Review of recent observations of magnetic holes in the solar wind

Magnetic holes (MHs) are ubiquitous coherent structures within the solar wind, defined by localized depressions in the magnetic field. They are increasingly recognized as fundamental sites of energy conversion and particle energization, playing a crucial role in the dynamic evolution of solar wind. This review summarizes recent observational advances in the study of solar wind MHs. We first outline their statistical properties, general distribution and evolution, followed by a discussion of competing formation scenarios, contrasting classical instability-driven models with those invoking turbulence, magnetic reconnection, or the self-consistent emergence of coherent structures. We then examine observational signatures of energy conversion within MHs, including plasma heating and associated wave activity. Beyond their local properties, MHs are also dynamic solar wind structures that interact with various plasma environments. We further discuss how they traverse the heliosphere, cross planetary bow shocks, and evolve under the different plasma environments of planets and comets. By synthesizing these findings, we highlight the multifaceted nature of MHs and emphasize how recent instrumental advances have deepened our understanding. A complete physical understanding of their role in solar wind dynamics now demands a synergy between coordinated multi-spacecraft missions, capable of tracing these structures through the heliosphere, and the continued development of advanced theoretical and simulation frameworks.