On November 5, 2025, astronomers unveiled two new images of the intriguing interstellar object 3I/ATLAS. These images reveal a compact source of light, yet surprisingly, there is no clear cometary tail visible. The morphology of the coma appears similar to its earlier observation made by the Hubble Space Telescope on July 21, 2025. This consistency is unexpected, especially in light of a recent report from NASA's Jet Propulsion Laboratory (JPL), highlighting non-gravitational acceleration observed in 3I/ATLAS.
The JPL report details specific acceleration metrics, normalized at a heliocentric distance of 1 astronomical unit (au). Notably, it indicates 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. According to momentum conservation principles, it has been calculated that the mass loss during 3I/ATLAS's perihelion passage exceeds 13%. Typically, such a significant mass loss would lead to a pronounced coma, complete with dust and gas that would naturally form a cometary tail directed away from the Sun. However, the latest images do not support this expectation.
For context, a recent image of the solar system’s comet Lemmon, captured just two days prior, clearly displays a cometary tail pointing away from the Sun, as would be anticipated. This stark contrast raises questions about the anomalies observed in 3I/ATLAS, which include a range of intriguing characteristics.
The peculiarities of 3I/ATLAS include:
Retrograde Trajectory: The object’s retrograde path is closely aligned with the ecliptic plane, with a likelihood of just 0.2%. Sunward Jet: In July and August 2025, it exhibited a sunward jet (or anti-tail) that is not merely an optical illusion, distinguishing it from typical comets. Massive Nucleus: Its nucleus is approximately a million times more massive than 1I/`Oumuamua and a thousand times more than 2I/Borisov, while traveling at a speed greater than both, with a likelihood of less than 0.1%. Fine-Tuned Arrival: The trajectory was adjusted to pass within tens of millions of kilometers from Mars, Venus, and Jupiter, remaining unobservable from Earth at perihelion, with a likelihood of 0.005%. Gas Composition: Its gas plume contains significantly more nickel than iron, with a nickel to cyanide ratio far exceeding that of known comets, including 2I/Borisov, with a likelihood below 1%. Low Water Content: The gas plume consists of only 4% water by mass, a stark contrast to typical comet compositions. Extreme Polarization: It displays unprecedented extreme negative polarization, with a likelihood below 1%. Directional Arrival: The object arrived from a direction closely aligned with the radio “Wow! Signal” to within 9 degrees, with a likelihood of 0.6%. Rapid Brightening: Near perihelion, 3I/ATLAS brightened faster than any known comet and exhibited a color bluer than the Sun. Massive Evaporation: The observed non-gravitational acceleration suggests substantial evaporation of at least 13% of its mass, although preliminary post-perihelion images have yet to show evidence of this.This afternoon, I received an inspiring email from Dario Villalón, a civil electrical engineer from Santiago, Chile. Dario shared how the research on 3I/ATLAS has sparked interest in astronomy and astrophysics among ordinary people. He expressed gratitude for the work being done, noting that his 18-year-old daughter, who was uncertain about her career path, has become motivated to explore studies in these fields due to your publications and insights.
Dario's message underscores the importance of scientific communication and its role in inspiring the next generation of scientists. His encouragement to continue this important work amidst challenges reflects a broader sentiment shared by many who follow these remarkable discoveries.
The ongoing research into 3I/ATLAS continues to reveal unexpected findings, challenging our understanding of interstellar objects and comets. As we await further observations and discoveries, the excitement surrounding this enigmatic object only grows.
