THE UPPER ATMOSPHERE OF VENUS OBSERVED BY VENUS EXPRESS

The upper atmosphere of Venus is still nowadays a highly unknown region in the scientific context of the terrestrial planetary atmospheres. The Earth’s stratosphere and mesosphere continue being studied with increasingly sophisticated sounders and in-situ instrumentation [1, 2]. Also on Mars, its intensive on-going exploration is gathering a whole new set of data on its upper atmosphere [3, 4, 5]. On Venus, however, the only recent progress came from theoretical model developments, from ground observations and from revisits of past missions’ data, like Pioneer Venus. More and new data are needed [6, 7, 8]. The arrival of the European Venus Express (VEX) mission at Venus on April 2006 marked the start of an exciting period with new data from a systematic sounding of the Venus atmosphere from orbit [9, 10]. A suite of diverse instrumentation is obtaining new observations of the atmosphere of Venus. After one and a half years in orbit, and although the data are still under validation and extensive analysis, first results are starting to be published. In addition to those global descriptions of VEX and its first achievements, we present here a review on what VEX data are adding to the exploration of this upper region of the atmosphere of Venus. We present measurements at those altitudes from one of the infrared sounders aboard VEX, the instrument VIRTIS, as an example of unique insights on the upper mesosphere and lower thermosphere of Venus, and discuss briefly the synergy with other instruments on VEX. We will conclude with our opinion on the importance and limitations of the Venus Express mission in order to broaden our global understanding of the upper layers of the terrestrial atmospheres.