Rosetta target comet 67P/Churyumov-Gerasimenko -: Postperihelion gas and dust production rates

The evolution of the activity and composition of the coma of ROSETTA target comet 67P/Churyumov-Gerasimenko was studied along its postperihelion orbit from 2.29 AU to 3.22 AU. The comet had a major drop of activity between 2.5 AU and 2.9 AU, which manifested most obviously in its light curve (the brightness decreased by 3 mag), but is also confirmed by the production rates derived from spectrophotometric measurements. The strong decrease of activity indicates a change in the outgassing behaviour of the nucleus and might be due to water sublimation becoming less efficient. The spectrophotometric measurements at 2.9 AU show that the coma is at least slightly depleted in C-2 with respect to CN.