As I woke up for my morning jog before sunrise, I read an email from my dear colleague and friend, Frank Laukien, with a news report about two weird meteorites analyzed by a team led by Jennifer Mitchell, an electron microprobe lab manager at the University of Minnesota. After reading the details of the report, I wrote an email to Jennifer:
“Dear Jennifer,
I just read with great interest several news reports (here and here) about your analysis of the misfit meteorites NWA 15915 and Ksar Ghilane 022, as mentioned in the 2025 Lunar and Planetary Science Conference in Texas.
Interestingly, the estimate for the fraction of misfit meteorites, 0.2%, matches my estimate for the fraction of interstellar meteorites that originate outside the solar system. I derive this estimate from the abundance of meteors with a reported speed that is well above the escape speed of the Solar system in the CNEOS catalog of NASA for meteor fireballs. The data on one of these reported meteors (detected on May 8, 2014) indicates a speed that was well above the escape speed, as analyzed in the discovery paper here and in an independent study by the U.S. Space Command reported here. We analyzed meteoritic materials from the fireball site here. A second interstellar meteor from March 9, 2017 was reported in another paper here. These are two meteors out of 1,022 entries in the CNEOS fireball catalog. The statistics implies a probability of order (2/1,022) which is 0.2%, exactly the number for outliers among meteorites!
In a theoretical paper here, we suggested a possible origin for these interstellar meteors out of rocky planets that arrive close to dwarf stars and get tidally disrupted. During the close approach, their crust gets spaghettified into a stream of molten lava, with half of the material ejected to interstellar space. Dwarf stars with ~10% of the mass of the Sun are the most common type of stars. Your suggestion of a Mercury-like origin might be consistent with this process.
Following the two interstellar meteors in the CNEOS catalog, I suggested in various writings that one could search among collections of meteorites for the 0.2% outlier fraction of them that might be of interstellar origin. My suggestion is that the misfit meteorites NWA 15915 and Ksar Ghilane 022 originated from another star.
The coincidence of an outlier fraction of 0.2% which matches the estimate for the fraction of interstellar meteorites is tantalizing. Moreover, the tidal disruption of close-in rocky planets by dwarf stars, offers a natural association with a Mercury-like origin.
Let me know what you think.
Avi”
The preliminary report from Jennifer’s team is available here. Both NWA 15915, discovered in Algeria (with NWA referring to Northwest Africa), and Ksar Ghilane 022, discovered in Tunisia, were found in 2023, the same year when I led an expedition to the Pacific Ocean to retrieve materials from the 2014 interstellar meteor. Whereas our expedition retrieved only tens of milligrams of meteoritic materials, these two meteorites are 2.84 and 50 kilograms in mass, respectively. Jennifer’s analysis of NWA 15915 with an electron microprobe revealed that this meteorite contains a unique mixture of metal-rich minerals with magnetic properties formed in an environment with little oxygen, similarly to Mercury’s environment. The mineral crystals are large, indicating slow cooling and a large differentiated body — again suggesting Mercury-like conditions. However, the detailed findings imply that the origin is not Mercury itself. Ksar Ghilane 022 has similar characteristics but different magnetic properties.
Did the misfit meteorites NWA 15915 and Ksar Ghilane 022 originate from a planet that was ejected from the early solar system or were they produced near other stars? Analysis of their isotopic composition could clearly distinguish between these two possibilities. Given their large mass, isotope analysis should be straightforward.
Science is exciting as it is guided by evidence, which holds the potential of surprising us with misfits. Outliers are the key for discovering something new. They are often brushed under the carpet of traditional thinking, but every now and then there is a brilliant experimentalist like Jennifer who reports about them. Are 0.2% of all meteorites of interstellar origin? Time will tell.
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.
