After 10 years spent traveling more than 6 billion km through space, Europe’s Rosetta mission has arrived at its destination – 67P/Churyumov-Gerasimenko – becoming the first spacecraft in history to rendezvous with a comet.

Flying some 405 million km (250 million mi.) from Earth, Rosetta is now ready to swivel into an elliptical orbit around 67P/Churyumov-Gerasimenko, where it will spend the next two months searching for a landing site for the mission’s small Philae robotic probe.

"After 10 years, five months and four days traveling towards our destination, looping around the Sun five times and clocking up 6.4 billion km, we are delighted to announce finally ‘we are here,’" says Jean-Jacques Dordain, director general of the European Space Agency (ESA), which is leading the Rosetta mission along with prime contractor Airbus Defense and Space.

With Philae expected to descend to the comet’s surface in early November, the orbiter and lander will spend more than a year studying primary material from 67P/Churyumov-Gerasimenko that could give scientists a glimpse at what the Solar System looked like more than 4.6 billion years ago.

Since its 2004 launch atop an Ariane 5 rocket from the Guiana Space Center in Kourou, Rosetta has made three gravity-assisted flybys of Earth and one of Mars on its way to rendezvous with the comet. This complex trajectory has seen Rosetta pass by the asteroids Steins and Lutetia, obtaining unprecedented views and scientific data on both.

After waking from deep-space hibernation at roughly 9 million km from 67P/Churyumov-Gerasimenko in January, Rosetta spent the past seven months activating 11 scientific instruments aboard the spacecraft and another 10 riding on the small lander it is carrying.

The Aug. 6 rendezvous saw the last of a sequence of 10 orbital maneuvers that began in May to adjust Rosetta’s speed and trajectory in line with those of the comet, slowing from 775 meters per second to just 1 meter per second.

ESA says each of these maneuvers was critical, and that had any one failed, the rendezvous would have been impossible.

"Today’s achievement is a result of a huge international endeavor spanning several decades," says Alvaro Gimenez, ESA’s director of science and robotic exploration. "We have come an extraordinarily long way since the mission concept was first discussed in the late 1970s and approved in 1993, and now we are ready to open a treasure chest of scientific discovery that is destined to rewrite the textbooks on comets for even more decades to come."

Measuring 2.8 x 2.1 x 2.0 m with two 14 meter-long solar panels, the Rosetta spacecraft carries instruments for remote sensing and radio science, and to study the composition, mass distribution and dust flux of the comet’s nucleus, as well as its plasma environment and interaction with solar wind. These instruments are situated on one side of the spacecraft, which will permanently face the comet during the mission’s operational phase.

For now, the 100-kg (220-lb.) Philae lander is flying on the orbiter opposite a large high-gain antenna dish. When it is deployed to the comet, two harpoons will anchor it to the surface as self-adjusting landing gear ensure it stays upright, even on a slope. At that point the lander’s feet will drill into the ground and secure it to the comet, where it is designed to dig beneath the surface and gather clues to the primitive solar system, including the possible origin of water on Earth.

In addition to being the first spacecraft ever to orbit a comet’s nucleus and land a probe on its surface, Rosetta is also the first to fly alongside a comet as it speeds toward the inner Solar System at about 55,000 km per hour.

Rosetta is also the first space mission to go beyond the main asteroid belt and rely solely on solar cells for power generation, rather than conventional radio-isotope thermal generators. The new technology used on the orbiter’s twin solar panels allows the mission to operate more than 800 million km from the Sun, where sunlight levels are only 4% of those on Earth.

"This is a great moment for the whole space community, and also for ESA as well as our engineers and technicians at Airbus Defense and Space," says François Auque, head of Space Systems. "Our robust spacecraft and the extraordinary performance of our hardware components underline what is meant by ‘quality.’"

In recent months, as Rosetta captured images of the comet on approach with its onboard OSIRIS camera, the mission has revealed the unusual shape of 67P/Churyumov-Gerasimenko. Pictures snapped about 12,000 km from the comet show the nucleus comprising two distinct segments joined by a "neck," giving it what ESA describes as a "duck-like" appearance.

"Is this double-lobed structure built from two separate comets that came together in the Solar System’s history, or is it one comet that has eroded dramatically and asymmetrically over time?" asks Matt Taylor, ESA’s Rosetta project scientist.

In addition to these images, Rosetta has gathered early measurements using its Microwave Instrument for the Rosetta Orbiter (MIRO) that suggest the comet is emitting water vapor at about 300 milliliters per second. Likewise, the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) measured the comet’s average temperature to be about -70 deg. C, indicating that the surface is mainly dark and dusty rather than clean and icy.

Today, Rosetta is just 100 km from the comet’s surface, but it will move closer over the next six weeks to describe two triangular-shaped trajectories in front of the comet, first at a distance of 100 km and then 50 km.

At the same time, instruments aboard the spacecraft will provide details of the comet’s surface as Rosetta searches for a target site for the Philae probe. Eventually, the orbiter will attempt a close, near-circular orbit at 30 km, and potentially closer, depending on the comet’s activity.

"Arriving at the comet is really only just the beginning of an even bigger adventure, with greater challenges still to come as we learn how to operate in this unchartered environment, start to orbit and, eventually, land," says Sylvain Lodiot, ESA’s Rosetta spacecraft operations manager.

The mission will assess up to five potential landing sites by late August before a primary site is identified in mid-September. By mid-October, ESA will confirm the final timeline for deploying Philae, with a current target of Nov. 1.

"After landing, Rosetta will continue to accompany the comet until its closest approach to the Sun in August 2015 and beyond, watching its behavior from close quarters to give us a unique insight and real-time experience of how a comet works as it hurtles around the Sun," Taylor said.