The Remarkable Large-Scale Structure of Anti-Tail and Tail Jets from 3I/ATLAS | by Avi Loeb | Nov, 2025

Comet’s Dual Jets Challenge Existing Theories of Solar System Formation

CAMBRIDGE, MA – November 2025 – A newly observed⁤ comet,⁣ 3I/ATLAS⁤is⁢exhibiting⁣anunprecedentedstructuralanomaly-aprominent”anti-tail“‌pointingtoward the sun alongside its expected tail extending away – forcing astrophysicists to re-evaluate current understandings of cometary behavior ⁢and perhaps, the early solar system’s evolution. The findings, spearheaded by⁣ Avi Loeb, head of the Galileo ​Project and a ‌Harvard‍ University astrophysicist, reveal a complex​ interplay of ‌dust and gas ‍dynamics⁤ unlike anything ⁢previously documented.

The unusual structure of 3I/ATLAS,‍ first detected in early 2023 and currently visible with binoculars, suggests the comet is comprised of two distinct dust populations, each responding differently to solar radiation and the comet’s own outgassing. This discovery isn’t merely an oddity; it provides a rare window into the composition and internal structure of a pristine comet originating⁣ from the Oort cloud,⁢ the solar system’s distant reservoir of icy bodies. Understanding these structures can illuminate the ⁣conditions present during the formation of‍ planets and the delivery of water and organic molecules to early Earth.

Loeb, also founding director of Harvard University’s Black Hole Initiative, and his team analyzed ⁢images of 3I/ATLAS revealing a shining, sun-facing “anti-tail”⁤ composed of dust⁢ grains released⁣ earlier in the comet’s journey. These larger particles, less susceptible to solar wind ⁣pressure, follow a ballistic trajectory, appearing to lag behind the comet ​as it moves toward‍ the sun. Together, a⁣ more typical tail, composed of finer dust and gas, is being pushed away by solar radiation and the solar wind.

“This is a stunning display of cometary physics,” explains Loeb. “The anti-tail demonstrates that the comet is not ⁣just a passive snowball, but a complex object with a history etched into its dust composition.”

The comet’s dual-jet structure was initially observed in September 2023, and subsequent observations have refined the understanding of the differing particle⁣ behaviors. The anti-tail is expected to become more prominent as 3I/ATLAS approaches perihelion – its closest approach to the sun – in⁤ late september 2024.

Loeb is the author of Extraterrestrial: The First Sign of Smart Life beyond Earth (2021) and Interstellar (2024), and a former ‍chair of the astronomy department ‍at Harvard University. His research continues to focus on unraveling the mysteries of the cosmos, from the search for extraterrestrial life to the origins of our own solar system.

(Image Credit: Chris Michel, National Academy of⁢ Sciences, 2023)