By Paul Rincon
BBC News science reporter, Baikonur
Europe's first space mission to Venus has begun its five-month voyage to our closest planetary neighbour.
Venus Express lifted off on a Russian rocket from the Baikonur Cosmodrome in Kazakhstan at 0333 GMT on Wednesday.
The spacecraft will orbit Venus to study its atmosphere, which has experienced runaway greenhouse warming.
Scientists hope the two-year mission will shed further light on the mechanisms of climate change on our own world.
About 90 minutes after the probe blasted off, mission controllers said that it had left Earth orbit and was on its way to Venus. Shortly afterwards, they received the first signal from the craft.
"We've got a baby, it's talking to us, and it's got energy and power," said David Southwood, director of science for the European Space Agency (Esa).
"This is the beginning; it's going to be great."
The probe was launched on a Soyuz rocket topped by a Fregat booster, designed to propel the craft on a direct course to Venus.
It should reach its target in about five months, where it will enter an elliptical polar orbit.
It will fly to as low as 250 kilometres (156 miles) above the surface and to a height of 66,000 kilometres (41,250 miles).
"It's just such an exciting mission," said Prof Manuel Grande from the Rutherford Appleton Laboratory in Oxfordshire, UK.
"Earth is halfway between Venus and Mars, and when we put this together with Mars Express, it will tell us about the evolution of all three planets."
Venus Express copies the basic structure of the highly successful Mars Express spacecraft, launched in 2003.
Jerry Bolter of EADS Astrium, the spacecraft's main contractor, said the mission was put together in record time.
"It's the fastest turnaround for any spacecraft in Europe," he said.
"We now look forward to next year when we have a very challenging burn for the main engine to do."
Venus is almost identical in size to our planet, and is thought to have a similar composition. But there the resemblance ends.
A 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).
Surface pressure is about 90 times that on Earth. Several Soviet probes sent to land on Venus in the '60s were crushed before they could touch down.
By studying this hostile world, scientists hope to understand better how a warming future on our own planet might evolve.
"There are fundamental physics we want to do at Venus," said mission scientist Dimitry Titov. "We understand basic principles but we need Venus Express to propagate these details to Earth."