Interactions between solar wind and comets

Comets are a class of small, irregularly shaped objects in a solar system consisting mainly of volatile materials. During the approach of a comet to the sun, the neutral component of the volatile matter released by heating in the nucleus becomes charged after a process of photoionization, charge exchange, and electron impact, forming a ray-like plasma comet tail. This charged component results in pick-up ions, which are mostly water group ions (H₂O⁺, O⁺) that are heavier than H⁺. Therefore, the conservation of momentum causes the solar wind to slow down during the pick-up or mass loading. As a result, the interplanetary magnetic field carried by the solar wind plasma accumulates around the comet nucleus. Simultaneously, owing to the angle between the direction of the solar wind velocity and direction of the interplanetary magnetic field, the velocity distribution of the pick-up ions has a ring-like distribution, providing free energy for wave excitation; thus, contributing to the development of turbulence. The neutral cometary component and solar wind plasma also radiate X-rays and extreme ultraviolet radiation during charge exchange, providing the possibility to determine the composition and state of the solar wind using spectral intensity analysis. The study of cometary activity and its interaction with solar wind is essential for understanding the composition and structural dynamics of cometary materials, evolution of solar wind in the heliosphere, and origin of organic matter and life in the solar system. In this study, we reviewed the research progress on solar wind-comet interactions from three perspectives: in situ detection, remote sensing observation, and theoretical simulation, and provided some prospects for future research trends.