The structure of Venus’ middle atmosphere and ionosphere

Still delivering ESA's Venus Express probe has been in orbit since April 2006. Eight research papers in this issue present new results from the mission, covering the atmosphere, polar features, interactions with the solar wind and the controversial matter of venusian lightning. Håkan Svedham et al . open the section with a review of the similarities and (mostly) differences between Venus and its 'twin', the Earth. Andrew Ingersoll considers the latest results, and also how the project teams plan to make the most of the probe's remaining six years of life. Radio-sounding results from the first Venus Express Radio Science (VeRa) occultation season are reported, which determine the fine structure in temperatures at upper cloud-deck altitudes, detect a distinct day–night temperature difference in the southern middle atmosphere, and track day-to-day changes in Venus' ionosphere. The atmosphere and ionosphere of Venus have been studied in the past by spacecraft with remote sensing 1 , 2 , 3 , 4 or in situ techniques 3 , 4 . These early missions, however, have left us with questions about, for example, the atmospheric structure in the transition region from the upper troposphere to the lower mesosphere (50–90 km) and the remarkably variable structure of the ionosphere. Observations become increasingly difficult within and below the global cloud deck (