The European Space Agency is set to launch a spacecraft to Venus. It will be the first mission to the swelteringly hot and corrosive planet in 15 years.
Called Venus Express, it is scheduled to lift off aboard a Soyuz rocket from Baikonur, Kazakhstan, on 26 October. When it arrives at Venus in April 2006, it will study the planet from a polar orbit stretching from an altitude of 250 to 60,000 kilometres.
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Seven instruments will scrutinise the planet at a range of wavelengths. Astronomers hope to understand how a planet that has more in common with Earth than any other in terms of distance from the Sun, size and mass could have evolved into such an inhospitable world.
Temperatures hover at 450掳C, while the thick, carbon dioxide atmosphere produces crushing surface pressures 90 times those on Earth and sulphuric acid rains from the sky. 鈥淲e鈥檙e still struggling to understand why Venus is so radically different from Earth,鈥� says Fred Taylor, an astronomer at the University of Oxford, UK.
Mysterious vortices
The mission will focus mainly on the composition and temperature of Venus鈥檚 atmosphere. It rotates 50 to 60 times faster than the planet itself, which spins just once every 243 days and in the opposite direction to Earth. In particular, researchers will study mysterious hurricane-like vortices above the poles.
Mission scientists also hope to probe down to the surface, where the clouds are thinner. This thinning was discovered during a flyby of Venus with the Galileo spacecraft in 1990. Patches of near-infrared light seen on the planet鈥檚 dark side were interpreted to be the planet鈥檚 own heat glowing through relatively thin clouds. 鈥淭he surface is so hot, it鈥檚 effectively backlighting the thinner clouds,鈥� says Taylor.
The surface will also be scanned for active volcanism, hinted at by the presence of sulphuric acid in the atmosphere, but never seen. Venus boasts the most volcanoes of any planet in the solar system. Nearly 90% of its surface is covered by basaltic lava flows. Based on the size and number of impact craters, the lava appears to be about 500 million years old.
This age suggests that, unlike Earth, Venus does not have multiple rocky plates that constantly move and collide over the hot, soft rock in the planet鈥檚 core. On Earth, plate tectonics enables heat to escape from the core.
Instead, Venus鈥檚 surface may have been made of a single plate that was destroyed 500 million years ago when enough heat built up in the planet鈥檚 interior. Such 鈥渃atastrophic resurfacing鈥� may be a cyclic process, says Dmitri Titov, a team member at the Max Planck Institute for Solar System Studies in Katlenburg-Lindau, Germany.
But local volcanic activity probably goes on all the time, says Taylor, and the gases belched out in the process would 鈥済o a long way toward explaining Venus鈥檚 extreme climate鈥�.
Rapid development
ESA developed the 聙220-million-mission in just three years. This was possible as it is based largely on the design and instrumentation of the agency鈥檚 Rosetta mission 鈥� currently on track to reach a comet in 2014 鈥� and its Mars Express orbiter.
But this approach may also have drawbacks. For example, Venus Express carries a spectrometer called the PFS, which has recently failed on Mars Express. But Don McCoy, the mission鈥檚 project manager, says the instrument probably stopped working because it simply wore out. He says Venus Express mission officials may carefully select the times when the PFS takes data 鈥渢o make sure we don鈥檛 use it up too soon鈥�.
The mission is the first dedicated to Venus since NASA鈥檚 Magellan spacecraft mapped the surface of the planet in 1990. Venus Express is scheduled to operate for about 500 Earth days 鈥� the equivalent of two rotations of Venus 鈥� but it has enough fuel to last 1000 days.
