Abstract This paper presents a pre-registered harmonic prediction for the interstellar object 3I/ATLAS associated with its close approach to Jupiter on March 16, 2026. Observations to date indicate a transition in the object’s rotational or wobble period from approximately 7.75 hours prior to perihelion to approximately 7.14 hours post-perihelion, along with a persistent three-jet morphology separated by roughly 120 degrees. Using the ratio implied by the observed period shift, a subsequent stable harmonic state near 6.58 hours is predicted. In addition to this ratio-derived harmonic, a secondary geometry-locked resonance near 5.9–6.0 hours is identified as a distinct possibility if the object transitions to a maximum stable rotational frequency compatible with its observed jet configuration. The timing of this potential transition is predicted to coincide with the object’s traversal of Jupiter’s Hill sphere boundary, approximately 53.4 million kilometers from the planet, rather than occurring gradually with heliocentric distance. This framework predicts a shortening of the rotation period during the Jupiter encounter window, contrary to standard expectations of rotational stasis or spin-down as outgassing declines. Explicit, time-bounded criteria for confirmation or falsification are provided. If no rotation-state transition is observed within the defined window, the proposed harmonic framework is disfavored.
Michael James Gross (Sat,) studied this question.