Seeking the Second Interstellar Meteor

Avi Loeb
4 min readFeb 22, 2024

While working on the first interstellar meteor IM1 detected by US Government satellites, I received generous support from the Office of Science and Technology Policy at the White House which reached out to the US Space Command, leading to an official confirmation letter on the interstellar origin and fireball light curve of IM1. This allowed my research team within the Galileo Project to proceed with a related expedition to the Pacific Ocean in search for the materials left over from IM1’s fireball.

The official letter and data from the Department of Defense allowed us to receive funding and visit IM1’s site, where we recovered spherules of potentially extrasolar composition. Our findings were recently published in two research notes and summarized in an extensive paper.

We are currently in the process of planning our next expedition. One possibility is to visit the site of the second interstellar meteor, labeled IM2. Its fireball released ten times more energy than IM1, amounting to a fifth of the energy output of the Hiroshima atomic bomb. IM2 was reported to have a geocentric velocity vector of (−15.3, 25.8, −20.8) kilometers per second when it exploded in two flares at 40.5° N18.0° W and an altitude of 23 kilometers, on March 9, 2017, 04:16:37 UTC, as reported in the CNEOS catalog of meteor fireballs compiled by NASA’s Jet Propulsion Laboratory.

Upon entering the solar system, IM2’s velocity was 40 kilometers per second relative to the Local Standard of Rest of the Milky-Way galaxy, making it faster than most stars in the vicinity of the Sun. As with IM1, the material strength of IM2 was higher than almost all solar system meteorites in the CNEOS fireball catalog, including those made of iron. This suggests a differentiated material composition as we identified for IM1, potentially caused by the tidal disruption of magma-ocean planets by dwarf stars, as argued in a recent paper that I published with my postdoc Morgan MacLeod.

For the second interstellar meteor IM2, our goal would be to collect not just millimeter-size spherules but much bigger pieces of the object with enough material to allow three exciting breakthroughs:

1. Identify the solid-state structure and nature of the object.

2. Identify all the elements that made it, including volatile elements which are lost for spherules during an airburst.

3. Date the age of the object from isotopes such as Uranium-238 (half-life of 4.5 billion years, equal to the age of the solar system) and Thorium-232 (half-life of 14 billion years, equal to the age of the Universe). Knowing the age and the velocity vector would allow us to figure out where the object came from, since we can integrate its trajectory back in time.

Based on the fireball energy, IM2 had a diameter of order a meter, similar to the meteor BX1 which was spotted on January 21, 2024 over Berlin. The discovery of centimeter-scale fragments weighing between 1 and 100 grams from BX1, lends hope that we could recover similarly large pieces from IM2. Seeking these materials would be more challenging than in IM1’s expedition, because the ocean is a few times deeper and the ocean floor is more rugged at IM2’s site. But as with dating, challenges make any finding more exhilarating.

Experimental science is exciting, like a detective story. As Arthur Conan Doyle stated in the words of his fictional detective Sherlock Holmes: “Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.”

Yesterday, I was contacted by one of my favorite actors, Paul Giamatti, who follows my research with great interest and invited me to a conversation on his podcast. Paul portrayed beautifully an aging teacher in his latest film, The Holdovers. His invitation was a timely gift for my 62nd birthday in just a few days. The time is ripe for me to make my final act. Throughout my forty years as a theoretical physicist, I drank from the firehose of ideas that constantly bubble up in my head. But over the past five years, I decided to lead experimental work and test the most improbable of these ideas: that some of the interstellar objects that arrive near Earth might be of technological origin. If my research team discovers clear evidence for a Voyager-like meteor, I will feel that I have arrived at the Promised Land after forty years of wandering through the desert, just like the Israelites in the biblical story of exodus.


Image credit: Chris Michel (October 2023)

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, and 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.



Avi Loeb

Avi Loeb is the Baird Professor of Science and Institute director at Harvard University and the bestselling author of “Extraterrestrial” and "Interstellar".