Prediction at 7.136 hours in the January 2026 TESS flux of 3I/ATLAS depends on aperture and correction

We test whether a reported December brightness period of 7.136 hours predicts the January 2026 TESS aperture flux of comet 3I/ATLAS. We use two unchanged light curves from TSSC release v2.2. We fit a sine with time trends and test prediction between two halves of the longest retained block. Under the planned strict cut, the FFI small-core semiamplitude is 0.433%. Prediction increases weighted squared error by 95.73% in one direction and 27.50% in the reverse direction. The core-plus-tail flux improves prediction in both directions before the extra regression correction. That result fails with a broader sampling cut and after correction. The second product also gives different results. Conditional residual resamples give a small-core coefficient error radius of 0.509% and an amplitude upper value of 0.942%. This value does not limit nucleus variation or include upstream signal loss. We also measure a median sample spacing of 120.001 seconds in the file named fast-lc, which archive text describes as a 20-second product. The evidence shows dependence of the fixed-period test on the released measurement and retained times. It does not establish a rotation period or an instrumental cause. The package preserves inputs, provenance, code, numerical results, and figures.

3I/ATLAS · TESS · interstellar comet · aperture photometry · period prediction · correlated errors · sample spacing · reproducible analysis