Formation, Detection, and Characterization of Extrasolar Habitable Planets Proceedings IAU Symposium No. 293, 2012 N. Haghighipour, ed. c  International Astronomical Union 2014 doi:10.1017/S1743921313013100 Variations and Effects of the Venusian Bow Shock from VEX Mission Yansong Xue and Shuanggen Jin Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China. email: xys@shao.ac.cn; sg.jin@yahoo.com Abstract. The upper atmosphere of Venus is not shielded by planetary magnetic field from direct interaction with the solar wind. The interaction of shocked solar wind and the ionosphere results in ionopause. Magnetic barrier, the inner region of dayside magnetosheath with the dominated magnetic pressure deflects the solar wind instead of the ionopause at solar maximum. Therefore, the structure and interaction of venusian ionosphere is very complex. Although the Venus Express (VEX) arrived at Venus in April 2006 provides more knowledge on the Venusian ionosphere and plasma environment, compared to Pioneer Venus Orbiter (PVO) with about 14 years of observations, some important details are still unknown (e.g., long Venusian bow shock variations and effects). In this paper, the bow shock positions of Venus are determined and analyzed from magnetometer (MAG) and ASPERA-4 of the Venus Express mission from May 28, 2006 to August 17, 2010. Results show that the altitude of BS was mainly affected by SZA (solar zenith angle) and Venus bow shocks inbound and outbound are asymmetry. Keywords. Venus, Bow shock, Magnetic field, Venus Express 1. Introduction Venus has a dense atmosphere without intrinsic magnetic field, so the solar wind inter- acts directly with its upper atmosphere. A Bow shock is caused by the deflection of the oncoming supersonic solar wind around the planet in the highly conductive ionosphere. The interaction of post-shock solar wind flow and the ionosphere results in a distinct boundary, which is called ionopause. This ionopause separates the thermal plasma of the ionosphere from the hot magnetized plasma of the magnetosheath. The Pioneer Venus Orbiter (PVO) mission (from 1978 to 1992) provided a data set to research the solar wind interaction with Venus over a complete solar cycle (Russell et al. 2006). The bow shock of Venus is originally identified using data from the PVO magnetome- ter and plasma analyzer. In comparison with the magnetometer (MAG) and the plasma analyzer (ASPERA-4) on board of Venus Express (VEX) spacecraft, however, the reso- lution of the PVO instruments is lower. Using VEX, the location of Venus bow shock can be accurately retrieved, which also fill the gaps in the PVO observations and extend our knowledge of the plasma environment of Venus. Based on nearly 2000 PVO shock cross- ings, Russell et al. 1988) and Zhang et al. 1990) examined the Venus bow shock and found that the Venus bow shock location was influenced by the solar cycle and solar EUV flux, the upstream solar wind parameters and the orientation of the interplanetary magnetic field (IMF) (Phillips & McComas. 1991, Russell et al. 2006). Furthermore, a simple conic section was used to model the bow shock focusing the center of the planet based on PVO data. In this study we determined the locations of the Venus bow shock using magnetic and particle measurements obtained by magnetometer (MAG) and electron spectrometer (ELS), and the variations of Venus bow shock are analyzed with a long observations. 329 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921313013100 Downloaded from https://www.cambridge.org/core. IP address: 3.236.55.199, on 16 Jun 2020 at 05:55:13, subject to the Cambridge Core terms of use, available at