Comet dust tails as a tracer for the solar wind.

The sublimation of volatiles from comets near the Sun such as water ice results in the ejection of vast quantities of dust grains from the nucleus. These ejected grains are then sorted by radiation pressure forces to form a dust tail. Visually spectacular dust tails, such as that of C/2006 P1 (McNaught), often display linear striations across the tail, termed striae, the formation of which remains debated, with suggestions that they result either from fragmentation [1] or from solar-wind-related mechanisms [2, 3].

Comet C/2024 G3 (ATLAS) is another example of a visually spectacular comet with well-defined striae. In January 2025, the comet’s dust tail passed through the fields of view of the wide field cameras onboard the Solar Terrestrial Relations Observatory, Solar Orbiter, and Solar and Heliospheric Observatory missions. Here we present an analysis of these images using a method known as temporal mapping [2], which transforms an image of a dust tail into a fixed phase space in which the date of grain ejection is represented on the x-axis and the ratio of radiation pressure to gravitational force (grain β) is represented on the y-axis. The technique identifies numerous striae across the tail, and we discuss the effects of solar-wind structures such as the heliospheric current sheet, which separates regions of opposite magnetic polarity, and the surrounding heliospheric plasma sheet. The temporal mapping technique can help improve our understanding of the nature of cometary dust-grain interactions with the solar wind and reveal otherwise invisible solar-wind structures.

[1] Sekanina, Z. and Farrell, J. A.: The striated dust tail of Comet West 1976 VI as a particle fragmentation phenomenon, The Astronomical Journal, 85, 1538–1554, 1980. doi:10.1086/112831.

[2] Oliver Price, Geraint H. Jones, Jeff Morrill, Mathew Owens, Karl Battams, Huw Morgan, Miloslav Drückmüller and Sebastian Deiries: Fine-scale structure in cometary dust tails I: Analysis of striae in Comet C/2006 P1 (McNaught) through temporal mapping, Icarus, 319, 540–557, 2019. doi:10.1016/j.icarus.2018.09.013.

[3] Oliver Price, Geraint H. Jones, Karl Battams and Mathew Owens: Fine-scale structure in cometary dust tails II: Further evidence for a solar wind influence on cometary dust dynamics from the analysis of striae in comet C/2011 L4 Pan-STARRS, Icarus, 389, 115218, 2023. doi:10.1016/j.icarus.2022.115218.