Tracking the Activity of the Interstellar Object 3I/ATLAS through its Perihelion
T. Marshall Eubanks, Craig E. DeForest, Kevin J. Walsh, Simon Porter, Thomas Lehmann, Bruce G. Bills, Adam Hibberd, W. Paul Blase, Andreas M. Hein, Robert G. Kennedy, Adrien Coffinet, Pierre Kervella, Carlos Gomez de Olea Ballester
TL;DR
The paper addresses how to track and predict the optical brightness of the interstellar object 3I/ATLAS during perihelion to support interplanetary spacecraft observations. It integrates data from ground-based MPCD/COBS and space-based instruments (PUNCH, LASCO/C3, GOES-19 CCOR-1) to model coma brightness drift using an empirical magnitude equation $m = H_{1} + 5\log_{10}(D_{observer}) + K_{1}\log_{10}(R_{Sun})$. The authors implement and update a gas-dominated model with $m = H_{1} + 5\log_{10}(D_{observer}) + K_{1}\log_{10}(R_{Sun})$ and, after October data, introduce an asymmetric post-perihelion drift with $K_{2}$ and $H_{2}$ (e.g., $K_{2} = 14.54$, $H_{2} = 5.48$), while dust parameters are kept fixed. The results demonstrate continuous coverage through perihelion and suggest no dramatic nucleus disruption, with ongoing monitoring planned toward the 2026 Jupiter approach.
Abstract
In order to facilitate interplanetary spacecraft observationsof 3I/ATLAS, we have monitored and predicted the optical properties of its coma using both ground and space-based observations. Here, we describe how the data from space-based solar coronagraphs and the PUNCH mission enabled tracking of 3I/ATLAS's optical magnitude throughout its entire perihelion passage, including the period between October 8 and 30, 2025, when it was not visible from Earth.