Resolve the indeterminate pre-perihelion lightcurve of 3I/ATLAS beyond 5.6 au

Determine the heliocentric brightness variation and corresponding heliocentric index n of interstellar comet 3I/ATLAS at heliocentric distances r_H ≥ 5.6 au, where existing photometric datasets from ATLAS, ZTF, and TESS are mutually inconsistent and the lightcurve behavior has been deemed indeterminate.

Background

The authors combine pre-perihelion photometry from multiple facilities (NOT, ATLAS, ZTF, TESS) to fit the heliocentric lightcurve of 3I/ATLAS. While the heliocentric index n ≈ 3.8 is well constrained for r_H ≲ 5 au, the datasets diverge at larger heliocentric distances.

Specifically, ATLAS, ZTF, and TESS measurements do not agree for r_H ≥ 5.6 au, leading the authors to judge that segment of the lightcurve as indeterminate. Clarifying the brightness evolution in this range would establish how activity developed at earlier distances and improve constraints on volatile-driven dust production.