We are on the comet

Philae has now stabilised on comet 67P/Churyumov-Gerasimenko after landing  not once; not twice but three times. The washing-machine-sized lander is believed to have bounced back up after its initial landing, taking another two hours to land, and then bounced again, taking a further 10 minutes before settling on the surface. Philae is not anchored to the surface as the harpoons designed to keep it in place failed to fire, but it is stable and transmitting data. A decision on whether to refire the harpoons will be made later, as this action could cause the lander to bounce back up off the surface. The news that Philae had successfully landed on the comet was confirmed by Stephen Ulamec, Philae Lander Manager, DLR German Aerospace Centre at approximately 16:10. Harpoons fired, ice screws in, data being received: “We are on the comet,” he said. Following a night of go/no-go decisions, separation of the Philae lander from Rosetta was confirmed at 09:03 GMT, Wednesday 12^th November. It takes the radio signals from the transmitter 28 minutes and 20 seconds to reach Earth, so separation actually occurred in space at 08:35 GMT. There was some cause for concern when, during checks of the lander’s health it was discovered that the active descent system – which provides thrusts to avoid rebound at the moment of touchdown – could not be activated. “The cold gas thruster on top of the lander does not appear to be working so we will have to rely fully on the harpoons at touchdown,” said Ulamec. “We’ll need some luck not to land on a boulder or a steep slope.” There were four go/no-go decisions that began last night at 19:00 GMT, to make sure Rosetta and Philae are prepared for landing. Despite this initial problem, the team decided to push ahead with separation. “There were various problems with the preparation activities overnight but we decided to ‘go’,” said Paolo Ferri, ESA’s head of mission operations. Shortly after separation, the Rosetta orbiter was able to capture a glimpse of Philae using its OSIRIS camera. The lander then took seven hours to reach the comet and the signal was received within a one hour window, opening at 16:02 GMT. Comets are considered to be primitive building blocks of the solar system and may have helped to ‘seed’ Earth with water and perhaps even the organic molecules required for life. On board the Philae lander is the UK-led Ptolemy instrument which will perform on-the-spot analysis of the composition of the ice and organic material within the comet. Rosetta has already been orbiting 67P since August 2014, mapping the comet’s surface; making important measurements of its gravity, mass and shape; assessing its gaseous, dust-laden atmosphere; and probing its plasma environment. “As things stand, the orbiter will continue to shadow the comet until the end of next year. This will be an opportunity to observe how the body responds to its close passage to the sun,” said Professor Ian Wright, principal investigator for the Ptolemy instrument. By Rebecca Dey