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Rosetta and its Comet 67P: Fact file

Comets are considered the primitive building blocks of the Solar System, and most likely helped to 'seed' the Earth with water, and maybe even life. By studying the nature of the comet's dust and gas, Rosetta will help scientists learn more about the role of comets in the evolution of the Solar System.
Rosetta will be the first mission ever to orbit a comet's nucleus and land a probe on its surface.It will also be the first spacecraft to fly alongside a comet as it heads towards the inner Solar System, watching how a frozen comet is transformed by the warmth of the Sun. 

The Rosetta orbiter - spacecraft design
Rosetta resembles a large aluminium box whose dimensions are 2.8 x 2.1 x 2.0 metres. The scientific instruments are mounted on the 'top' of the box - the Payload Support Module - while the subsystems are on the 'base' or Bus Support Module.
The spacecraft entered deep space hibernation in June 2011 and was woken up in January 2014, before rendezvousing with Comet 67P/ Churyumov-Gerasimenko in May 2014. It will follow the comet around the Sun and as it moves back out towards the orbit of Jupiter, till the end of 2015.
Rosetta reached the comet on Aug 6, 2014. It is now circling the comet. It's important to note that Rosetta has not been captured by the gravity of comet 67P (Churyumov-Gerasimenko). It continually needs a series of thruster burns to keep the spacecraft at the comet.
How big is Rosetta's comet? 67P is about 4 km wide. In contrast, Rosetta's most visible features are its solar arrays that span 32 m.
The first measurement reveals a temperature of -70 degrees C, suggesting that the surface of comet 67P is mostly covered by dust. It's clearly not just a ball of ice.
Rosetta's scientific imaging system OSIRIS has photographed 67P from up close and shows stunning images taken from a distance of about 12,000 km. This showed that the nucleus of the comet comprises two distinct segments joined by a 'neck', giving it a duck-like appearance.
In the images, scientists are able to identify geological features like cliffs and crags, evidence of past landslides, as well as a multi-variable terrain and surface composition.
Rosetta then took photos from about 100 km distance: the high-resolution images of the surface, measurements of the comet's surface temperature, and the pressure and density of gas around the nucleus together have told us more about the comet. In addition, measurements of the comet's orientation with respect to the Sun, its rotation, mass and surface gravity have been determined.
All of these factors will be used to decide the location on the comet
where the lander Philae will land and directly study the comet, and even
its rocks below the surface. So far, 5 possible landing sites (out of an
initial 10, numbered from A to J) have been identified. Sites (B, I and J) are located on the smaller of the two lobes of the comet and two sites (A and C) are located on the larger lobe. 
Until its release, the 100kg Philae lander is carried on the opposite side of the orbiter to the large high-gain antenna dish. As Philae touches down on the comet, two harpoons will anchor it to the surface; the self-adjusting landing gear will ensure that it stays upright, even on a slope, and then the lander's feet will drill into the ground to secure it to the comet's surface in the low gravity environment. Philae carries 9 scientific instruments, including a drill to sample subsurface material. At that time, we will know more about comets and their composition than we've ever known.