Free Astronomy Magazine September-October 2014

15 SEPTEMBER-OCTOBER 2014 SMALL BODIES must not have exceeded 3 metres per second (a mech- anism of this type is believed to be behind the forma- tion of the asteroid 25143 Itokawa). An alternative hypothesis suggests that in the past the form of the nucleus was much more regular and that it has assumed its present shape only as a result of evap- oration of large amounts of ice. It is likely that the ideas will become clearer once Rosetta will determine the composition and density of the two blocks. For now, the only certain thing is that the unusual mass (and hence gravity) distribution will result in some extra dif- ficulties both in inserting Rosetta into a stable orbit and in the procedure for the descent of Philae on the com- et. On 1 August, with the probe at only about 1000 km A picture shot on 10 August from a distance of 110 km, similar to the previous one, but with a different camera and sunlight incidence angle. [ESA/Rosetta/NAVCAM] In the video below, the complex tra- jectory of Rosetta around the comet, before entering into a stable orbit. [ESA-C. Carreau]