  Here we review some of the major findings of the mass spectrometer suite
ROSINA on board of ESA's Rosetta spacecraft to comet 67P/Churyumov-Gerasimenko.
For more than 2 years, ROSINA continuously measured the composition of the
gases sublimating from the comet's nucleus. ROSINA measurements provided
insight into the origin of the ices in 67P/Churyumov-Gerasimenko. The obtained
molecular, elemental, and isotope abundances revealed a composition more
complex than previously known. Furthermore, a subset of these measurements
indicate that a substantial fraction of the molecules incorporated into the
comet predate the formation of the solar system.
