Interstellar Object 3I/ATLAS displays Unexpected Jet Structure Post-closest Approach to Sun
CAMBRIDGE, MA – November 2025 - A recently observed interstellar object, 3I/ATLAS, is exhibiting a complex jet-like structure emanating from its nucleus after passing its closest point to the sun (perihelion), a finding that challenges existing models of cometary activity and interstellar object behavior. The findings, led by Avi Loeb, head of the Galileo Project at Harvard University, suggest a previously unknown mechanism at play in the composition and fragmentation of these celestial visitors.
The unexpected jet structure, observed following 3I/ATLAS’s perihelion passage in late September 2025, indicates a more active and volatile composition than initially anticipated for an interstellar object. This observation is particularly meaningful as it provides a rare prospect to study material originating from outside our solar system, potentially offering clues about the formation and evolution of planetary systems beyond our own. Understanding the processes governing the behavior of interstellar objects is crucial for assessing potential risks and unraveling the mysteries of the universe’s building blocks.
Loeb, also the founding director of Harvard University’s Black Hole Initiative and director of the Institute for Theory and computation at the Harvard-Smithsonian Center for Astrophysics, detailed the observations and their implications. “The jet structure is not what we typically see in comets originating from our solar system,” Loeb explained. “Its complexity suggests a unique internal composition and a different mechanism driving its activity,potentially related to subsurface volatiles exposed by solar heating.”
3I/ATLAS was first discovered in June 2023 and quickly identified as an interstellar object due to its highly hyperbolic orbit. Its trajectory brought it within approximately 120 million miles of the sun, a close approach that triggered increased activity. Observations following perihelion revealed the distinct jet-like features, prompting further inquiry by Loeb and his team.
Loeb is the author of Extraterrestrial: The First Sign of Bright Life Beyond earth and Interstellar,published in 2021 and August 2024 respectively,and a co-author of the textbook Life in the Cosmos. The Galileo Project, which he leads, is dedicated to searching for evidence of extraterrestrial technological signatures and studying interstellar objects like 3I/ATLAS. Further analysis of the data is underway, with researchers hoping to determine the precise composition of the jet material and gain a deeper understanding of the object’s origins and internal structure.
