This would suggest that there are a million meter-size objects like IM1 for every 100-meters-size object like `Oumuamua. And if `Oumuamua followed a random passive trajectory, then there should be a quadrillion (10 to the power of 15) objects like it in the outskirts of the Solar system, half-way to the nearest star. Which fraction of them could plausibly be technological in origin?
`Oumuamua was somewhat larger than the size of Starship, the biggest rocket produced by humanity thus far. If humanity is in the middle of its lifespan of a few million years, and it will launch a new Starship-size spacecraft every decade in its technological future, then we might pollute interstellar space with a total of a million `Oumuamua-size artifacts. If all habitable planets in the Milky-Way hosted a civilization that follows this behavior, then the number of 100-meter artifacts could be a million larger than that of Milky-Way stars. This brings the entire population of Starships to just about a billionth of the abundance of `Oumuamua-like objects.
This is a tiny fraction, as long as `Oumuamua was on a random orbit. However, if it aimed to visit the habitable zone around the Sun, then the fraction could be of order unity. But even in the case of defunct space trash, the number of artifacts could increase dramatically in case they self-replicated before dying, just like biological organisms. Self-replication is feasible for technological probes equipped with 3D printers and artificial intelligence. Humanity is yet to develop space probes which replicate themselves, but life-as-we-know-it already met this challenge of self-replication on Earth billions of years ago.
The Rubin observatory in Chile will start surveying the Southern sky in 2025 with a 3.2 gigapixel camera. It could potentially discover interstellar objects that are 100-meter in size every few months and many more objects of smaller size. The census of interstellar objects will allow us to figure out if there is any `wheat’ among the abundant `chaff’.
Today, I had the privilege of watching the remarkable 2023 film “Postcard from Earth” in Las Vegas. The interstellar astronauts in this fictional storyline recap the history of life on Earth, from the earliest single-cell organisms to humans and the environmental catastrophe that their technologies inflicted, triggering a voyage to the stars with rare visits back to the home planet. Indeed, as described in my latest book “Interstellar”, becoming an interstellar species is a natural end state of intelligent civilizations. The film director, Darren Aronofsky, shot the film in the most visually-impressive locations on Earth with a state-of-the-art 18K resolution camera. Nevertheless, the number of pixels displayed in the film is still an order of magnitude below the resolution expected from the Rubin Observatory camera. Even though most of Rubin’s pixels will be dark, the rare bright ones illuminated by interstellar objects would be particularly exciting.
What are the questions that Rubin’s postcards of interstellar objects can address? The most pressing question is which fraction of all interstellar objects near Earth constitute technological space trash. The second question is which fraction of the technological objects are still functional devices. This fraction, as small as it might be, could inspire us to reverse-engineer alien technologies and use them to our benefit. Such an opportunity would raise legal questions: Should individuals benefit financially from imitating alien technologies or should all information from interstellar space be shared, like other astronomical data, with all humans? Do governments have the authority to classify related data and use it to their military advantage?
My hope is to witness a piece of alien technology during my lifetime. If I owned all the money in the world, I would have spent it on this search. But so far, my research funds within the Galileo Project include only a few million dollars to conduct the search. This is a millionth of the annual military expenditure worldwide. Does the search for a possible cosmic partner merit a millionth of the resources allocated by humans to the goal of killing each other? Are we truly an intelligent species?
If the U.S. Government happens to have relevant evidence, they could save me time by sharing the information with scientists like myself. I would love to get involved if related details surface in future congressional hearings on Unidentified Anomalous Phenomena (UAP). In the meantime, the Galileo Project observatories will continue to collect data on UAP in their search for extraterrestrial technological gadgets.
In the spirit of the upcoming Halloween holiday, the brilliant Galileo team member Eric Masson asked me whether we could play `trick or treat’ with UAP, attracting them to interact with our observatories. Here’s hoping that the extraterrestrial visitors at our doorstep will not wear scary costumes.
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.
