Venus' atmosphere is composed chiefly of carbon dioxide (CO2)Observations of the planet Venus might assist efforts to tackle the threat of climate change here on Earth.
Data from a European probe orbiting Venus paints a picture of a planet that may once have been like Earth, but later evolved in a very different way.
Venus has undergone runaway greenhouse warming, where trapped solar radiation has heated the surface to an average temperature of 467C (872F).
New results from the Venus Express mission appear in Nature journal.
In size, mass and composition, Earth and Venus are remarkably similar. Venus is closer to the Sun, but this alone does not explain the differences with Earth.
Venus lacks the Earth's magnetic shield, which means that its atmosphere feels the full onslaught of the solar wind - a stream of charged particles from our star - and cosmic radiation, and has done so for billions of years.
Lost water
The absence of this shield means that hydrogen, helium and oxygen are blown away by the solar wind much faster than happens on Earth.
The scientists think that Venus may once have held copious amounts of water on its surface.
Mission guide: Venus Express
But the solar wind removed most of it during the first billion years or so after the formation of the Solar System.
Professor Fred Taylor, from the University of Oxford and a scientist on the mission, said: "It is now becoming clear why the climate on Venus is so different to Earth, when the planets themselves are otherwise quite similar.
"Our new data make it possible to construct a scenario in which Venus started out like the Earth - possibly including a habitable environment, billions of years ago - and then evolved to the state we see now."
Mitigating the threat
Ian Pearson, the UK minister for science and innovation, said: "Understanding the influencing factors of global warming on Venus could help us in mitigating the threat here on Earth."
British scientists and engineers are playing a leading role on the European Space Agency (Esa) mission.
Venus Express arrived at the planet in April 2006Venus Express has also confirmed the presence of lightning on the planet. The idea of lightning on Venus was once considered controversial, but the magnetometer instrument on Venus Express has now put all doubts to one side.
Indeed, the data suggests that lightning is more common on Venus than it is on Earth.
Previous observations have revealed a vast rotating vortex of clouds with a "double-eye" feature at Venus' north pole. Researchers have now found evidence for similar features at the south pole, but these rotate slightly faster.
Researchers do not yet have any evidence for active volcanism on the Venusian surface, something that has been proposed in the past.
Venus Express was launched from the Baikonur Cosmodrome in Kazahstan in November 2005. It reached orbit around Venus in April 2006.
BBC NEWS | Science/Nature | Venus offers Earth climate clues
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