New Images Reveal 3I/ATLAS Anti-Tail Longer Than Earth-Moon Distance

New observations of the interstellar object 3I/ATLAS have revealed an unprecedented sunward-pointing anti-tail extending over 500,000 kilometers—surpassing the average distance between Earth and the Moon. The discovery, captured by multiple telescopes around the world, represents the largest anti-tail ever observed for any comet or interstellar object.

As of December 14–15, 2025, 3I/ATLAS was located approximately 270 million kilometers from Earth, approaching a perigee of 268.9 million kilometers on December 19, 2025. Images taken in Italy, California, and Thailand confirm a sunward anti-tail stretching roughly half a million kilometers from the comet’s nucleus.

“This distance exceeds the average lunar distance of 384,400 kilometers and represents the largest anti-tail observed for any comet or interstellar object to date,” experts say. Observations will continue to monitor the anti-tail’s evolution as the object moves away from Earth.

Observational Details

On December 15, a 0.25-meter telescope in Calabria, Italy, captured an image with a field of view of 0.86 by 0.39 million kilometers. Using a Larson-Sekanina rotational gradient filter, the anti-tail’s sunward extension of approximately 500,000 kilometers was clearly highlighted.

Earlier, on December 14, a 14-inch telescope in June Lake, California, produced a two-hour and 22-minute integrated image revealing a green-blue anti-tail spanning 4.24 million kilometers. Additionally, a 0.26-meter telescope in Rayong, Thailand, confirmed the feature on December 13, using rotational-gradient brightness mapping techniques. Observers credited include Toni Scarmato, Dan Bartlett, and Teerasak Thaluang.

Physical Properties and Scale

To extend 500,000 kilometers over 45 days post-perihelion, material in the anti-tail must travel at a minimum sunward speed of 130 meters per second relative to the nucleus. The tail consists of micrometer-sized dust or gas released from icy regions under solar radiation and the solar wind.

Peer-reviewed studies by Avi Loeb and Eric Keto suggest that the anti-tail may result from sunlight scattering by icy fragments or a swarm of small objects lagging behind the nucleus due to non-gravitational acceleration. Scientists continue to observe the object to refine models of particle release and interstellar dynamics.

Historical Context and Ongoing Monitoring

Anti-tails typically appear temporarily in solar system comets due to Earth crossing the comet’s orbital plane. However, for 3I/ATLAS, the anti-tail was first recorded in a Hubble Space Telescope image on July 21, 2025, at 2.98 AU from Earth, and it remained visible in subsequent images, including November 30 at 1.91 AU. This confirms that the anti-tail is a persistent feature rather than a perspective effect.

Ground-based and space-based observatories continue to track 3I/ATLAS, with observations near perigee on December 19, 2025, expected to provide further insights into the anti-tail’s structure, direction, and surface features. These ongoing studies aim to improve our understanding of interstellar objects and the complex processes that form anti-tails.

The dataset gathered from 3I/ATLAS is poised to become a critical reference for interstellar observations, helping scientists model particle release, non-gravitational acceleration, and other morphological features beyond the solar system.