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Researchers tracked the tail of comet C/2023 P1 (Nishimura) as it interacted with a string of coronal mass ejections, leading to the first-ever quantitative analysis of a cometary tail detachment event.
A photo of comet C/2020 F3 (NEOWISE) showing its narrow bluish ion tail and broader white dust tail. [Juan lacruz; CC BY-SA 4.0]
A Comet’s Journey
When comets journey into the inner solar system, they tend to do so sporting two tails: a dust tail that sweeps back from the comet along its curved trajectory and an ion tail that points away from the Sun, in the direction of the interplanetary magnetic field.
The ion tail, which forms when ultraviolet light from the Sun ionizes gas in a comet’s fuzzy coma, interacts with structures in the solar wind, causing it to shift, sputter, and sometimes even disconnect entirely. Now, for the first time, researchers have quantified the timescales involved when a comet loses — and regrows — its tail.
The Tale of a Tail
Shaheda Begum Shaik (George Mason University; US Naval Research Laboratory) and collaborators studied this phenomenon in observations of the comet C/2023 P1 (Nishimura) from 1 to 14 September 2023. In high-resolution images from the Solar Orbiter Heliospheric Imager, Shaik’s team analyzed the dynamics of C/2023 P1’s tail as the comet braved blustery solar wind conditions in the inner solar system.
In a two-week period, the comet underwent four separate tail disconnection events, in which the connection between the ion tail and the comet was severed. Each of these events coincided with the passage of a coronal mass ejection: a tangled mass of solar plasma and magnetic fields ejected from the Sun’s outer atmosphere.
Solar Orbiter Heliospheric Imager observations of the 11 September 2023 tail disconnection event, which was driven by a passing coronal mass ejection (CME). [Shaik et al. 2026]
Lizard-Like Regrowth
Focusing on the tail disconnection event with the highest-resolution and highest-cadence data, Shaik’s team observed constant small-scale fluttering of the ion tail, reflecting the buffeting of the tail by the solar wind. The tail then developed a kink, which the team speculated is due to compressed solar wind plasma piling up in front of an oncoming coronal mass ejection. The wide-field images show the coronal mass ejection advancing upon the comet and the comet’s tail seemingly being sliced in two.
The free-floating tail segment sped away from the comet at roughly 295 km/s, likely indicating that the tail became caught up in and was transported by the flank of the coronal mass ejection as it barreled past the comet. The timescale and geometry of the event suggest that the interaction of the coronal mass ejection’s magnetic field with the comet’s tail was responsible for the disconnection.
Over the following 24 hours, the comet’s tail slowly regrew at a rate of 86 km/s to its original length of 1.9 million kilometers. The rate of regrowth is likely determined by several factors, such as the rate at which the comet produces ions and the local magnetic field configuration. This work represents a first look at the quantitative behavior of a tail disconnection event, paving the way for future investigations of cometary behavior and a greater understanding of the complex magnetic and plasma environment of the inner solar system.
Citation
“The First Quantitative Study of Cometary Tail Regrowth Following a Coronal Mass Ejection-Driven Disconnection Event,” Shaheda Begum Shaik et al 2026 ApJ 999 60. doi:10.3847/1538-4357/ae3bdb