Comet-chasing craft reaches destination after 10-year pursuit

Europe's Rosetta spacecraft reaches its final destination today after a decade-long journey into deep space that aims to place the first lander on a comet.

Rosetta will begin orbiting the Churyumov-Gerasimenko comet to glean information about the mass of dirty ice, dust and gas, according to the European Space Agency, which launched the probe in 2004. In November, it's due to send a smaller landing craft down onto the comet to take more measurements.

"This is the start of the real mission that Rosetta was built for - it's the kickoff of the real science phase," said Gerhard Schwehm, an ESA consultant and manager of the mission from its liftoff until he retired last year. "We're at the comet and now starting to monitor it and study it in detail."

Scientists hope to learn about the early evolution of the solar system by studying comets, which date back 4.6 billion years when the planets were forming. Researchers also are searching for organic molecules that represent the building blocks for life, which comets may have brought to Earth in its early years.

"It'll help us to model better the evolution of the planets out of the pre-solar nebula," Schwehm said by phone from ESA's mission control in Darmstadt, Germany. "There will be a lot of information that helps us understand how processes worked and what happened 4 1/2 billion years ago. It's information from the infancy of our solar system."

Comet Probe

The Rosetta mission is the first attempt to orbit and land a probe on a comet. ESA's first deep-space mission, Giotto, was sent to investigate Halley's Comet in 1986. The U.S. National Aeronautics and Space Administration has also launched two missions to study comets in the past 20 years.

Rosetta today is due to perform a final slowing maneuver shortly after 11 a.m. Darmstadt time. That will place the craft in an initial triangular orbit about 60 miles from the comet, according to Schwehm. Because signals from the spacecraft take more than 20 minutes to reach Earth, an announcement is likely about 11:30 a.m., he said.

Instruments aboard the orbiter and the lander will measure the chemical composition of the comet, its density and how strong the surface is. They'll also monitor gases and dust ejected by the comet. The landing craft, Philae is due to land around Nov. 11. It will be able to drill about 20 8 inches into the comet, Schwehm said.

Astrium, now part of Airbus Defence and Space, was the main contractor for the spacecraft launched on March 2, 2004. Since then, Rosetta has taken a circuitous route to Churyumov- Gerasimenko, using a gravitational "kick" from Mars and three from Earth to gain enough velocity to reach the comet.

Long Journey

The 6.4 billion-kilometer journey has taken the craft as far as a billion kilometers from Earth. It's now more than 400 million kilometers from Earth and about 540 million kilometers from the Sun, between the orbits of Mars and Jupiter, according to the ESA website. Rosetta is scheduled to orbit the comet until the end of 2015.

"We've had to be very patient," Schwehm said. "It took more than 10 years to get to our target, but we're there now."

The Paris-based European Space Agency was formed in 1973 and has 20 member countries, including the U.K., Germany and France.