Free Astronomy Magazine September-October 2014

SMALL BODIES was not uneventful. In fact, in de- signing its complex trajectory the ESA engineers made sure that the probe did “fly over” the sur- faces of two asteroids never be- fore closely observed. The two flybys involved 2867 Šteins, “skimmed” at a mere distance of about 800 km on 5 September 2008, and 21 Lutetia, crossed over by the probe on 10 July 2010 at a closest distance of 3170 km. Almost a year after this last space encounter, Rosetta was put on standby, to then be reactivated, as aforesaid, last January. Before commenting on the most interesting part of the mission, it may be useful to briefly mention the reasons that led to its actuali- zation, the type of in- struments available on board the probe and the objectives that as- tronomers and techni- cians expect to achieve through them. The idea of sending a probe to orbit around a comet is undeniably dated and goes back to the late ’70s. It is though only in 1993 that the project for the Rosetta mission is ap- proved as part of the ESA programme, thanks also to the success of the pioneering Giotto mission which, in 1986, brought for the first time a probe to closely flyby the active nucle- us of the most famous comet of all, 1P/Halley. More than 10 years after the project appro- val Rosetta was finally launched, and then an- I n the video, the comet's rotation as it appeared on 28 June and 14 July. Just below, an image taken on 29 July from 1950 km away, which already clearly shows the odd shape of the nucleus, even more defined in the bottom pic- ture taken on 1 August from a distance of 1000 km. [ESA/Roset- ta/MPS for OSIRIS Team MPS/UPD/ LAM/IAA/SSO/INT A/UPM/DASP/IDA]