The First Quantitative Study of Tail Regrowth of CME-Driven Disconnection in Comet C/2023 P1 Nishimura

TL;DR

The paper addresses how cometary ion tails respond to transient solar wind structures by presenting the first quantitative study of tail regrowth following CME-driven disconnections in C/2023 P1 Nishimura using SoloHI imagery. It combines 3D CME reconstruction with high-cadence inner-heliospheric imaging to show that tail disconnections occur when the CME flank encounters the comet, followed by a gradual tail reformation with a measured rate of $86\pm7$ km s$^{-1}$ over about 24 hours. The detached tail drifts anti-sunward at $295\pm20$ km s$^{-1}$, consistent with transport by the CME flank, underscoring a flank-driven, magnetically mediated interaction. This work provides a direct, quantitative benchmark for tail regrowth and demonstrates SoloHI's capability to resolve fine-scale plasma-tail dynamics in the inner heliosphere, enriching our understanding of comet–solar wind–CME interactions and magnetic draping effects.

Abstract

Comet C/2023 P1 (Nishimura) was observed by the Solar Orbiter Heliospheric Imager (SoloHI), onboard the Solar Orbiter spacecraft, from 2023 September 1 to 14. During this period, the ion tail of the comet exhibited continual fluctuations and four tail disconnection events (TDEs), each coinciding with the passage of a coronal mass ejection (CME). In this work, we report on the ion tail dynamics of the best observed TDE, which occurred on September 11. The SoloHI white-light images reveal an abrupt bending, subsequent kinks, and severing of a downstream portion of the pre-existing ion tail. The onset of disconnection occurred $\sim$6.5 hours after the projected passage of the CME leading edge in the images, consistent with a CME flank encounter. After the disconnection, the ion tail reformed within $\sim$24 hours, with a regrowth rate of $\sim$86$\pm7~\mathrm{km\,s^{-1}}$, indicating the rate at which newly ionized material forms along the magnetic field draped around the comet's coma. After the TDE, the detached tail drifted anti-sunward at an estimated speed of $\sim$295$\pm20~\mathrm{km\,s^{-1}}$, comparable to the local CME flank's speed, suggesting that the severed plasma was most likely carried away from the comet by the CME. This study provides the first direct, quantitative characterization of comet-CME interactions and the subsequent regrowth phase of a cometary TDE. These measurements were achievable by SoloHI's unique inner-heliospheric coverage, thanks to a combination of high photometric sensitivity, short exposure times, and a wide field of view that preserves the fine-scale tail dynamics.

Figures (4)

• Figure 1: Trajectory of C/2023 P1 comet, with the respective positions of Solar Orbiter, the nearby planets, and other spacecraft. (a) Side view of the comet location relative to the ecliptic plane on 2023 September 11. The blue dashed arrow indicates the direction of the comet trajectory. The path of the comet above the ecliptic plane is shown in solid blue, and below in dashed blue. An inset shows the SoloHI FOV (gray shaded region enclosed by the red outline) on that day. (b) The ecliptic plane and the comet's path as viewed from above the solar north pole. The green-shaded region shows the extent of the CME associated with the TDE under study and illustrates the geometry of CME-comet interaction. The polar map in the background layer is produced using the Solar-MACH gieseler_solar-mach_2023. (c) Comet-Sun-Solar Orbiter geometry, the comet and Orbiter trajectory during the analysis period of 2023 September 11, 00:00 UT to 12, 23:59 UT. The orbital ephemerides are obtained from the JPL Horizons page. This schematic renders the simplified CME-comet geometry and is not drawn to scale.
• Figure 2: SoloHI observations of the C/2023 P1 comet-CME interaction on 2023 September 11. (a) Snapshot of the full SoloHI mosaic FOV, where the Sun is to the right of the image. The grid, delineated by continuous lines, depicts the longitude and latitude in the HPC coordinate system, and the dashed line indicates the ecliptic plane. (b--g) Time sequence of selected image frames of the subfield marked in a red box of panel (a) showcasing the comet-CME interaction. The orange arrows highlight the kink in the tail, and the yellow arrow indicates the detached tail. After disconnection, tail regrowth is shown in the last two snapshots of the sequence, as indicated by the tail length and intensity, highlighted by the blue dashed arrows. A movie illustrating the overall evolution of the comet, its interactions with CMEs and TDEs, is available in the online version of the article. The movie first presents the wide-field evolution in the mosaic view of tiles 3 and 2, followed by a zoomed-in view of the selected subfield.
• Figure 3: Time sequence of selected SoloHI image frames illustrating the tail dynamics and disconnection event in a zoomed view of the comet in the subfield. The orange circles mark the intensity across the tail at a few selected regions along the tail, whereas the magenta circles indicate those for the disconnected tail. The white arrow in panel (a) indicates the sunward direction, toward the right side of the subfield.
• Figure 4: Rate of regrowth of the ion tail after the disconnection event. The inset figure shows the comet and the CME as they propagate in the SoloHI tile 2 FOV. Abrupt decrease in tail length near 19:00 UT on 2023 September 11 indicates the tail disconnection, following the CME crossing and flank encounter (red arrows on the top). The extent of the comet's tail entering the FOV is shown in blue symbols in the plot. The tail remains fully within the FOV for four consecutive frames (marked by the purple arrow), after which the disconnection and regrowth are observed. The purple overbar marks the CME’s passage duration through the SoloHI FOV, CME's entry (light purple), the leading edge passage in projection before the comet-CME interaction (medium), and the interval after the comet crosses the CME flank (dark). The growth rate is determined from the slope of the linear fit indicated by the green line.