Magnetic Topology at Venus: New Insights Into the Venus Plasma Environment.

This study provides the first characterization of magnetic topology (i.e., the magnetic connectivity to the collisional ionosphere) at Venus, which might give new insights into the Venusian space environment on topics such as the penetration of the interplanetary magnetic field (IMF) into the ionosphere, planetary ion outflow and inflow, and auroral emission. Magnetic topology is inferred from the electron and magnetic field measurements from Venus Express. We demonstrate through a few case studies that various types of magnetic topologies exist at Venus, including typical draped IMF, open magnetic fields connected to the nightside atmosphere or the dayside ionosphere, and unexpected cross‐terminator closed field lines. We also provide a detailed characterization of an ionospheric hole event, where we find an open topology and a field‐aligned potential of ∼[−10,−20] V with respect to the collisional ionosphere, which has important implications for its formation mechanism. Plain Language Summary: Venus has negligible intrinsic magnetic fields to the first order, such that its ionosphere (the charged part of the atmosphere) interacts directly with the solar wind plasma and magnetic field. Therefore, magnetic connectivity to the ionosphere and/or solar wind is an important piece of information for understanding the near‐Venus space environment and the Sun‐Venus interaction. We utilize measurements from the Venus Express spacecraft to determine magnetic connectivity, or magnetic topology, for the first time. We find three types of magnetic topology at Venus, one of which is unexpected. This study enhances our current understanding of Venus' magnetic configuration and lays the groundwork for a new powerful tool to help understand various topics of the near‐Venus space environment. Key Points: Various types of magnetic topology can be inferred at Venus, including unexpected cross‐terminator closed field linesWe find open magnetic topology and a field‐aligned potential concurring with an ionospheric hole event, hinting at the formation mechanismMagnetic topology can be a new powerful tool to help better understand various topics of the near‐Venus space environment [ABSTRACT FROM AUTHOR]