The planet Venus is most remarkable for the many ways it resembles Earth and the equally many ways it is wildly different. Much about the Venus, either way, remains mysterious.
A mission to our cloud-shrouded sister planet would help lift its many veils. One possible mission, planned by the European Space Agency, is called Venus Express and would launch in 2005. At an annual meeting of the Royal Astronomical Society earlier this week, Fred Taylor of the University of Oxford discussed Venusian mysteries that might be explored by the mission.
Venus is Earth's nearest planetary neighbor, similar in size and mass. Its hot climate could hardly be more different, however. The surface is so toasty that it can melt metal. Many researchers point to Venus as a classic case of runaway greenhouse effect, yet they can't explain why it has occurred.
One puzzle is that despite the planet's proximity to the Sun, Venus absorbs less solar heat than the Earth does.
The surfaces of the two planets have also evolved quite differently. Venus has vast, smooth plains not seen on Earth. Extensive volcanic activity produces dense cloud layers with an exotic, sulfur-rich composition.
Most puzzling of all is the atmospheric circulation which features hurricane force winds at high levels that sweep around Venus in just four days -- remarkably rapid for a planet that only rotates once every 243 Earth days.
"The planet's weather systems and climate characteristics cannot be understood by comparison with Earth," Taylor said. "The failure of extrapolated terrestrial models to account for Venus' behavior has wide implications in fields ranging from solar system evolution to climate forecasting on Earth."
Venus Express is proposed to be launched on a direct trajectory to Venus with a Soyuz-Fregat rocket from the Baikonur Cosmodrome in Kazakhstan. After a flight of about 150 days, it would be maneuvered into a polar orbit above the planet, where it would study the surface and atmosphere for two Venus years, or 450 Earth days.
"Venus Express is a strong candidate to be part of the next wave of Venus exploration, including Japanese and probably American space missions, which will probe the environment of this mysterious planet," Taylor said.
NASA has no firm plans for a mission to Venus, but the agency has discussed sending a robot after 2007 to grab surface samples and return them to Earth. A proposed spacecraft to orbit Mercury later in the decade would possibly make a Venus flyby en route.
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