By Paul Rincon

BBC News science reporter



The Virtis image shows a "vortex" over the south pole

They show the hothouse planet's south pole from a distance of 206,452km.

Mission scientists are already intrigued by a dark "vortex" feature which can be clearly seen in one image.

Venus Express will orbit the planet for about 500 Earth days to study its atmosphere, which is thought to have undergone runaway greenhouse warming.

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

Polar vortex

Experts had previously suspected the south pole might have a vortex feature; a vast vortex with an unusual double-eye feature has already been observed over the planet's north pole.

But the south polar region has scarcely been observed.

"We can see there is a twister here that is similar to that which we know from the north pole," said mission scientist Horst Uwe Keller.

The VMC imaged the south pole in ultraviolet

European Space Agency (Esa) officials said the pictures were "surprisingly clear", with "unexpected detail".

They were captured on 12 April by the Virtis (Visible and Infrared Thermal Imaging Spectrometer) and Venus Monitoring Camera (VMC) instruments onboard, as the spacecraft passed below the planet in an elliptical arc.

The false-colour Virtis composite image shows Venus' day side at left and night side at right, and corresponds to a scale of 50km per pixel.

Night half

The spectacular night half was taken via an infrared filter and shows dynamic spiral cloud structures in the lower atmosphere, around 55km in altitude.

The darker regions correspond to thicker cloud cover, while the brighter regions correspond to thinner clouds.

Mariner 10 took this image of the north polar vortex in the 1970s

Venus Express successfully executed a 50-minute main engine burn on Tuesday designed to slow its speed enough to be captured by the planet's gravitational pull.

As the spacecraft tightens its orbit in the coming months, scientists expect it to capture more detailed and revealing images of the planet.

Scientists hope to learn how Venus, which is similar to Earth in size, mass and composition, evolved so differently over the last 4.6 billion years.

The mission is the first to be sent to the planet in 15 years.

Paul.Rincon-INTERNET@bbc.co.uk