To understand the sample we would bring back, we would need to have a lot of information about where it came from. There have been ten successful missions to seven different comets, and one important thing we’ve learned is that each comet is unique. Comet 67P has already been thoroughly studied by the Rosetta spacecraft with all its science instruments and its Philae lander. Choosing this comet as CAESAR’s target means we only need cameras for navigating, picking a sample site, and documenting the sample collection, along with the robotics for collecting the sample and the capsule in which to store the sample. All the science can be done back here on Earth. This allows us to devote precious resources to acquiring and preserving the most scientifically valuable sample possible.
Comet 67P is also conveniently located, close enough to reach with a spacecraft, but far enough away and new enough to the inner solar system that it has not been as chemically altered by close passes with the Sun as some other comets.