Disappearing induced magnetosphere at Venus: Implications for close-in exoplanets

The solar wind interaction with a planetary atmosphere produces a magnetosphere-like structure near the planet whether or not the planet has an intrinsic global magnetic field. In the case of planets like Venus or Mars, which have no global intrinsic magnetic field but possess a significant atmosphere, a magnetosphere is induced in the highly conducting ionosphere by the time-varying magnetic field carried by the solar wind. The induced magnetosphere at Venus and Mars is almost a permanent feature of the solar wind interaction. Here we report a Venus Express observation of the absence of the dayside part of the induced magnetosphere, when the interplanetary magnetic field (IMF) is nearly aligned with the solar wind flow. Using MHD simulations for this extreme IMF orientation, we examine the global interaction of the solar wind with Venus when the magnetic barrier disappears. Furthermore, we estimate the atmospheric loss under this extreme situation. While this solar wind aligned IMF interaction with a planet case is presently rare, and even rarer over solar system history, it might be an appropriate analogue of the interaction of a stellar wind with close-in exoplanet. Thus the solar wind interaction with Venus under this extreme condition might provide us a natural laboratory for studying the evolution of the atmospheres of hot Jupiters as well as close-in terrestrial planets. Citation: Zhang, T. L., J. Du, Y. J. Ma, H. Lammer, W. Baumjohann, C. Wang, and C. T. Russell (2009), Disappearing induced magnetosphere at Venus: Implications for close-in exoplanets, Geophys. Res. Lett., 36, L20203, doi: 10.1029/2009GL040515.