Over the past two weeks, I have circumnavigated the globe by land, air and sea. The reason? A kitchen sink–sized chunk of interstellar material that my colleagues and I believe collided with the Earth at 100,000 miles per hour nearly a decade ago. After years of effort, we may have finally found pieces of this elusive object on the bottom of the Pacific Ocean, about a mile beneath the waves.
The story began in April 2019, when I found what’s thought to be the first known interstellar meteor, hiding in plain sight in publicly accessible data sourced from the U.S. government. Called IM1, this object had burned up in the atmosphere and rained fragments down into the ocean off the coast of Manus Island, Papua New Guinea, five years prior, registering as an anomalously speedy and bright fireball in the sensors of secret spy satellites operated by the U.S. Department of Defense. Working with my then-adviser, the Harvard astrophysicist Avi Loeb, I analyzed the U.S. government data to show how the trajectory and other properties of IM’s fireball were consistent with the meteor having an interstellar origin.
It seemed at first too good to be true; scientists had been searching for interstellar meteors for at least seven decades, and here I was, a sophomore in college sitting in my dorm room, thinking I’d bagged one. And sure enough, there was a catch—but it had nothing to do with my calculations. Because the data came from spy satellites, the U.S. government didn’t publish how precise the measurements were. And without knowing the level of precision, we couldn’t know for sure whether IM1 was truly interstellar, or just a fluke.
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It took three years for U.S. government officials to publicly confirm that their satellite data supported our interstellar hypothesis for IM1. While I was waiting, I dreamed of searching the ocean floor for fragments of the object, and to learn more I reached out to the only team to ever go after submarine meteoritic material from an observed meteor fall. It turned out that the mile-deep water at the most likely region where IM1’s debris fell would be advantageous, as the relative inaccessibility of such depths would ensure the fragments remained unperturbed. So once official confirmation arrived, planning for an ocean voyage to 1.3S, 147.6E began in full force.
To say we were looking for a needle in a haystack would be a profound understatement; seeking tiny pieces of a meteor on the seafloor is actually much harder. But much like a steel needle (and unlike most ocean-bottom debris), meteoritic fragments tend to contain ferrous material. This means many of the pieces should stick to magnets. So our strategy was simple: drag a magnetic sled across the seafloor within IM1’s projected debris field in the hopes of recovering some fragments. Finding even one would be a historic discovery, representing the first time humanity knowingly came into direct contact with material from another planetary system. Much like the discovery of the first exoplanet, the discovery and study of the first interstellar meteorite would open up new scientific vistas in which we might more clearly see and understand our own cosmic context, revealing otherwise-hidden details about the coalescence of stars and planets elsewhere in our galaxy.
In the months leading up to the expedition, which would take place aboard a ship called the Silver Star, I focused on the scientific planning while Avi concentrated on funding and logistics. Using archival seismic data from terrestrial instruments that had picked up the sonic boom from IM1’s fireball, I was able to pin down the resulting debris field to some 50 miles offshore of Manus Island, in an arc of open water seven times smaller than the area provided to us by the Department of Defense. This localization would allow for a chance, albeit slim, of success in realizing my dream of holding a piece of history—a bona fide interstellar object—for the very first time.
Fifty hours after departing from my sister’s wedding in the English countryside, I arrived at Manus Island, where our dear expedition vessel, Silver Star, was filled with a world-class team to make my dream a reality. While I was in England, the expedition team had already found some interesting and varied human-made debris, including wires and steel shavings.
When I boarded Silver Star, the search hadn’t yielded potential interstellar material yet. This wasn’t surprising, since we were trying to find a needle in the world’s most unforgiving haystack. Much of the search up until that point had been motivated by an effort to find relatively big fragments: ones millimeter-size or larger. Millimeter-size fragments would be easier to find than sub-millimeter ones, plus they would carry more mass. But I reminded the team that to be successful we needed to be searching for even smaller needles—ones that might not be visible to the naked eye. The smaller the pieces, the greater the abundance. The greater the abundance, the higher the chance of finding a fragment of IM1. Specifically, this meant sharpening our focus on finding material in a size range of 10–700 microns, corresponding to the sizes of the tiny drops of molten metal that cool into spheres as they rain down from metallic meteors. Within two hours of my arrival, we had recovered one such spherule, a few hundred microns in size, from a sample collected along the strip that I had calculated to be the most likely airburst location for IM1. We immediately began hunting for more.
At the expedition’s conclusion, our final count was a whopping 50 spherules, ranging in size at 100–700 microns, with the plurality coming from the search strip I calculated. Detailed analysis with state-of-the-art instrumentation should yield an even higher count and a smaller size threshold.
These spherules are tantalizing, especially given that many of them show compositional anomalies relative to typical ones. Could some of them represent the first material ever recovered from an interstellar object? Or do they belong to the background population of spherules from “local” solar system meteors, which have accumulated on the seafloor over geological time? Or were they produced by humans, through high-temperature processes like welding?
A definitive answer will emerge from studying the isotopic signatures embedded within the spherules. Compared to spherules from run-of-the-mill meteorites, an overabundance of rare isotopes (or an underabundance of common isotopes) in the ones collected from our search region would be compelling evidence for IM1’s interstellar origin. This isotopic analysis is currently underway at the University of California, Berkeley, and will soon begin at Harvard University.
The discovery of material from an interstellar meteor would be an enormous scientific achievement. To put it in context, an optimistic estimate for the time it would take to fetch a similar sample from the nearest star system is comparable to the age of our species. By contrast, nature may have delivered an interstellar gift to our cosmic doorstep, which has taken us less than a decade to retrieve.
As we await the results of isotopic analysis of IM1, one thing is for sure: Even if we don’t find anything, the experience of having searched in the first place will inform our next mission to find material from another interstellar candidate: the more massive IM2, which created a conspicuous fireball of its own off the coast of Portugal in March 2017. With careful planning and a bit of luck, sooner or later we should uncover the cosmic secrets contained in the fragments of interstellar messengers.
This is an opinion and analysis article, and the views expressed by the author or authors are not necessarily those of Scientific American.