ESA readies Venus Express for launch
Mission to unravel mysteries of our 'evil twin'
The European Space Agency, undeterred by the loss of Cryosat, is pushing ahead with plans to launch its Venus Express mission, Europe's first to Venus, later this month. The spacecraft will blast off from the Baikonur Cosmodrome in Kazakhstan on 26 October on a journey that will take it approximately five months.
Much is still mysterious about Venus. "You can think of Venus almost as being Earth's evil twin," said Dr. Andrew Coates from the Mullard Space Science Laboratory at UCL.
But our supposed twin is actually very different, the similarity in size and rocky composition really being the only things the two planets have in common.
It has an odd, retrograde rotation so slow that one Venus day is around 250 Earth days long. The planet is wrapped in a thick atmosphere which makes its surface pretty much invisible in the optical spectrum, and means the surface pressure is around 100 times than of Earth's.
The clouds, which speed round the planet in just four Earth days, are highly acidic, and the surface temperature is hot enough to melt lead.
Many other questions about the planet, which for a long time was assumed to be very similar to Earth, remain unanswered. One of the main questions is how did our twin planet end up so strikingly different to Earth, and can we learn anything from studying it that will help us understand our own environment?
Venus Express is based on the same design and uses much of the same technology as the Mars Express mission, and the Rosetta probe. Recycling the technology like this means ESA has been able to put the mission together for a relatively modest budget of £140m, inside four years.
Many of the instruments are different, however, and the craft has been tweaked to help it survive the different requirements of a Venusian orbit.
The craft is designed to find out more about the nature and evolution of Venus's atmosphere, as well as to peer through the thick clouds to study the planet's surface. Scientists hope its experiments will help explain how exactly Venus got to be quite so different from Earth.
One crucial difference is that Venus has no magnetic field. This leaves its upper atmosphere vulnerable to the pounding of the solar wind. Scientists theorise that this constant bombardment has been stripping the upper atmosphere away, in the same way as it has on Mars.
Venus Express will be positioned to map the background magnetic field in the region, to track how the solar plasma interacts with the atmosphere. The same instruments will help scientists determine what happened to the water, widely believed to have been present when Venus was young.
The Venus Express orbiter will also be looking for evidence of current volcanic activity. "We strongly suspect that it is volcanically active," said Professor Fred Taylor of Oxford University, "but we don't really know. We will be able to find out with Venus Express."
Professor Taylor adds that the mission might help determine what the peaks of the planet's volcanos are covered in. All the big mountains have "snowy" peaks starting at a the same height. The "snow" was originally thought to be pure tellurium, but this is very rare, and the thought was discounted.
"Later it was fashionable to think of the peaks as being covered in iron sulphide (Fool's Gold)," said Taylor. "But the latest thinking is that it is iron chloride, which is more stable."
The mission should also establish whether or not there is lightning on Venus. ®
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