On February 8, 2024, at 23:48:00 local time, the Subaru-Asahi Star Camera at the Maunakea Observatory in Hawaii, owned by the National Astronomical Observatory of Japan, recorded a video of a meteor fireball blazing across the night sky. The object that burned in the Earth’s atmosphere was identified as a reentering Chinese satellite named Object K. This name sounds Kafkaesque. But sticking to the dry facts, Object K’s fireball represents Nature’s way of cleaning up human-made space trash.
Not all human-made space trash is eliminated so quickly. For example, Elon Musk’s Tesla Roadster, which was launched into space as a dummy payload on the Falcon Heavy test flight in 2018, will continue on an elliptic orbit around the Sun for tens of millions of years. Computer simulations of the Tesla Roadster’s orbit in the next 15 million years show 22%, 12%, and 12% of the orbit realizations impacting the Earth, Venus, and the Sun, respectively. Musk’s space trash will eventually be cleaned up within a time period comparable to the 66 million years that elapsed since non-avian dinosaurs were killed by the impact of the Chicxulub meteorite. Nature will eventually take care of cleaning up the Tesla Roadster, and so far, no courtroom has fined SpaceX for polluting interplanetary space, the way companies are fined for trashing public spaces.
The prospects for a natural clean-up get worse when dealing with humanity’s pollution of interstellar space. The interstellar probes Voyager 1, Voyager 2, Pioneer 10, Pioneer 11, and New Horizon will exit the Oort cloud at the edge of the solar system within 10 thousand years. At that time, these technological objects would constitute defunct space trash. The chance that any of these interstellar objects will collide with a star or a planet in the entire Milky Way galaxy within ten billion years is less than a part in a billion.
But if humans were to change their priorities and invest in space exploration instead of killing each other, this statistic would change. If the worldwide military budget of 2 trillion dollars per year would be invested in launching CubeSats to interstellar space, then within a century, we could guarantee that some of these gadgets will crash into an exoplanet or a star. Whether it would be noticed by exo-astronomers is a different matter.
Suppose the extraterrestrials share the dullness of earthlings. In that case, they are likely to conclude that a Tesla Roadster passing near their planet is a rock of a type never seen before, most likely a hydrogen iceberg, a nitrogen iceberg, or a dust bunny. And regarding our CubeSat that crashes on their planet, they might say that any spherules retrieved from the crash site are likely coal ash of their own.
But there is also hope that some of our neighbors out there are more advanced. In that case, our pollution of interstellar space might be corrected by a civilization that has empathy for our primitive state of mind and feels responsible for maintaining a clean cosmic neighborhood.
The short video captured by the Subaru camera shows another meteor that flies perpendicular to Object K. Is this coincidence expected over the short 2:21 minute duration of the Subaru video? My brilliant collaborator, Dani Maoz, noted that the Alpha Centaurid meteor shower peaked in the Southern hemisphere on February 8-9 with up to six meteors per hour. This implies that over 2:21 minutes, there is a significant 24% chance of seeing one of these Alpha Centaurids.
An interesting question is how frequently do we see interstellar meteors that originated outside the solar system, and what fraction of those are technological, like Object K, rather than natural, like the Alpha Centaurids? NASA’s CNEOS catalog of fireballs suggests that meter-scale objects from interstellar space impact the Earth roughly once per decade.
In recent days, I worked day and night on an extended paper that summarizes our findings from the Pacific Ocean site of the first recognized interstellar meteor, IM1, whose fireball was spotted by US Government satellites on January 8, 2014, exactly a decade ago. About a tenth of the 850 spherules that our expedition team recovered showed a unique chemical composition of elements that were not reported before for solar system rocks. In order to learn more about the nature of IM1, we are planning a second expedition that will seek larger pieces of the bolide, similar to those found from the similar-size meteor BX1 that exploded over Berlin, Germany, on January 21, 2024.
During a public lecture that I gave a couple of days ago at the Astronomy Club in Santa Monica, I was asked whether old meteorite samples can be searched for interstellar objects. I replied that finding large fragments of IM1 would allow us to flag the properties that distinguish interstellar objects from solar system meteorites and search for these properties in existing collections of meteorites.
To find larger fragments of IM1, our next ocean expedition will use a video feed and a remotely operated vehicle (ROV). These tools will likely place a price tag of 5 million dollars on the mission. We welcome potential donors who are interested in joining us on our next interstellar expedition.
Humanity’s search for interstellar objects could extend well beyond Earth and its atmosphere. For example, the Moon does not have an atmosphere so its surface collected interstellar impactors over 4.5 billion years. Once we settle on the ancient museum floor of the lunar surface, we could survey the local display of impactors and search for interstellar objects like IM1’s fragments. Any technological trash from extraterrestrials would be our treasure.
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 chairs the advisory board for the Breakthrough Starshot project. 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. His new book, titled “Interstellar,” was published in August 2023.