Rosetta spacecraft reaches Comet 67P/Churyumov-Gerasimenko

European spacecraft Rosetta became the first ever to catch up with a comet on Wednesday, a landmark stage in a decade-long space mission that scientists hope will help unlock some of the secrets of the solar system.

Scientists and spectators at ESA's mission control in Darmstadt, Germany, cheered Wednesday after the spacecraft successfully completed its final thrust to swing alongside comet 67P/Churyumov-Gerasimenko.

A Twitter account run by the ESA tweeted a photo of the craft's approach shortly after 5:30 a.m. ET.

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The goal of the mission is to orbit 67P at a distance of about 100 kilometers and observe the comet as it hurtles toward the sun. If all goes according to plan, Rosetta will drop the first ever lander onto a comet in November.

Scientists are now on a tight schedule to learn enough about the comet using data from Rosetta to safely do so.

"We know what the comet's shape is. But we haven't really measured its gravity, we don't know yet where the centre of mass is," Rosetta Flight Director Andrea Accomazzo told Reuters ahead of the rendezvous.

We're going to have a ringside seat to see, for the first time, a comet turn into a comet, to develop its tail and explain what for centuries mankind has been puzzled by.- David Southwood, retired Rosetta team member

As it neared 67P/Churyumov-Gerasimenko this year, Rosetta took pictures revealing that the comet is not shaped, as had been assumed, like a rugby or American football, but rather comprises two segments connected by a neck, giving it an asymmetrical shape that has been likened to a duck.

Scientists hope data the probe gathers on the surface of the comet will allow them to peek into a kind of astronomical time capsule that has preserved for millions of years clues about what the world looked like when our solar system was born.

It has taken Rosetta 10 years, five months and four days to reach the comet, a roughly 3-by-5 km rock discovered in 1969. On its way, the spacecraft circled the sun on a widening spiral course, swinging past Earth and Mars to pick up speed and adjust its trajectory.

The mission performs several historical firsts, including the first time a spacecraft orbits a comet rather than just whizzing past to snap some fly-by pictures, and the first time a probe has landed on a comet.

Because the trip is so long and took Rosetta so far from the sun's solar rays, the spacecraft was put in a deep sleep for 31 months and woken up earlier this year.

Comet to grow active

There is little flexibility in Rosetta's schedule this year. The comet is currently between the orbits of Mars and Jupiter. It ishurtling toward the inner Solar System at almost 55,000 km per hour, and the closer it gets to the sun the more active it will become, emitting gases that can make it difficult to predict the trajectory of Rosetta and its probe.

The probe will be thefirst to accompany a comet on its journey toward the sun as its startsto fizz and release the cloud of dust and ice that most people associate with comets.

"We're going to have a ringside seat to see, for the first time, a comet turn into a comet, to develop its tail and explain what for centuries mankind has been puzzled by,"said David Southwood, who oversaw the scientific part of the mission until his recent retirement, in an interview with the Associated Press.

Rosetta blasted off from Earth on March 2, 2004. Since then, it has travelled more than six billion kilometres.The mission will have an estimated cost of 1.3 billion euros ($1.9 billion).

While Rosetta'sPhilaelander will gather data from the comet's surface, plans to bring material extracted from the comet back to Earth were cancelled when NASA pulled out of a joint mission at an early stage. However, the U.S. space agency contributed three of the 21 instruments aboard Rosetta and its Philae lander.

Rosetta is different from NASA's Deep Impact mission, in which a spacecraft fired a projectile into a comet in 2005 so scientists could study the resulting plume of matter. NASA also managed to land a probe on an asteroid in 2001, but comets are much more volatile places because they constantly release dust and gas that can harm a spacecraft.