In an interview he gave us a few months ago, Sylvain Lodiot, Rosetta Spacecraft Operations Manager at ESA, suggested that were the Rosetta mission to be extended beyond next December, it might be worth attempting to land the orbiter on the nucleus of comet 67P/Churyumov-Gerasimenko. This idea would appear to have gained ground, since ESA’s Scientific Programmes Committee recently confirmed a 9-month extension and announced this end-of-mission scenario is being seriously considered.
Simply because less sunlight will be available for the orbiter’s huge solar arrays after perihelion on 13 August, when the comet and its man-made escort will start receding from the Sun. By September 2016, there will no longer be sufficient energy to power Rosetta and its science instruments properly.
The extension will enable mission scientists to monitor the decline in the comet’s activity for a longer period and instruments will have multiple opportunities to compare ‘before- and after-perihelion’ data, which will give us a much better idea of how comets behave as they get closer to the Sun. The scientists will also be able to take advantage of flybys at much lower altitudes, when there may be an opportunity to make a definitive visual identification of Philae on the comet’s small ‘lobe’.
Slow descending spiral
According to current estimates and taking into account the orbiter’s planned flight trajectories in the months ahead, it has enough propellant left to manoeuvre freely until September 2016, but not to go into hibernation again and resume operations when the comet approaches the Sun at its next perihelion in January 2022.
Mission planners are therefore looking at the idea of attempting to set Rosetta down on the comet’s nucleus. Although it was designed for precisely that purpose, Philae’s own extraordinary landing shows that such an end-of-mission scenario would be far from plain sailing and that all radio contact with Earth would be lost. But the approach phase, most likely a slow spiralling descent over several months, would afford unprecedented viewing opportunities and provide a fantastic finale rather than simply shutting down communications and leaving Rosetta to drift off into the outer reaches of the solar system. Obviously, the extension of the Rosetta mission and its hypothetical landing are both predicated on the orbiter’s health status after it passes perihelion in August, when it will be subjected to intense activity from the comet’s nucleus.
Rosetta is an ESA mission with contributions from its member states and NASA. Rosetta's Philae lander is provided by a consortium led by DLR, the German Aerospace Centre, the Max Planck Institute for Solar System Research (MPS), CNES and ASI, the Italian space agency. Rosetta is the first mission in history to orbit a comet, escort it on its course around the Sun and deploy a lander on its surface.