Key Highlights
- The first evidence of a non-gravitational acceleration was observed in the interstellar object 3I/ATLAS at its perihelion.
- NASA’s Jet Propulsion Laboratory engineer Davide Farnoccia measured two components of this acceleration: radial and transverse, both relative to the Sun.
- The non-gravitational acceleration suggests that 3I/ATLAS could be losing mass due to ejection or an internal engine, with potential massive evaporation during its perihelion passage in November 2025.
Unusual Interstellar Object 3I/ATLAS
The discovery and subsequent observations of the interstellar object 3I/ATLAS have puzzled astronomers since its detection. Recently, a significant finding has been reported by Davide Farnoccia, a navigation engineer at NASA’s Jet Propulsion Laboratory in Pasadena.
Non-Gravitational Acceleration: Evidence and Measurement
Farnoccia’s report, filed on October 29, 2025, at the object’s perihelion distance of approximately 1.36 astronomical units (AU), revealed a non-gravitational acceleration that deviates from expected gravitational forces alone.
The measured acceleration had two components: a radial component away from the Sun of 135 kilometers per day squared and a transverse component relative to the Sun’s direction of 60 kilometers per day squared. These findings suggest potential propulsion mechanisms, such as thermal ejection or an internal engine, which could explain the object’s unusual behavior.
Implications for 3I/ATLAS
The non-gravitational acceleration implies that if propelled by ejecting gas, 3I/ATLAS would lose a significant portion of its mass. For instance, with an estimated thermal ejection speed of a few hundred meters per second, the object could lose about half its mass over six months.
This rapid loss in mass is predicted to be observable as a large plume of gas surrounding 3I/ATLAS during November and December 2025. ESA’s Juice spacecraft will detect this change starting early November, while ground-based telescopes and Hubble and Webb space telescopes will have the best opportunity to observe these phenomena when 3I/ATLAS reaches its closest approach to Earth on December 19, 2025.
The non-gravitational acceleration also correlates with an unusual brightening of 3I/ATLAS observed by STEREO, SOHO, and GOES-19 instruments during September and October 2025. This brightening is reported to scale inversely with the distance from the Sun to the power of -7.5 (±1).
Expert Analysis: Avi Loeb’s Perspective
The discovery has prompted further speculation, including an alternative explanation through ionized carbon monoxide. However, leading astrophysicist and Harvard University director Avi Loeb emphasizes the importance of avoiding premature conclusions about data validity.
In a presentation focused on anomalies in the expansion rate of the Universe, Loeb urged young theorists to consider all possibilities before declaring data invalid. This approach applies equally to the numerous anomalies observed in 3I/ATLAS.
This article provides a detailed overview of recent findings related to the interstellar object 3I/ATLAS and its non-gravitational acceleration, highlighting the implications for understanding both natural celestial phenomena and potential technological signatures.
