Pressure around Rosetta due to water outgassing, showing that spacecraft travel for many years in their own gas cloud. Initially, desorption from surfaces is the dominant source, and in this case detected for up to 200 days after launch. Diffusion-sublimation then supports the cloud for years after, with a pedestal from decomposition due to UV- and particle radiation. The outgassing rate appears fairly independent of heliocentric distance. Typical interplanetary pressure is a few 10⁻¹² mbar and below. Figure reproduced from Schläppi et al. (2010).