On November 12, the European Space Agency (ESA) made history when it successfully landed a robotic space probe on a comet nucleus.
After a ten-year journey through space, the Philae lander attached to its companion spacecraft, Rosetta, and finally reached its target: Comet 67P/Churyumov-Gerasimenko. At this point, Philae detached from the side of Rosetta and began its descent to the surface, while Rosetta continued orbiting the comet.
The mission was carefully planned; several gravity assists by Earth and Mars were used to ‘slingshot’ Rosetta (with the Philae lander attached) into deep space, along a trajectory that would dodge asteroids and precisely meet up with the three-mile-wide target.
After all of this planning, Philae nearly bounced right off 67P. Some of the mechanisms designed to secure the lander to the surface failed, namely an anchoring harpoon and a downward thruster. The comet has very weak gravity and an extremely low escape speed, meaning a small bump could send Philae floating into space.
Scientists at the ESA discovered that Philae actually landed three times, bouncing twice after its initial touchdown. The first bounce was half a mile high, and after bouncing a second time, Philae came to rest against the base of a small cliff, far from its intended landing site. This would later become a problem.
Philae contains numerous scientific instruments designed to determine what comets are made of, how they form, and how they react to the sun’s radiation. Rosetta’s job is to photograph the comet in its different stages and to transmit data back to earth.
The data collected by Rosetta and Philae could answer many questions about the composition and origin of comets, and even help us understand comets’ role in the formation of our solar system. One theory states that most of Earth’s water came from comets that collided with it in its early stages, and that these comets may have contained organic molecules that gave rise to life on Earth. If this is true, the study of comets may help answer one of the big questions of astronomy, “Are we alone?”
Unfortunately, Earth won’t be hearing from Philae again for a while—possibly ever. Situated in the shadow of a cliff, the lander is currently receiving an hour and a half of sunlight every 12-hour comet day, which does not provide enough power via solar panels to keep it up and running. This may change as the comet approaches the sun, but experts are unsure. The lander did manage to collect and transmit some data while is battery power diminished, including the first ever close-up pictures of a comet nucleus.
Rosetta continues to observe 67P from about a three-mile radius orbit, sending back data for scientists to analyze.