Abstract. In situ measurements of the magnetic field are vital to the study of many fundamental problems in planetary research. Therefore the magnetometer experiment is a key element of the payload of Venus Express. In addition to the interaction of the solar wind with Venus, these measurements are crucial for the study of atmospheric escape and detection of lightning. However, the methodology for the magnetic field measurements had to be different to the traditional approach, because Venus Express is not a magnetically clean spacecraft. A technique based on two-point simultaneous measurements of the magnetic field and systems identification software is used to separate the natural magnetic field from the spacecraft generated interference. In this paper an overview of the techniques developed to separate these two field types and the results achieved for 1 Hz Venus Express data are presented. Previous publications suggest that the resulting Venus Express cleaned data is of comparable quality to measurements made from onboard magnetically clean spacecraft (Zhang et al., 2008a, b; Slavin et al., 2009). Therefore the magnetometer experiment is a key element of the payload of Venus Express. In addition to the interaction of the solar wind with Venus, these measurements are crucial for the study of atmospheric escape and detection of lightning. However, the methodology for the magnetic field measurements had to be different to the traditional ap- proach, because Venus Express is not a magnetically clean spacecraft. A technique based on two-point simultaneous measurements of the magnetic field and systems identifica- tion software is used to separate the natural magnetic field from the spacecraft generated interference. Magnetospheric physics (Solar wind interac- tions with unmagnetized bodies) – General or miscellaneous (Instruments useful in three or more fields; Techniques ap- plicable in three or more fields) 1 Introduction The scientific payload of Venus Express (VEX) includes MAG, which is an experiment to make in situ measurements of the local magnetic field vector. These measurements are Correspondence to: T. L. Zhang (tlzhang@ustc.edu.cn) crucial to studying the interaction of the solar wind with Venus (Zhang et al., 2007). However, the VEX spacecraft bus is a twin to that of Mars Express, which was not de- signed to be magnetically clean or to carry a magnetometer. As a result no action is required to compensate for the effect from the APSERA instrument in the 1 Hz data. 4.5 Reaction wheel interference Reaction wheels are well known as a cause of interference in the magnetic field measurements made by spacecraft (e.g. Narvaez, 2004; Glassmeier et al., 2007). The angular ve- locities of the reaction wheels on Venus Express change in discrete intervals several times over the course of each 24 h orbit. Their operation leads to an oscillatory signal with ap- proximately zero mean and a frequency which is observed to vary slowly in the high sample rate data. The result is a data set that is estimated to have a dynamic field accuracy of much bet- ter than 0.1 nT and is comparable to the measurements made from onboard a magnetically clean spacecraft (Zhang et al., 2008a, b). The statement that the data is of comparable qual- ity to measurements made from onboard magnetically clean spacecraft, is also supported by the comparison of magnetic field The loss of matter from the atmosphere and its affect on the evolution of the atmosphere of Venus is one of the im- portant questions high-lighted for Venus Express. Zhang et al. (2007) suggest that the curved magnetic field configura- tion in the night-side ionosphere and tail close to the planet could lead to acceleration of plasma, resulting in some atmo- spheric loss. Pope et al. (2009) have detected what appear to be large wave like structures on the boundary between the ionosphere and magnetic barrier. These waves develop into structures which indicate a vortex configuration, which has previously been linked to the loss of atmospheric plasma (Wolff et al., 1980). These structures could also aid in the redistribution of ionospheric plasma created in the day-side through to the night-side during the long (58 terrestrial day) nights. Delva et al. (2008) studied proton cyclotron waves in the solar wind upstream of Venus. The occurrence of these waves near Venus suggests neutral planetary hydrogen atoms extend away from Venus. These atoms are ionised through various processes, picked-up by the solar wind in the form of protons and transported away from the planet. Zhang et al. (2008b) used VEX MAG data to study the lo- cation and structure of the magnetic barrier at Venus. The resulting cleaned datasets are of comparable quality to magnetic field measurements made onboard mag- netically clean spacecraft. These cleaned data sets have been instrumental in studies which have discovered new plasma interactions while investigating the local plasma environment Ann. Geophys., 29, 639–647, 2011 www.ann-geophys.net/29/639/2011/ S. A. Pope et al.: Exploring planetary magnetic environments 647 near Venus at solar minimum for the first time. These discov- eries endorse the new magnetic field measurement approach which has been used for the first time with Venus Express. Acknowledgements. Rev., 114, 385–394, doi:10.1007/s11214- 004-1433-1, 2004. Ness, N. F., Behannon, K. W., Lepping, R. P., and Schatten, K. H.: Use of Two Magnetometers for Magnetic Field Measurements on a Spacecraft, J. Geophys. Res., 76, 3564–3573, 1971. Ness, N. F., Behannon, K. W., Lepping, R. P., Whang, Y . C., and Schatten, K. H.: Magnetic field observations near Venus: Prelim- inary results from Mariner 10, Science, 183, 1301–1306, 1974. Pope, S. A., Balikhin, M. A., Zhang, T. L., Fedorov, A. O., Gedalin, M., and Barabash, S.: Giant V ortices lead to Ion Escape from Venus and re-distribution of plasma in the Ionosphere, Geophys. Res. Lett., 36, L07202, doi:10.1029/2008GL036977, 2009. Slavin, J.

<p class="Sectiontext"><span lang="EN-US">Venus appears to be an “alien” planet drastically and surprisingly different from the Earth. The early space missions revealed the world with remarkably hot, dense, cloudy, and very dynamic atmosphere filled with toxic species likely of volcanic origin. During more than 8 years of operations ESA’s Venus Express spacecraft performed a global survey of the atmosphere and plasma environment of our near neighbour. The mission delivered comprehensive data on the temperature structure, the atmospheric composition, the cloud morphology, the atmospheric dynamics, the solar wind interaction and the escape processes. Vertical profiles of the atmospheric temperature showed strong latitudinal trend in the mesosphere and upper troposphere correlated with the changes in the cloud top structure and suggesting convective instability in the main cloud deck at 50-60 km. Observations revealed significant latitudinal variations and temporal changes in the global cloud top morphology, which modulate the solar energy deposited in the atmosphere. The cloud top altitude varies from ~72 km in the low and middle latitudes to ~64 km in the polar region, correlated with decrease of the aerosol scale height from 4 ± 1.6 km to 1.7 ± 2.4 km, marking vast polar depression. UV imaging showed for the first time the middle latitudes and polar regions in unprecedented detail. In particular, CO Meeting Organizer EPSC2022 Home Blueprint page 1){window.history.go(-1);}return false;">[Back] [Session TP2] EPSC Abstracts Vol. 16, EPSC2022-1120, 2022 https://doi.org/10.5194/epsc2022-1120 Europlanet Science Congress 2022 © Author(s) 2022. This work is distributed under the Creative Commons Attribution 4.0 License. Venus Express as precursor of the Venus Decade Dmitrij Titov 1,2 , Anne Grete Straume-Lindner 2 , and Colin Wilson 2 Dmitrij Titov et al. Dmitrij Titov 1,2 , Anne Grete Straume-Lindner 2 , and Colin Wilson 2 1 University of Leiden, The Netherlands (dmitri.titov58@gmail.com) 2 ESA / ESTEC, SSO, Noordwijk, The Netherlands 1 University of Leiden, The During more than 8 years of operations ESA’s Venus Express spacecraft performed a global survey of the atmosphere and plasma environment of our near neighbour. The mission delivered comprehensive data on the temperature structure, the atmospheric composition, the cloud morphology, the atmospheric dynamics, the solar wind interaction and the escape processes. Vertical profiles of the atmospheric temperature showed strong latitudinal trend in the mesosphere and upper troposphere correlated with the changes in the cloud top structure and suggesting convective instability in the main cloud deck at 50-60 km. Solar occultation observations and deep atmosphere spectroscopy in spectral transparency “windows” mapped distribution of the major trace gases H 2 O, SO 2 , CO, COS and their variations above and below the clouds, revealing key features of the dynamical and chemical processes at work. A strong, an order of magnitude, increase in SO 2 cloud top abundance with subsequent return to the previous concentration was monitored by Venus Express specrometres. This phenomenon can be explained either by a mighty volcanic eruption or atmospheric dynamics. Tracking of cloud features provided the most complete characterization of the mean atmospheric circulation as well as its variability. A reverse equatorward flow was found about 20 km deeper in the middle cloud suggesting existence of a Hadley cell or action of thermal tides at the cloud level. Comparison of the thermal wind field derived from temperature sounding to the cloud-tracked winds confirms the validity of cyclostrophic balance, at least in the latitude range from 30S to 70S. The observations are supported by the General Circulation Models. Venus Express detected and mapped non-LTE infrared emissions in the lines of O 2 , NO, CO 2 , OH originating near the mesopause at 95-105 km. The data show that the peak intensity occurs in average close to the anti-solar point for O 2 emission, which is consistent with current models of the thermospheric circulation. For almost complete solar cycle the Venus Express instruments continuously monitored the induced magnetic field and plasma environment and established the global escape rates of 3·10 24 s −1 , 7·10 24 s −1 , 8·10 22 s −1 for O + , H + , and He + ions and identified the main acceleration process. For the first time it was shown that the reconnection process takes place in the tail of a non-magnetized body. It was confirmed that the lightning tentatively detected by Pioneer-Venus Orbiter indeed occurs on Venus. Thermal mapping of the surface in the near-IR spectral “windows” on the night side indicated the presence of recent volcanism on the planet, as does the high and strongly variable SO 2 abundance. Variations in the thermal emissivity of the surface observed by the VIRTIS imaging spectrometer indicated compositional differences in lava flows at three hotspots. These anomalies were interpreted as a lack of surface weathering suggesting the flows to be younger than 2.5 million years indicating that Venus is actively resurfacing. Furthermore, Venus can be considered as an archetype of terrestrial exoplanets that emphasizes an important link to the quickly growing field of exoplanets research. The talk will give an overview of the Venus Express findings including recent results of data analysis, outline outstanding unsolved problems and provide a bridge, via the Akatsuki mission, to the missions to come in 2030s: EnVision, VERITAS and DAVINCI. How to cite: Titov, D., Straume-Lindner, A. G., and Wilson, C.: Venus Express as precursor of the Venus Decade, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1120, https://doi.org/10.5194/epsc2022-1120, 2022.