How Did They Decide Which Comet To Land On?

Being the curious person that I am, how did scientists decide which comet to land on?  Why did they choose the one they did so far away with all the risk that came with it?  What good can come from it?  Who pays for all of this stuff anyway?

"Then there was more waiting, with amusing updates via the Twitter accounts of Rosetta and Philae. “Finally! I’m stretching my legs after more than 10 years. Landing gear deployed!” read a Twitter posting from Philae.

The web comic XKCD also provided real-time updates, even mentioning the problem with the nitrogen thruster. In the comic, Rosetta told Philae that mission control was worried about the thruster, and the lander responded, “I really hope harpoons work on comets.”

The harpoons turned out to be a valid concern.

“There are some indications that they might not have been fired, which could mean that we are sitting in soft material and we are not anchored,” Dr. Ulamec said. “We have to analyze what is the actual situation.”

The XKCD comic updated: “Do harpoons work on comets? Don’t know.”

For now, Philae is working, and the instruments have already sent back some images and data. But if it is not anchored, Philae may not operate as long as hoped — the original goal was next March — as emissions of dust and gas grow as the comet moves nearer to the sun.

Even if the lander cannot complete the full mission, managers have said, Rosetta will still be a resounding success. Planetary scientists have never looked at a comet so close up for so long.

Comets are frozen leftovers from the formation of the solar system. Rosetta is named after the Rosetta Stone, the engraved block that was crucial in deciphering Egyptian hieroglyphics, and scientists hope the spacecraft’s observations will offer important clues to how the solar system came together 4.5 billion years ago. (Philae was an island, now submerged in Lake Nasser, where an obelisk provided clues to solving the Rosetta Stone.)

Previous missions have zoomed by comets at high speeds, providing only brief examinations. By contrast, Rosetta will be a constant companion as Comet 67P approaches the sun, swings around and heads out again, its instruments potentially providing more than two years of data."

As you can see there are a lot of unaswered questions.  I would like to know more about the mission since it has been such a long time in planning.

Ed