 The Venus Express Mission Håkan Svedhem Project Scientist ESAC, Spain 27 April 2010

 Venus Express Why Venus? –We have been there before –What do we know? –What do we still not know?

 Venus is just yellow-white to the naked eye. In ultraviolet light however much structure can be seen as shown in this pre VEX image. This is caused by a still unknown substance absorbing part of the light and being modulated by the high winds in the upper cloud layer.

 In 1984 David Allen, by chance, discovered that there is a lot of structure in near infrared light on the dark side of the planet. This is thermal radiation from the hot lower atmosphere, and even from the surface, as shown in this 1.7 micrometer image from the Galileo spacecraft.

 Two of the very few existing images from the surface of Venus, from the Venera landers

 Plasma and escape processes Brace & Kliore (1980)

 Science Objectives The aim of the mission is to carry out a comprehensive study of the atmosphere of Venus and to study to some detail the plasma environment and number of aspects of the surface of the planet. Full exploitation of the infrared spectral windows

 Science Themes –Atmospheric Dynamics Global Dynamics mechanisms, Super-rotation, Double Polar Vortex –Atmospheric Structure Density and Temperature in three dimensions –Atmospheric Composition and Chemistry Processes and species in the different regions –Cloud Layer and Hazes Behaviour and characteristics, UV absorber –Radiative Balance and Greenhouse effect Global thermal balance, Greenhouse in past, present and future –Surface Properties and Geology Volcanic and seismic activity, highly radar reflective areas –Plasma Environment and Escape processes Evolution of the atmosphere, water, escape history

 Over All Objective Comparative planetology: –Why has Venus evolved in such a dramatically different way compared to the Earth and Mars in spite of the many similarities in their original physical and chemical properties and what parameters control the evolution of planets and their atmospheres in general? –If we can understand how the climate works on such an extreme planet as Venus we may improve the accuracy and robustness in the models of the climate of the Earth. In particular the understanding of the complex physics of the clouds may be important for this.

 Venus Express Mission –Mission proposed as a re-use of the Mars Express Spacecraft to fit within the very limited budget available –Launcher, Ground system and operations facilities will be re-used as for Mars Express whenever possible –Scientific Instruments from Mars Express (3), Rosetta (2) and two new built ones –With only tree years from mission approval to launch, Venus Express is the fastest ever developed ESA science mission

 The Spacecraft

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 Science Payload

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 Venus Express taking off from Baikonur at 03:30 UTC on 9 November The Soyuz rocket placed the spacecraft in a sub-orbital trajectory which was circulized by a 20 s burn of the Fregat upper stage. After approximately one orbit a second Fregat burn of 14 min duration injected the spacecraft into a interplanetary trajectory. The injection was near perfect and only a minor adjustment by the spacecraft thrusters was necessary.

 Polar orbit 24 h period 66000km apocentre height km pericentre height control band Latitude of pc drifting slowly from 78 deg N at arrival to 90 deg N mid 2009 Pericentre height control band reduced to km late 2008

 Fantastic results! I can speak for a day or more on this but will only show three of the more important results from Venus Express. More will come by the following speakers.

 SpicaV/Soir measures HDO and H 2 O Aspera measures escaping water HDO/H2O ~ average This equals 240±25 times the ratio in the Earth’ ocean. As Deuterium is heavier than Hydrogen it cannot escape as easily. This is a strong indication that Venus has lost a large portion of water in the past ASPERA measures hydrogen and oxygen still escaping from the planet. The ratio is 2 to 1, thus corresponding to water!

 (J. Whatmore) MAG measures whistler waves The detection of whistler waves gives the final evidence of existence of lightning in the atmosphere, after a long debate based on indications from previous missions

 Is there active volcanism on Venus? The answer is YES! Smrekar (Science 2010) Virtis emissivity data overlayed on a radar map from the Magellan mission showing fresh surface in a region identified as a volcanic hotspot