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Today, a new paper reported here the most comprehensive analysis of the non-gravitational acceleration of the interstellar object 3I/ATLAS. Its results differ from the official NASA report, posted on the Jet Propulsion Laboratory (JPL) Small Body Database here.
Whereas NASA reports a radial acceleration component away from the Sun that is 5 times larger than the tangential component along the direction of motion of 3I/ATLAS, the new paper derives similar amplitudes for the radial and tangential components. The new analysis suggests that 3I/ATLAS is pushed sideways and not simply away from the Sun — as implied by the official analysis of Davide Farnocchia from NASA/JPL. Yes, official statements from NASA can be wrong. Science is a learning experience.
Does a large non-radial acceleration make sense? Yes, according to high-resolution images of 3I/ATLAS. Observations from August 2026 when 3I/ATLAS was approaching the Sun, reported here the existence of collimated, high-latitude jets that display a periodic wobble consistent with nucleus rotation. This morphology indicated localized sources of mass loss rather than uniform sublimation of the nucleus, which could trigger significant non-radial acceleration. In two papers that I co-authored with Toni Scarmato here and here, we removed the circular glow around the nucleus in the highest-resolution post-perihelion images of 3I/ATLAS from the Hubble Space Telescope, and discovered three symmetrically-separated mini-jets in addition to a prominent sunward jet (anti-tail), modulated by a 7.1 hours rotational period and consistent with a spin-axis orientation within 20 degrees of the sunward direction. Such a configuration naturally favors strongly directional gas and dust emission, capable of generating a transverse acceleration component which is comparable in magnitude to the radial one. It would be interesting to use the geometry of this jet system and demonstrate that the non-gravitational force on the nucleus yields a tangential acceleration comparable in magnitude to the radial one, based on the mass outflow carried by the different jets.
The conclusions of the new paper are based on examining a variety of orbital solutions that implement symmetric, time-offset, and asymmetric radial dependence of the outgassing relative to perihelion. The radial and normal components of the non-gravitational acceleration (labeled, A1 and A3) are broadly consistent across all solutions, whereas the transverse component (A2) is more sensitive to data selection, parameter correlations, and orbital phase coverage. The magnitude of the non-gravitational acceleration can be used to constrain the nucleus diameter of 3I/ATLAS, which most recently was inferred here to be 2.6 kilometers.
The total magnitude of the non-gravitational acceleration is small, about a micrometer (a percent of the width of a human hair) per second squared at the Earth-Sun separation. It corresponds to a spatial offset of 3I/ATLAS by half the radius of the Moon over a period of a month. This offset is smaller than the Earth-Sun separation by a factor of 200,000 and is therefore of negligible significance in shifting the path of 3I/ATLAS relative to the Sun or the planets.
The origin of the symmetric system of 3 mini-jets, separated equally by 120 degrees from each other, remains enigmatic. Does it constitute a technological signature of thrusters? We do not know.
Before my morning jog at sunrise, I received the following uplifting message from the poet Alan Wagstaff in New Zealand.
“Dear Dr Loeb,
You said in a recent essay:
‘This could be done by attending a science-fiction movie, subscribing to belief cults on social-media, using metaverse goggles or taking recreational drugs. These virtual realities bend constraints at will and give rise to a pleasing experience that makes us happy. ‘
Dr.Avi Loeb
