The Rosetta spacecraft has finally made contact with comet 67P/Churyumov-Gerasimenko. Astronomers already had previous ideas of what they are likely to find, but experts worldwide are excited about finally getting a closer look at a comet.
Rosetta was launched to the comet on Mar. 2, 2004, and has traveled roughly four billion miles since that time. By Aug. 4, 2014, the spacecraft closed within 145 miles of the comet, closer than the International Space Station orbits above the Earth. From this distance, the observatory snapped one of the most dramatic photographs ever taken of one of these visitors from the distant solar system.
Comets can be thought of as "dirty snowballs" in many ways - they are composed of water ice, frozen carbon dioxide (dry ice), ammonia, and dust. As these materials heat as the comet heads toward the Sun, they can form one or more tails, providing comets with their distinctive look.
Comet Churyumov-Gerasimenko was discovered on Sept. 20, 1969, by Klim Churyumov, who was conducting a survey of comets. This comet orbits close to the plane in which the planets of the solar system orbit.
When mission planners for Rosetta were looking for a target, they needed a body that came close to the ecliptic plane on which the planets move, to minimize cost and mission duration. They also wanted an active comet, which had been well-studied from the ground, and was known as an active body. Finally, the comet needed to approach the inner solar system during the proposed time line of the Rosetta project. They selected comet 46P/Wirtanen as the target for the craft. After a launch delay forced the mission to miss that opportunity, a decision was made to visit 67P/Churyumov-Gerasimenko instead.
Comet 67P/Churyumov-Gerasimenko has a nucleus that is less dense than water, suggesting the body itself may be porous. This body is pitch-black, suggesting a layer of carbon or organic materials could be covering the surface of the tiny body.
"Orbit entry will take place on 6 August, and will be triggered by a small but crucial thruster firing lasting just 6 min 26 sec," Rosetta mission planners wrote in a press release.
The Philae probe will land on the comet, carrying nine instruments, as part of an effort to better understand the icy visitor.
CONSERT (COmet Nucleus Sounding Experiment by Radiowave Transmission), a radar attached to Philae, will allow astronomers to "see" beneath the surface of the comet, examining underlying structure.
COSAC (The COmetary SAmpling and Composition) is capable of conducting analysis of the organic materials which could cover the surface of the celestial body.
Rosetta has begun examining the comet using an ultraviolet imaging spectrograph called ALICE. This tool could reveal the temperature at which the comet formed. The craft will also provide a range of cameras with which to observe the celestial artifact from the ancient solar system.
The European Space Agency produced and released a computer visualization of how Rosetta will obtain a low, regular path around the comet.
