European probe on course for a landing on a comet

BERLIN - It's been likened to a parachutist trying to land on a mountaintop. Or a person attempting to leap from one speeding car to another.

The European Space Agency is planning to land an unmanned spacecraft on a comet next year in an unprecedented and exquisitely tricky mission that has been underway for almost a decade and is about to enter a critical new phase.

The agency announced Tuesday that its Rosetta probe, which has been journeying through space since its launch in 2004, will be awakened from hibernation next month and will aim to drop a lander onto the icy surface of comet 67P/Churyumov-Gerasimenko on Nov. 11, 2014.

The plan is different from NASA's Deep Impact mission, which used a probe to fire a projectile into a comet in 2005 and create a plume of matter for scientists to study. That was just a drive-by compared with the rendezvous the Europeans are planning.

Scientists hope that by flying Rosetta alongside the comet and sending down a barrel-size lander to collect and analyze samples, they will get an even better idea of what comets are made of and what role they played in the formation of our solar system.

"Nobody has ever done this before," said Paolo Ferri, head of mission operations at the European Space Agency.

Ferri noted that while NASA managed to land a probe on an asteroid in 2001, comets are much more volatile places because they constantly release dust and gas that can harm a spacecraft. A comet is essentially a dirty snowball; an asteroid is a rock.

To catch 67P as it orbits the sun at up to 62,000 m.p.h., Rosetta has made several fly-bys of Earth, Mars and the sun, using their gravity to accelerate.

Once the spacecraft picked up sufficient speed and was on course to rendezvous with the comet, ESA put Rosetta into hibernation for more than two years to conserve energy.

This also gave engineers the time to find workarounds for two glitches that threatened the mission: a problem with two of the four reaction wheels used to turn the spacecraft, and a small helium leak that could affect the thrusters vital for its final maneuvers.