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Post-perihelion brightness evolution of 3I/ATLAS

Determine the post-perihelion optical brightness evolution of interstellar comet 3I/ATLAS, specifically whether it will plateau, briefly continue brightening, or undergo rapid fading after perihelion.

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Background

Although the comet is expected to be observable again after perihelion, the lack of a physical explanation for its pre-perihelion behavior leaves its post-perihelion trend uncertain.

Clarifying the post-perihelion evolution is important for planning and interpreting follow-up observations and for understanding the activity of interstellar comets.

References

Without an established physical explanation, the outlook for 3I's post-perihelion behavior remains uncertain, and a plateau in brightness---or even a brief continuation of its pre-perihelion brightening---appears as plausible as rapid fading past perihelion.

— Rapid Brightening of 3I/ATLAS Ahead of Perihelion (2510.25035 - Zhang et al., 28 Oct 2025) in Section 4 (Discussion)