Craft flies in to embrace Earth’s evil twin sister

The Times April 12, 2006

By Mark Henderson, Science Correspondent

A BRITISH-BUILT spacecraft reached Venus yesterday on a two-year mission to explore the Earth’s closest planetary neighbour, ending a 250 million-mile journey that started in Hertfordshire.
Venus Express, the first probe sent in 16 years to what is sometimes called the Earth’s “evil twin”, entered orbit soon after 9am after firing its engines for 50 minutes to slow down and allow itself to be captured by the planet’s gravity.

Scientists at the Royal Society in London cheered and clapped as mission control in Darmstadt, Germany, confirmed that the orbit had been achieved successfully. The team had earlier endured an anxious ten-minute wait as the probe passed behind Venus and out of touch with Earth. Had the engine burn ended prematurely, the craft would have shot off into space, while too much power would have sent it crashing into the planet.

Andrew Coates, a mission scientist from the Mullard Space Science Laboratory at University College London, likened the operation to a “handbrake turn” executed to perfection. “I’m euphoric — for now, so far so good. We are about to enter a new chapter of exploration.”

Venus Express will be making observations today and tomorrow as it swings past the planet’s south pole, before taking the rest of the month to settle into its final orbit. The first scientific results are expected next week. Over the next 500 days, the probe will loop around the planet hundreds of times, passing as close as 155 miles to the surface and collecting data that should transform astronomers’ understanding of Venus. The entire mission, however, will occupy only two Venusian days: the planet takes 243 Earth days to rotate once.

Although Venus is similar in size to Earth, its dense atmosphere generates crushing pressure 90 times higher than Earth’s, and as it is 96 per cent carbon dioxide the planet has experienced a runaway greenhouse effect that heats the surface to an average of 465C (869F). As if these conditions were not inhospitable enough, it also has thick clouds of sulphuric acid vapour but virtually no oxygen or water, the two prerequisites of life on Earth.

“Venus is our nearest neighbour but it is also our worst nightmare,” Dr Coates said. “It’s really a Hell-on-Earth planet: it has evolved into our twisted sister or evil twin.”

This evolutionary path is thought to owe much to the planet’s lack of a magnetic field, which on Earth protects against the ravages of the solar wind — the stream of particles thrown out by the Sun.

The processes that created Venus’s unpleasant environment remain poorly understood despite more than 20 missions, the most recent in 1990, and instruments on Venus Express should provide scientists with much firmer answers.

Insights into Venus could even help to refine climate and weather models on Earth. Professor Fred Taylor, of the University of Oxford, one of the mission architects, said: “Venus really is Earth’s twin, born at the same time and of similar size, but behaving in a different way. Some of the reasons why Venus acted the way it did may explain some of the problems we are having on Earth.”

The probe cost £140 million. It re-used much of the technology flown on the hugely successful Mars Express mission. It is also remarkable for the short time that it has taken to fly: the mission was approved by the European Space Agency in 2002. It was built in Stevenage by the satellite company EADS-Astrium, and launched from the Baikonur Cosmodrome in Kazakhstan last November.

David Southwood, the agency’s director of science, said: “It all comes back to the basic question of how did we get here . . . It’s essential to go into space to answer that, and Venus is one more step along the route.”

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