Europe sends a probe to solve riddle of Venus

First mission to our nearest neighbour by the European Space Agency could shed light on Earth's future. By Severin Carrell

For millennia, Venus has enchanted romantics and mystified astronomers. But now its secrets are about to be revealed by a small aluminium box of gadgets weighing a little more than a ton.

The final countdown will begin next week for the launch of Europe's first expedition to Earth's nearest planetary neighbour - a two-year mission to investigate one of our solar system's greatest scientific enigmas.

The third-brightest object in the heavens after the Sun and Moon, and known for centuries as the Morning Star, Venus is effectively Earth's twin. It was named after the ancient Roman goddess of love. Writers from Ovid to Dylan Thomas have seen it as a symbol of beauty.

Yet, in fact, it is cursed by a climate as hostile as that of any planet in the solar system. It is the roughly the same age, size and mass as the Earth and, like Earth, it has a magnetic core and a rocky surface resting on a mantle of molten rock. It may even once have had vast oceans of water. But there the similarities end.

Over the past 4,000 million years, while the Earth has evolved into a benign home to life, Venus has become shrouded in a dense, hot and noxious cloud of gases that rises 50 miles above the planet's surface. Its atmosphere presses down with a crushing force 90 times as great as that on Earth - which accounts for the failure of most US and Soviet Union missions there.

Next week, the European Space Agency's first attempt to reach Venus will be officially unveiled in London. By penetrating its thick veils of gas, researchers hope to uncover secrets which could help predict the threats of climate change, and transform understanding of the solar system.

"To this day, if we do the sums and transfer the models from Earth to Venus, Venus ought to be much more Earth-like than it is, which is why it deviates so much from our expectations," said Professor Fred Taylor of Oxford University, a chief proponent of the Venus Express mission.

The contrast between the two planets is extreme. Venus is permanently encircled by hurricane-force winds, and endures an atmosphere as hot as 464C. Its gravity is unexpectedly light and it rotates extremely slowly - backwards. Each Venusian day lasts for 243 days on Earth.

Soon after 26 October, the Venus Express will blast off aboard a Russian-built Soyuz rocket from Baikonur cosmodrome in Kazakhstan for a flight expected to last 162 days. About five days after it arrives in March or April next year, and has unfurled its pair of eight-metre-long solar panels, the spacecraft will spend two weeks manoeuvring into its working orbit, before beginning its work. The spacecraft itself is the interplanetary equivalent of a kit car - built chiefly using spare parts and unused duplicate instruments made for its predecessor, Mars Explorer, and off-the-shelf equipment.

Venus Express is due to spend the next 16 months gathering data about the planet's surface and probing its atmosphere.

And, if its main mission succeeds, it has enough fuel for another 500 days of data-gathering.

The Venusian surface is, in planetary terms, very recent. Scientists believe it is periodically "wiped clean" by long, planet-wide episodes of volcanic activity. The last one was some 500 million years ago.

That, said Professor Taylor, could also be the source of the planet's hot, noxious atmosphere. "This object was formed at the same time as Earth and Mars, from the same stuff, so there are questions about what is going on inside these planets, including the one we're sitting on."

VENUS BY NUMBERS

42,000,000 miles from Venus to Earth

464 Venus's surface temperature in Celsius

220 the wind speed in mph in Venus's upper atmosphere

243 Earth days in a Venusian day

7,521 Venus's diameter in miles