Rosetta: How comet particles are analysed With the Rosetta spacecraft in orbit around comet 67P/Churyumov-Gerasimenko, scientists are hoping for a windfall of new information about these strangest of objects. Previous research established that comets are a mix of ice and rock, and one theory is that they may have delivered water and carbon to the early Earth. A Nasa mission called Stardust collected particles from a comet in 2004. Science editor David Shukman reports from one of the laboratories that have been analysing the samples, the Diamond Light Source near Oxford.