A European-built probe blasted off early Wednesday on a five-month journey to explore the hot, dense atmosphere of Venus.

The European Space Agency's Venus Express probe, which lifted off from the Russian-leased Baikonur cosmodrome in Kazakhstan, should take 163 days to reach Venus.

Mission control activated the $260 million probe's instruments after it left orbit and immediately picked up a signal.

"The mission is an outstanding success," Gaele Winters, director of ESA's operations in Darmstadt, told reporters. "We had a perfect launch, the instruments are switched on, the solar panels are deployed, everything is working."

Shortly after activation, ESA received its first congratulatory note, sent from the Pasadena, Calif.-based Planetary Society, which had monitored the launch from NASA's Jet Propulsion Lab.

Venus Express is Europe's first mission to Earth's closest neighbor in the solar system, often referred to as the "Morning Star" because it is visible near the horizon shortly before dawn. The probe was originally scheduled to go up Oct. 26. The launch was postponed after checks revealed a problem with the thermal insulation in the upper section of the Soyuz-Fregat rocket.

The mission aims to explore the planet's atmosphere, concentrating on its greenhouse effect and the permanent hurricane force winds that constantly encircle it at high altitudes.

The probe's seven instruments, including a spectrometer to measure temperatures and analyze Venus' atmosphere and a special camera, will try to determine whether Venus' many volcanoes are active and examine how a planet so similar to Earth could have evolved so differently.

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

Over the next three days, mission controllers will continue initial tests of the instruments and then allow the probe to continue its planned path toward Venus, which it is expected to reach in April. It will then be slowed down to enter into orbit around the planet and begin the initial stages of gathering data in June.

"We hope to see the first results in early July," said Schwehm, noting the probe will remain active for slightly more than a year. "We hope to know more then than we do now.

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

Despite those similarities, the two have vastly different atmospheres, with Venus' composed almost entirely of carbon dioxide and very little water vapor, resulting in the planet's crushing density. It also has the hottest surface of all the planets.

The last mission to Venus was NASA'S Magellan, launched 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.