3I/ATLAS

We analyse data on the post-perihleion morphology, including jet position angles (PAs) and coma dominated photometry of the interstellar object 3I/ATLAS. From Hubble Space Telescope (HST) im ages processed with a Larson–Sekanina rotational-gradient filter, we measure the PAs of three main persistent jet-like features between November 30 and December 27, 2025 and fit a weighted Fourier model in a period scan. The dominant jet PA wobble yields Pjet = 7.20±0.05 h. An independent Gr (≈ R) time-series photometry data set, using two different apertures from MPC station L92, analyzed with nightly offsets and 30-minute binning, gives Pphot = 7.136 ± 0.001 h (formal 1σ), with a semi amplitude A ≃ 0.311 mag and scatter σjit ≃ 0.089 mag. The close agreement beetwen the periods supports a characteristic post-perihelion period of ∼ 7.1 h. We interpret this period as an attitude precession/nutation (non-principal-axis rotation) traced by jet orientation and coma flux redistribu tion. The jet structure precesses about the rotation axis with a characteristic angular excursion of order ∼ 20◦, and the rotation axis is aligned with the sunward direction to within ∼ 20◦