Why bring a sample back to Earth?

Spacecraft landing with parachute

Imagine holding a piece of a comet in your hand. That’s exactly what the planetary scientists working on CAESAR want to do! While it is possible to send some scientific instruments on a spacecraft like Rosetta to fly next to the comet and make measurements there, it’s just not the same as studying something in labs back here on Earth. Some instruments are just too big, too expensive, or need the sample prepared by a person in a way that is difficult to duplicate using robotics. Even when instruments can be miniaturized, they inevitably sacrifice sensitivity and quality of measurements to do so. By bringing some of the comet back to Earth, we would dramatically increase the science we can do because we could use any and all instruments that we currently have, or will develop in the near future, to understand comets as well as we possibly can.

Comet 67P