Launch Countdown Begins for Europe's Venus Express Probe
ESA's Venus Express spacecraft and its Soyuz-Fregat rocket sit atop their launch pad at Baikonur Cosmodrome, Kazakhstan in preparations for a Nov. 8, 2005 launch.
Credit: ESA.

BERLIN (AP) - Scientists were counting down Tuesday for the blast off of a Russian booster rocket carrying a European-built probe aimed at exploring the hot, dense atmosphere around Venus.

The launch of the European Space Agency's Venus Express probe is planned for 10:33 p.m. EST (0333 GMT) Wednesday at the Russian-leased Baikonur Cosmodrome in Kazakhstan.

Venus Express was originally scheduled to go up Oct. 26, but the launch was postponed after checks revealed a problem with the thermal insulation in the upper section of the Soyuz-Fregat rocket. Once it separates from the rocket, scientists at ESA's mission control in Darmstadt, south of Frankfurt, plan to make contact with the probe.

"We've just had the pre-launch briefing and everything is in the green zone," said ESA spokeswoman Jocelyne Landeau. "Everything is ready for go."

The mission, Europe's first to Venus, is aimed at exploring the hot and dense atmosphere around the planet, concentrating on its greenhouse effect and the permanent hurricane force winds that constantly encircle it.

In addition, instruments on the probe will try to discover whether Venus' many volcanoes are active, and look at how a planet so similar to Earth could have evolved so differently.

"Venus is still a big mystery," Gerhard Schwehm, head of the planetary missions at ESA, said Monday.

Not only is Venus the nearest planet to Earth within the solar system, but the two share also roughly the same mass and density. Both have inner cores of rock and are believed to have been formed at roughly the same time.

But despite these similarities, the two have vastly different atmospheres, with Venus' composed almost entirely of carbon dioxide with very little water vapor. It is also the hottest surface of all the planets and lacks atmospheric pressure.

It will take 163 days, or roughly five months, for the $260 million (220 million Euros) probe to reach Venus. As a sister probe to ESA's Mars Express, launched in 2003,

Venus Express shares many instruments with Mars Express, a sister probe launched in 2003, and the Rosetta probe, sent last year and bound for a comet.

Venus Express is expected to begin its experiments in early June.

The last mission to Venus was Magellan, launched by NASA in 1989. It completed more than 15,000 orbits around the planet between 1990 and 1994.

Using radar, Magellan was able to map virtually all the surface of Venus, revealing towering volcanoes, gigantic rifts and crisp-edged craters.