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Venus passing in front of the Sun Venus is sometimes called the Earth’s twin planet. It is closest to the Earth in size and mass, and is our nearest neighbour. However, the resemblance ends there. Venus is the hottest planet in the Solar System and its surface is an extremely hostile environment. Its dense atmosphere is mainly carbon dioxide and there are several thick layers of cloud made of sulphuric acid. The atmosphere acts as a blanket, trapping incoming solar radiation and generating an average temperature of 464° Celsius – hot enough to melt lead! Missions to study the Venusian atmosphere show that this extreme greenhouse effect means there is little temperature variation between night and day. Venus Venus is the brightest object in the sky except for the Sun and Moon. The planet is often called the “morning star” or “evening star” because it is visible at dawn and dusk. Venus is named after the Roman goddess of beauty and love. To the ancient Romans, Venus was the patron goddess of vineyards and gardens – rather ironic, given the planet’s scorched surface! As Greek influence spread, Venus was attributed with the characteristics of the goddess Aphrodite, whose legendary beauty made her irresistible to gods and mortals alike. If you would like to know more about the Venus Express mission, try the following resources: WORLD WIDE WEB SITES www.esa.int/venus www.uk2planets.org.uk www.mssl.ucl.ac.uk/www_plasma/ missions/vex.html www.nineplanets.org www.esa.int/marsexpress www.esa.int/rosetta www.atm.ox.ac.uk/project/virtis www.venus.wisc.edu BOOKS Venus Sir Patrick Moore Cassell Illustrated, 2002 The Cambridge Photographic Guide to the Planets Frederic W Taylor Cambridge University Press, 2001 Venus Revealed David Grinspoon Perseus Books, 1998 Empire of the Sun John Gribbin and Simon Goodwin Constable, 1998 IMAGES Astrium (Mars Express) NASA/JPL/MSSS (Mars) NASA/JPL/Arizona State University (Evidence of Flow) ESA NASA/JPL/AOPP (Venus) Venus is the second planet from the Sun and, when it is precisely aligned with the Earth, we can see it pass in front of the Sun’s disk. These alignments are rare because the orbital plane of Venus is slightly tilted relative to that of the Earth. The Transit of Venus in 2004 was the first time in 121 years that the phenomenon had been visible. The next transits are in 2012 and 2117. Historically, Transits of Venus are important because they were used to calculate the distance between the Earth and the Sun. The transit of 1769 was the reason for Captain James Cook’s epic voyage around the world which also led to a wide range of discoveries about Australia, New Zealand and the islands of the Pacific. The Science and Technology Facilities Council operates world-class, large-scale research facilities; supports scientists and engineers world-wide; funds researchers in universities and provides strategic scientific advice to government. Venus Express is also closely related to the comet chaser, Rosetta, and uses copies of its detectors to study the Venusian magnetic field and the chemical composition of the planet’s atmosphere. The Council’s Science in Society unit offers a wide range of support for teachers, scientists and communicators to facilitate greater engagement with STFC science which includes astronomy, space science, particle physics and nuclear physics: For schools • Free Publications and resource guides suitable for teaching ages 10-18. Go to www. scitech.ac.uk - Public and Schools - Schools and Education - Resources • Funding schemes for projects and school visits. Go to www.scitech.ac.uk - Public and Schools - Funding • A Moon rock and meteorite loan scheme. Go to www.scitech.ac.uk - Public and Schools - Schools and Education - Loan Scheme • Visits to STFC’s UK laboratories in Cheshire, Oxfordshire and Edinburgh plus CERN in Geneva. Go to www.scitech.ac.uk - Public and Schools - Visits and Events • Researchers in Residence. Teachers are placed in partnership with young scientists who have been trained to support the teacher, act as role models and introduce their research. Go to www.researchersinresidence.ac.uk For scientists • Communication and media training courses; funding schemes and Fellowships for public engagement. Go to www.scitech. ac.uk - Public and Schools - Fellowships and Communications Training For further information telephone 01793 442175 or email [email protected] Venus Express is the European Space Agency’s first mission to Venus. The spacecraft shares more than a speedy-sounding name with Red Planet explorer, Mars Express. The basic structure of both spacecraft is identical, as is much of the scientific instrumentation. Venus Express uses copies of Mars Express sensors to study the Venusian atmosphere at different altitudes, monitor the plasma environment and to take images of cloud patterns. Air-pressures on Venus are also extreme, averaging 92 atmospheres. This is approximately the same pressure as you would experience 1 kilometre beneath the sea surface on Earth. The Venusian atmosphere once contained large quantities of water but it is now completely dry, unlike its twin planet. Venus lies 41 million kilometres closer to the Sun than Earth and is in a zone that’s too hot for water to last long. Mars is 78 million kilometres further away from the Sun than us and has an average surface temperature of –50 degrees, so cold that any water is locked away as ice. However the Earth is positioned in what’s known, after the well-known fairytale, as the “Goldilocks Zone”. Its distance from the Sun is just right for water to exist in liquid form – probably a necessary condition for life to evolve. This sharing of technology meant that Venus Express could be developed on a rapid timescale that’s unprecedented. Most planetary missions are developed over several years but plans for Venus Express were approved at the end of 2002, just three years before its launch in late 2005. Venus Express has been so successful that its original mission, which was due to last 500 days, has been doubled in length to 1000 days. It is due to finish in May 2009. Venus spins very slowly – once every 243 days – this means that even with its extended mission, Venus Express will have only orbited the planet for 4 Venusian days. phere in the hemis ultr avi ol with area map pe db yV et ress Exp ob Gl iew al v o ’s us e rn uth ap llan m us en Ve n ge Ma of Venus in the in frar ed a b c Venus has a similar interior to Earth, with a partially molten core, mantle and crust, so why does it not have a similar magnetic field? It had one for a billion years, generated by convection currents in the core, driven by left over heat after Venus’s formation. When that energy ran out 3.5 billion years ago, the field disappeared. This didn’t happen on Earth. The reason for this is a mystery, but the lack of a magnetic field means that Venus is unprotected from the Solar Wind. This stream of electrically charged particles hits the upper layers of Venus’s atmosphere, colliding with atoms and molecules and carrying them into space. UCL’s Mullard Space Science Laboratory and STFC’s Rutherford Appleton Laboratory have helped develop the ASPERA-4 instrument which is investigating these interactions and the rate at which atmospheric gases are stripped away. Scientists from Imperial College London have helped build the magnetometer that is studying the weak magnetic effects produced where the Solar Wind meets the planet’s atmosphere. Recent results from Venus Express show that Earth and Venus started off with very similar atmospheres suggesting that Venus was once a very wet planet; however, water no longer exists on the surface and Venus continues to get dryer as the Solar Wind and cosmic radiation strip away hydrogen, oxygen and helium from the atmosphere much faster than happens on Earth. 3D Perspective View of Maat Mons by Magellan Imaging Radar © JPL d Venus’s thick cloudy atmosphere means it is difficult to see the surface using normal cameras. Between 1990 and 1994, the Magellan spacecraft orbited Venus and used radar to map the planet’s surface. This showed two large continents and other highland plateaux, separated by lowland areas where liquid may once have flowed. There are four mountain ranges and numerous volcanoes, plus areas of broken terrain called “tessera” that suggest Venus’s surface is moving. Venus has a complex atmosphere with distinct layers and turbulent weather systems. There is a thick cloud layer of sulphuric acid droplets concealing lower patchy cloud cover, similar to cumulus clouds on Earth. Venus Express is using infrared wavelengths to penetrate the outer layers and map the whole atmosphere. Clouds on Venus move at about 350 km/h and the whole atmosphere rotates 60 times faster than the planet itself! Venus Express is measuring atmospheric temperature differences as air moves round the planet and through different altitudes. It is also measuring concentrations of sulphuric acid, sulphur dioxide and other chemicals. VENUS’S ATMOSPHERE Venus has a thick crust, which prevents continental drift, so the cracking and buckling found must be caused by different processes to the Earth’s plate tectonics. 96% CARBON DIOXIDE Venus like Earth, shows relatively few impact craters, which suggests its surface is “young” in geological terms (around 500 million years old). 1% TRACE OTHER GASES (Including sulphur dioxide and water vapour) The VIRTIS instrument carried by Venus Express is looking for evidence of volcanic activity by measuring the concentrations of gases in the atmosphere and and is trying to identify any volcanic hotspots. Scientists from Oxford University have collaborated in building an infra-red sensor, VIRTIS, to study the bottom 100km of the atmosphere – looking at the evolution and movement of weather features. 3% NITROGEN (a) A false colour mosaic of the Venusian surface, composed from about 1000 individual Venus Monitoring Camera (VMC) images taken in April and August 2007. (b) This composite image of Venus is a combination of ultraviolet images obtained by the Venus Monitoring Camera (VMC) and infrared images obtained by the Visual and Infrared Thermal Mapping Spectrometer (VIRTIS) on board ESA’s Venus Express. (c) Infrared views of south polar double-vortex (d) While Earth has a planetary magnetic field, which can deviate the flow of solar wind, Venus (and Mars) don’t. Gases in the upper atmospheres of these planets are ionised, and can thus interact with the solar wind. Previous missions have found giant vortices, like hurricanes, funnelling air downwards at the poles. The northern vortex appears to have a double ‘eye’ surrounded by much colder air. Scientists do not understand why this occurs.