We are currently planning a second expedition to the Pacific Ocean in search for bigger pieces of the first identified interstellar meteor, IM1. The first expedition to IM1’s site, as localized by sensors aboard U.S. Government satellites, recovered submillimeter-scale spherules with a chemical composition that is different from known solar system materials.
The interstellar origin of IM1 was originally based on its high speed. The unfamiliar composition adds support to this identification. But a follow-up mission to recover bigger pieces is needed in order to learn more about IM1. What can we hope to learn?
Most importantly, the core of IM1 may have survived the fireball and landed on the ocean floor. The first expedition used a sled with small magnets that could not retrieve a large relic body from IM1. The use of a Remotely Operated Vehicle (ROV) with a large retrieval apparatus and a video feed would help us find and collect the biggest piece left over from IM1’s wreckage. This finding would nail the nature of the parent object.
Second, finding large pieces would allow us to measure the unusual material strength of IM1. The spherules that were recovered in the first expedition were composed of molten material that lost its original material properties after being exposed to the immense heat from the friction of IM1 on Earth’s lower atmosphere. The light curve of the fireball showed three successive detonations separated by a tenth of a second from each other, with the last flare being the brightest and at a ram-pressure of 200 megapascals. This stress is four times higher than the maximum ram-pressure up to which the toughest iron meteorites from the solar-system survive. Indeed, IM1 displayed the highest material strength among all meteors in the CNEOS fireball catalog of NASA/JPL.
In addition to enabling a measurement of IM1’s material strength, finding bigger pieces would allow us to gauge other material properties of IM1, such as the heat conduction coefficient and the electric conductivity. When combined, these measurements could be used to test a possible origin from a magma ocean of a tidally disrupted planet against the alternative of a Voyager-like meteor.
The recovered spherules lost volatile elements as their material melted when it was heated to a high temperature by the fireball. However, bigger pieces could have retained the volatile elements in their cores — which were not exposed directly to the fireball. Studying these cores would allow us to get a full census of the chemical composition of IM1, including the decay products of radioactive isotopes. In particular, the detection of lead isotopes (Pb-206, 207 and 208) as the decay products of uranium (U-235 and 238) and thorium (Th-232) isotopes, could be used to derive an age for IM1’s material and differentiate it further from solar system materials for which the age is well measured at 4.57 billion years.
The large amount of material in bigger IM1 fragments would also enable us to find other rare isotopes and look for anomalies relative to their solar system abundances.
Altogether, recovery of large IM1 pieces would constitute the first time that scientists put their hands on unprocessed materials from a large object (much bigger than micron-size interstellar dust particles) that came from outside the solar system. The discovery can educate astronomers of what happens around other stars. It would take our spacecraft more than 50,000 years to reach the environments surrounding the nearest stars. We can save on wait time by studying objects like IM1 which already made the reverse trip from these environments to Earth.
Upon entering the solar system, IM1 moved with an interstellar velocity of 60 kilometers per second relative to the Local Standard of Rest of the Milky-Way galaxy, making it faster than 95% of the stars in the vicinity of the Sun. To obtain a speed of this magnitude, a rock must get twice as close to the Sun as Mercury, the innermost planet in the solar system.
IM1’s extremely high speed and material strength suggests an exciting origin, different from what we are familiar with in our backyard. Perhaps it is the product of spaghettification of a rocky planet by a dwarf star, or perhaps it is something else. As I told a reporter earlier today: “Science is done by iterations. Data collection is driven by curiosity. Those who pretend to know the answers in advance are not following the scientific method.”
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. His new book, titled “Interstellar”, was published in August 2023.
