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Last Updated: Tuesday, 11 April 2006, 09:37 GMT 10:37 UK
Probe makes encounter with Venus
By Paul Rincon
BBC News science reporter


Europe's Venus Express probe has gone into orbit around our nearest planetary neighbour after a five-month journey.

Early on Tuesday, mission controllers fired its main engine to reduce its speed and allow it to be caught in the planet's gravitational pull.

Venus Express will orbit our nearest planetary neighbour for about 500 Earth days to study its atmosphere, which has undergone runaway greenhouse warming.

The mission should shed light on the mechanisms of climate change on Earth.

The main engine burn was initiated by controllers at the European Space Agency (Esa's) operations centre in Darmstadt, Germany at 0717 GMT.

Critical burn

The critical 49-minute-long manoeuvre was designed to reduce the spacecraft's velocity relative to Venus by 15%, allowing it to be pulled into orbit around the planet.

We want to see how the system works there because there are still many mysteries about Venus
Gerhard Schwehm, Esa

Mike Healy, UK director for EADS-Astrium, the spacecraft's main contractor, said it had to be perfect.

"If it burns for too long you could end up crashing into the planet," he explained.

At 0745 GMT, with its engine still firing, Venus Express disappeared behind the planet, severing contact between the craft and Earth.

After about 10 minutes, mission controllers picked up the spacecraft's signal - an early indication that the manoeuvre had worked and it was in orbit around Venus.

Scientists, engineers and officials in the control room clapped, cheered and embraced each other.

"It's a fantastic mission for us, we've finally reached Venus," said project manager Don McCoy.

'Euphoric'

British scientists and engineers involved in the mission watched the proceedings at the Royal Society in London via a live satellite link.

Artist's impression of the surface of Venus

Mission scientist Colin Wilson of Oxford University said he and his colleagues had been waiting for this moment for a very long time.

"Technically what we did today was a bit simpler than what we did at launch but because it was that much further away we were that much more nervous," he told the BBC News website.

"This was the last great high risk stage in the mission and it has really gone well."

Andrew Coates, a mission scientist at the Mullard Space Science Laboratory at University College London, said the spacecraft had done its burn at the right time and had slowed down in the predicted way.

"I think we can be euphoric about the way it has gone so far," he said.

Tight orbit

Venus Express will slip into a tight, elliptical orbit which will bring it to within 400km (250 miles) of the north pole.

The 140m mission aims to investigate how this world, so close to our own in size, mass, and composition, has evolved so differently over the last 4.6 billion years.

Though it is closer to the Sun than our own planet, a thick, highly reflective cloud layer means Venus absorbs less solar radiation than the Earth. One might therefore expect surface conditions on the two planets to be similar.

But Venus' dense, largely carbon dioxide, atmosphere acts as a blanket, trapping incoming solar radiation to heat the planet's surface to an average temperature of 467C (872F) - hot enough to melt lead.

Although Earth is unlikely to ever end up as hot, a build-up of greenhouse gases in the atmosphere could result in our own planet taking some uncomfortable steps toward the situation on Venus.

Our planetary neighbour's hostile climate could also hold answers to how global warming will affect Earth in future decades, helping to constrain computer models of climate change.

"Our prime objective is to study the processes that are going on inside Venus' atmosphere," Gerhard Schwehm, Esa's head of planetary missions, told the BBC News website.

"Nearly all the instruments give us information on either the composition of the atmosphere, temperature profile, or circulation. We want to see how the system works there because there are still many mysteries about Venus."

Mission scientists hope to learn what causes Venus' atmosphere to rotate much faster than the planet below. The craft will also study a swirling double vortex at the planet's north pole, to discover how it remains stable and where it gets its energy from.

Venus Express lifted off on a Russian Soyuz rocket from the Baikonur Cosmodrome in Kazakhstan on 9 November 2005.

Paul.Rincon-INTERNET@bbc.co.uk

PLANETS COMPARED
VENUS
EARTH
Distance from Sun 108,200,000km 149,600,000km
Diameter 12,103.6km 12,756.3km
Mass 0.82 Earth masses 1.0 Earth masses
Axial rotation period (sidereal day) 243 Earth days (retrograde) 23 hours 56 minutes
Year length 224.7 Earth days 365 days
Atmosphere 96% carbon dioxide
3% nitrogen
77% nitrogen
21% oxygen
Mean temperature 464C 15C
Atmospheric pressure at surface (kPa) 9,300 100
Moons 0 1
Global magnetic field No Yes




BBC NEWS: VIDEO AND AUDIO
Watch simulation of the Venus Express mission



SEE ALSO:
Doubt cast on Venus catastrophe
16 Mar 06 |  Science/Nature
Express mission to morning star
10 Nov 05 |  Science/Nature
Venus probe launched successfully
09 Nov 05 |  Science/Nature
Planet Venus: Earth's 'evil twin'
07 Nov 05 |  Science/Nature
Europe's Venus mission delayed
21 Oct 05 |  Science/Nature
Venus clouds 'might harbour life'
25 May 04 |  Science/Nature


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