The European Space Agency’s Rosetta mission to land a probe on a comet was successful on Nov. 12.

The Rosetta mission began its planning 25 years ago and launched March 2, 2004. The 4 billion-mile journey took 10 years to reach the comet.

The probe named Philae took seven hours to descend to the surface of Comet 67P/Churyumov-Gerasimenko that was traveling at 40,000 mph through space. The comet’s mass is about 10 billion tons and in the shape of a rubber duck.

The landing site, named Agilkia, was chosen after six weeks of images and data collected by Rosetta. During the final health checks on the lander, researchers detected a problem with the small thruster on top that was designed to help counteract the recoil of the harpoons and to push the lander down onto the surface of the comet. Because Philae’s third foot is not lowered to the surface, it is impossible for the researchers to use the lander’s drill.

One of the key objectives of the mission was to drill for sub-surface material for chemical analysis using the onboard labs.  Controllers are looking into what they can do to lower the third foot to the surface of the comet. If they are not able to lower the foot, the drilling may be pushed till the end of the lander’s battery life.