Europe's first mission to Venus was successfully launched Wednesday from the Baikonur cosmodrome in Kazakhstan and emitted a first signal at the start of its 163-day journey to the turbulent planet.
Venus is about the same size but much hotter than Earth
The Venus Express probe separated from the Soyuz Fregat carrier around 90 minutes after the 3:33 a.m. GMT blast-off on the first expedition to Earth's closest neighbour in over 10 years.
"A perfect mission," said Jean-Yves Le Gall, head of Starsem, which was in charge of the launch, after the take-off.
Off to Venus
The probe soon emitted its first signal.
"The baby cried," said Jean-Pierre Cau of EADS Astrium, which built the spacecraft's propulsion system. "Venus Express has begun its operational mission."
Venus Express will explore the unusual stormy atmosphere and runaway global warming on Venus in the hope of better understanding Earth's greenhouse-gas problem.
Similar, yet differe n t
Venus, the second planet from the Sun, is similar in size, mass and age to Earth but has a vastly different and ferociously hot weather system.
Also known as the Evening Star, thanks to the bright light it reflects from the Sun, the planet is blanketed by thick clouds of suffocating gas driven by often hurricane-force winds and a surface pressure and temperature high enough to crush and melt lead.
The planet's clouds reflect back 80 percent of the Sun's radiation and absorb another 10 percent, leaving just 10 percent to filter down to the surface.
Would it look differently on Venus?
But the clouds provide such effective insulation the surface zone becomes a pressure cooker capable of melting metal.
"Venus has no surface water, a toxic, heavy atmosphere made up almost entirely of carbon dioxide (CO2) with clouds of sulphuric acid, and at the surface the atmospheric pressure is over 90 times that of Earth at sea-level," the ESA notes.
The planet's searing surface temperature of 477 Celsius (890 Fahrenheit) -- the hottest in the Solar System -- and immense atmospheric pressure have caused many previous missions to fail or send data streams lasting only minutes before their instruments were crushed.
Ra n ge of tests pla n n ed
It is hoped, however, that the 1.27-ton unmanned Venus Express orbiter will be able to use seven powerful instruments on board to map the planet's surface and weather system, looking at temperature variation, cloud formations, wind speeds and gas composition.
The craft is scheduled to arrive off Venus in April, when it will be placed in an elliptical orbit, swooping to as low as 250 kilometers (156 miles) above the surface to a height of 66,000 kilometers.
Mars Express is already on duty
The orbiter, whose total mission costs are 220 million euros ($264 million), has enough fuel to operate for 1,000 Earth days, according to ESA officials.
The craft's sister orbiter Mars Express is currently on a mission circling Mars.