Rosetta mission Š comet landing site to be unveiled The European Space Agency will reveal on September 15 which of five possible sites it has chosen for the touchdown of the Rosetta spacecraftÕs Philae lander on 67P/Churyumov-Gerasimenko. The first-ever landing by a spacecraft on a comet is due to take place on November 11 Nov 11, Touchdown: Philae probe released Jan 20, 2014: Rosetta woken from hibernation Aug 2015: Closest approach to Sun Aug 6, Rendezvous: Rosetta maps comet to find suitable site to dispatch lander Mar 2004: Rosetta launched Mars orbit Earth orbit June 2011: After four flybys of Earth and Mars, Rosetta is put into hibernation to save energy Dec 2015: Nominal end of mission Comet 67P/C-G orbit ------------------------------------- Rosetta orbiter Instruments measure structure of nucleus, dust and plasma tails. Others for visible, ultraviolet and infra-red imaging ------------------------------------- How to land on a comet Ejection: Once Orbiter is aligned correctly, at around 10km above cometÕs surface, ground station will command fridge-sized lander to self-eject from mother ship and unfold legs Descent: Philae will ŅfallÓ at about 1m per second Š due to cometÕs weak gravitational pull. Descent, expected to take 8-12 hours, can not be controlled from Earth due to immense distance Touchdown: Two harpoons prevent craft bouncing back into space ------------------------------------- ------------------------------------- Potential sites If one considers comet to look like rubber duck, three sites (B, I and J) are on head; two are on body (A and C) 67P/Churyumov-Gerasimenko Named after Klim Churyumov and Svetlana Gerasimenko, who discovered it in 1969 Icy core is around 4km(2.5 miles) wide Takes 6.5 years to orbit Sun ------------------------------------- Landing site requirements Must be relatively flat and free from boulders and fissures Needs right amount of sunlight Š enough to recharge landerÕs batteries but not so much as to cause overheating Must offer greatest potential, such as proximity to one of jets of gas and dust that blast out of cometÕs surface ------------------------------------- Philae lander Experiments: X-ray spectrometer measures elemental composition of cometÕs surface; radiowaves probe internal structure of nucleus; six micro-cameras take panoramic pictures Gas analysers identify complex organic molecules and isotopic ratios of light elements Weight: 100kg Harpoons: Fired on landing to anchor probe to ground. Sensors measure density and thermal properties of surface Feet: Ice screws help secure craft to surface Legs: Absorb kinetic energy to reduce risk of bouncing. Can rotate or tilt to return lander to upright position Sampling system: Can drill 25cm into surface. Samples deposited in ovens or delivered for microscope inspection Sources: European Space Agency, The Planetary Society Pictures: ESA/Rosetta/NAVCAM, ESA/Rosetta/MPS for OSIRIS Team