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Harvard astrophysicist Avi Loeb has revealed that 3I/ATLAS, the interstellar object that passed closest to the Sun on its perihelion journey, displayed the first confirmed evidence of non-gravitational acceleration during its solar approach.

NASA engineer Davide Farnocchia from the Jet Propulsion Laboratory documented the anomaly at a distance of 203 million kilometers from the Sun, measuring two distinct acceleration components: a radial push away from the Sun at 135 kilometers per day squared and a transverse acceleration of 60 kilometers per day squared relative to the Sun's direction.

The object's trajectory shifted during the period when it endured intense solar blasts while positioned behind the Sun, raising fundamental questions about whether this behavior stems from natural outgassing or represents something far more unusual.

Scientists now face two competing explanations for the acceleration. If conventional comet-like outgassing drives the movement, momentum conservation calculations suggest 3I/ATLAS would lose approximately ten percent of its total mass during its month-long transit through the perihelion region, with a complete half-life of just six months at current ejection rates. Such dramatic mass loss should produce an enormous detectable gas plume surrounding the object throughout November and December 2025.

The European Space Agency's Juice spacecraft is positioned to observe any such plume during the first week of November, while hundreds of ground-based telescopes plus the Hubble and Webb space telescopes will train their instruments on 3I/ATLAS when it makes its closest approach to Earth on December 19, 2025, at a distance of 269 million kilometers.

The acceleration measurements align with troubling observations from September and October 2025 captured by STEREO, SOHO and GOES-19 instruments, which recorded an unusual rapid brightening of the object.

The brightness increased inversely with distance from the Sun to the power of negative 7.5, a relationship that defies typical comet behavior and suggests either massive volatile evaporation or an alternative mechanism entirely. Adding to the mystery, recent reports indicate 3I/ATLAS appeared bluer than the Sun during perihelion, representing the ninth documented anomaly in the object's already peculiar profile.

Natural comets typically display reddened light from dust scattering, and with surface temperatures expected to reach only one-twentieth of the Sun's 5,800 degrees Kelvin photosphere, the blue coloration challenges conventional explanations.