The IM1 Interstellar Meteor Spherule Expedition

8 January 2014. 17:05:34 UTC. Over the Bismarck Sea, north of Manus Island in Papua New Guinea, a small, very fast fireball entered the atmosphere. US government sensors recorded it. NASA and JPL listed it in the CNEOS fireball database as CNEOS 2014-01-08. It was about 0.45 metres across. It reached peak brightness at 18.7 km altitude and eventually broke up over the South Pacific Ocean.

In 2019, Harvard undergraduate Amir Siraj and astronomer Avi Loeb looked at its catalogued entry speed of 44.8 km/s. Siraj said it seemed "to come from a hyperbolic orbit coming from another star system." They named it IM1, the first known interstellar meteor. The peer-reviewed paper appeared in 2022. That year a US Space Command memo to NASA stated that "the velocity estimate reported to NASA is sufficiently accurate to indicate an interstellar trajectory."

14 June 2023. Loeb's Galileo Project expedition sailed from Lorengau, Manus Island, aboard the Silver Star. Data from a nearby seismometer had narrowed the search to about 16 square kilometres, inside a Department of Defense localization box of about 120. Loeb called the task "finding a needle in the ocean."

The team dragged a magnetic sled across the seafloor, about 2 km down. 26 sled runs covered more than 175 km of search lines. On 20 June the first spherules came up. They measured about 0.3 mm across. Loeb described them as "mostly iron with some magnesium and titanium but no nickel."

The count kept growing. First 11. Then 25. Then more than 50. The August 2023 preprint reported about 700. A subset, which the team called BeLaU, was enriched in beryllium, lanthanum and uranium by up to "three orders of magnitude relative to the solar system standard." The team wrote of "a highly differentiated, extremely evolved composition of an unknown source." Loeb said publicly that a technological origin could not be ruled out. "It's the first time that humans are holding in their hands material from a big object that came from interstellar space," Loeb told NewsNation.

Some critics went after the speed. Vaubaillon called its anomalous properties "better described as measurement error." Brown and Borovička found the light curve fit a stony body about 20 km/s slower. Peña-Asensio and colleagues found "no evidence for interstellar fireballs in the CNEOS database."

Then the seismic clue. Benjamin Fernando and colleagues found the signal "changed directions over time, exactly matching a road that runs past the seismometer." It was, they concluded, a passing truck. "The signal Harvard used to locate the impact is totally bogus," said Göran Ekström of Lamont.

The spherules drew fire too. Gallardo proposed coal ash. Desch and Jackson argued they were ordinary spherules altered by long exposure on the seafloor, with iron isotopes that excluded an extrasolar origin. Desch later proposed microtektites from the Australasian tektite strewn field, created 788,000 years ago by an impact in Indochina. Loeb pushed back. Critics, Loeb said, "did not collect material, they did not analyze anything."

"For all of the naysayers, I would say this is exactly the way science should be working," Loeb said. The book Interstellar followed in August 2023, and a documentary crew directed by Jason Kohn filmed aboard the Silver Star. A return trip with a remotely operated vehicle was planned for summer 2025. Then, in September 2026, a calibration study of CNEOS speeds found that the 2014 event "remains the largest-margin catalogue entry" among 7 nominally hyperbolic events. The speed question, at least, is back on the table.