Ptolemy - a GCMS to measure the chemical and stable isotopic composition of a comet

Comets have captured the imagination for as long as man-kind has looked up to the heavens. The successful launch of the Rosetta mission, in March 2004, means that for the first time in situ analyses of the chemical and isotopic composition of a cometary nucleus are now a distinct possibility. Ptolemy, on board the Philae Lander, is a complete instrument package designed for the analysis of cometary volatiles, refractory organic materials and silicates. Using the MODULUS protocol, the objectives of Ptolemy are to provide a complete description of the nature and distribution of light elements (H, C, N and O) present in the nucleus of the comet, as well as determining their stable isotopic compositions. Ptolemy also aims to provide ground-truth measurements of those volatiles that are subsequently detected further out from the nucleus in the coma. Along with the other instruments the aim is to unlock some of the secrets of the early Solar System trapped within the comet and to answer fundamental questions about the origins of water and even life on Earth. This paper describes the fundamental principles of Modulus and the primary components of Ptolemy