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Prospects for the Crossing of Comet 3I/ATLAS's Ion Tail

Samuel R. Grant, Geraint H. Jones

Abstract

During October - November 2025, interstellar comet 3I/ATLAS, will pass upstream of the Europa Clipper and Hera spacecraft. Here, we identify two potential opportunities for in-situ observations of 3I's ion tail by immersion, facilitated by the close alignment between the comet's hyperbolic trajectory with the ecliptic plane. During the period 30 October - 6 November 2025, it is predicted that Europa Clipper will potentially be immersed within the ion tail of 3I/ATLAS, providing the opportunity to detect the signatures of an interstellar comet's ion tail. Characteristic changes to the solar wind are also expected to be observed; a magnetic draping structure associated with the comet may be identifiable. It is further predicted that spacecraft Hera will possibly be immersed within the ion tail of 3I/ATLAS during the period 25 October - 1 November 2025.

Prospects for the Crossing of Comet 3I/ATLAS's Ion Tail

Abstract

During October - November 2025, interstellar comet 3I/ATLAS, will pass upstream of the Europa Clipper and Hera spacecraft. Here, we identify two potential opportunities for in-situ observations of 3I's ion tail by immersion, facilitated by the close alignment between the comet's hyperbolic trajectory with the ecliptic plane. During the period 30 October - 6 November 2025, it is predicted that Europa Clipper will potentially be immersed within the ion tail of 3I/ATLAS, providing the opportunity to detect the signatures of an interstellar comet's ion tail. Characteristic changes to the solar wind are also expected to be observed; a magnetic draping structure associated with the comet may be identifiable. It is further predicted that spacecraft Hera will possibly be immersed within the ion tail of 3I/ATLAS during the period 25 October - 1 November 2025.
Paper Structure (2 sections, 1 figure)

This paper contains 2 sections, 1 figure.

Table of Contents

  1. Section

Figures (1)

  • Figure 1: (Upper) Impact parameters for Europa Clipper relative to comet 3I/ATLAS for purely radial SW velocities 200, 450 and 900 km/s. The minima for the three curves fall between 30 October and 6 November 2025. (Lower) Simulation of 3I/ATLAS's ion tail on 1 November 2025 assuming a 460 kms$^{-1}$ radial flow. Positions of Europa Clipper, Sun, Hera, and 3I/ATLAS are shown in a frame where the Sun-Europa Clipper line is fixed. The plane represents that of the ecliptic, with grid lines spaced at 0.1 au. The comet's position is shown every 6 hours, with legs showing its position north of the ecliptic. Europa Clipper is also north of the ecliptic by 0.069 au. Earth and Mars's mean orbital distances are included for scale.