Rosetta's mission, if executed successfully, could give scientists an unprecedented look at how comets work. These "dirty snowballs" are the most primitive bodies in the solar system. They contain the original material left behind when a cloud of dust and gas collapsed to form the planetary system some 4.6 billion years ago. When Rosetta's lander, Philae, touches down, it could collect information to help solve many unknowns such as:
Comets are believed to contain organic molecules, nucleic acids (the building blocks of DNA and RNA), and amino acids (the building blocks of proteins). All are essential ingredients for the beginning of life on Earth but did they arrive on this planet via a comet?
Advances in science have improved our ability to track asteroids and comets that come close to Earth's orbit. However, our ability to blow a threatening one up out in space depends on having a better understanding about what they are made of.
About 71 percent of our planet is covered in water, and it has been long believed to have come from comets that pounded early Earth. Recent studies have questioned that theory, however. Rosetta could provide a more definitive answer.
Comet 67P/Churyumov-Gerasimenko orbits the sun every 6.6 years. It is a short-orbit comet, meaning it circles the sun in less than 200 years. Scientists believe it is one of 12 billion comets from the Kuiper belt, a repository of comets just outside of Neptune's orbit, but that it has since escaped the Kuiper belt to travel within the inner solar system.
Is the comet big enough to threaten Earth? Maybe. Movies make humans worry about comets striking Earth. Scientists have that on their minds, too they just also map out ways to avoid a collision.
How long does it take to communicate with the rover? Since the comet is 3.7 billion miles away, communication between Rosetta and controllers takes 28 minutes and 20 seconds each way.
How fast is the comet traveling? The comet is traveling 83,885 miles-per-hour. At that speed, it would take only 18 minutes to circle the Earth.
The Rosetta rover used Earth and Mars to build up speed. As it slung itself near the orbits of those planets, it passed other comets on its approach to Comet 67P/Churyumov-Gerasimenko. It then executed maneuvers allowing it to begin orbiting the comet, which itself is circling the sun at 83,885 miles per hour. Rosetta will travel alongside the comet for three years, collecting data.
March 4, 2005 1. Orbiter Rosetta launched
March 4, 2005 2. First Earth flyby
Feb. 25, 2007 3. Mars flyby
Nov. 13, 2007 4. Second Earth flyby
Sept. 5, 2008 5. Asteroid Steins flyby
Nov. 13, 2009 6. Third Earth flyby
July 10, 2010 7. Asteroid Lutetia flyby
June 8, 2011 8. Enters deep-space hibernation
Jan. 20, 2014 9. Ends hibernation
May-Aug., 2014 10. Comet rendezvous maneuvers
Aug. 6, 2014 11. Arrival at Comet 67P/Churyumov-Gerasimenko
Nov. 12, 2014 12. Philae landing
Aug. 13, 2015 13. Comet closest to sun
Dec. 31, 2015 14. Mission ends
1. About 14 miles above the surface of the comet, Rosetta will provide a precise, well-timed push to move the Philae rover out of its holding bay.
2. Philae will begin to take photographs and measurements of the environment as it descends, a journey that is expected to take seven hours.
3. With surface gravity several hundred thousand times weaker than on Earth, Philae needs to touch down at a pace no faster than walking.
4. On touchdown, the rover will shoot an anchor into the surface to keep it from bouncing back into space. Foot screws will then drill into the surface to secure the rover.
Though the best landing site was selected, the chosen surface may not be perfectly flat. It could also be boulder-ridden or too hard or soft for the foot screws and harpoon to secure the lander. A safe landing alone will be a major accomplishment.
But once the rover has landed, a panoramic photo will be taken. Then a sequence of scientific experiments from 10 separate instruments will begin. They are expected to take nearly 60 hours.
The composition of the comet's surface and subsurface will be among the things analyzed. Plus, since the lander rides on the comet, scientists should be able to tell how the body changes from day to night, especially what happens as it approaches the sun.