No Clear Cometary Tail in Post-Perihelion Images of 3i/atlas

The Intriguing Case of 3I/ATLAS

The interstellar object known as 3I/ATLAS has been a subject of intense scrutiny since its discovery. Recent observations, specifically post-perihelion images taken on November 5, 2025, have raised new questions about the nature of this celestial body.

No Clear Cometary Tail Observed

On November 5, 2025, two new images of 3I/ATLAS were released. These images show a compact source of light without a clear cometary tail. The Sunward direction is towards the bottom left corner, as indicated by an arrow on the image provided.

The coma (the fuzzy halo around a comet) does not display any significant difference in morphology compared to its appearance in the Hubble Space Telescope on July 21, 2025.

Avi Loeb, who has been closely monitoring this object, notes that these observations are surprising given NASA’s JPL report which indicates non-gravitational acceleration in 3I/ATLAS. The report states a radial acceleration away from the Sun of 1.1 x 10^-6 au per day squared and a transverse acceleration relative to the Sun’s direction of 3.7 x 10^-7 au per day squared.

This non-gravitational acceleration suggests that the mass fraction lost during the perihelion passage is larger than 13%. For a typical comet, this amount of mass loss would result in a massive coma with dust and gas pushed away from the Sun by solar radiation pressure and solar wind. However, no such tail is visible in the new images.

Comparison with Known Comets

The absence of a cometary tail in 3I/ATLAS has led to comparisons with known objects like Lemmon, an interstellar comet observed by the R. Naves Observatory on November 3, 2025. The image shows a clear cometary tail away from the Sun, as expected from a typical comet.

Avi Loeb lists several anomalies displayed so far by 3I/ATLAS, including its retrograde trajectory aligned to within 5 degrees with the ecliptic plane of the planets around the Sun. Other notable anomalies include:

• Sunward jet during July and August 2025 that is not an optical illusion.
• Nucleus significantly more massive than other known interstellar objects like `Oumuamua and Borisov, moving faster with a likelihood of less than 0.1%.
• Arrival time fine-tuned to bring it within tens of millions of kilometers from Mars, Venus, and Jupiter without being observable at perihelion, with a likelihood of 0.005%.
• Gas plume containing much more nickel than iron, with an unusually high nickel to cyanide ratio compared to known comets.
• Gas plume containing only 4% water by mass, unlike familiar cometary compositions.

Impact of Avi Loeb’s Work: Inspiring Future Generations

The work of Avi Loeb has not only contributed to the scientific understanding of interstellar objects but also inspired many people. In a recent email from Chile, Dario Villalón, a civil electrical engineer from the University of Chile, expresses gratitude for Loeb’s research. He mentions that his 18-year-old daughter, who was previously unsure about her career path, has become interested in astrophysics and astronomy due to Loeb’s publications.

Villalón emphasizes the importance of Loeb’s work in motivating young individuals towards scientific fields. His daughter will likely pursue studies in this field, reflecting the broader impact of Avi Loeb’s research on future generations.

Conclusion

Ongoing Investigations

The absence of a cometary tail and other anomalies displayed by 3I/ATLAS continue to intrigue scientists and researchers. Avi Loeb’s ongoing investigations into these phenomena underscore the need for continued observation and analysis. As more data becomes available, the scientific community will be better equipped to understand the nature and origin of interstellar objects like 3I/ATLAS.