Free Astronomy Magazine September-October 2014

SMALL BODIES and asteroids). Accurately determining the chemical-physical properties of comets is consequently the only way to understand the composition and the initial conditions of the protosolar cloud and its subsequent evolution inside the system hosting us. It is thus precisely for its significant role in revealing the “vocabulary” of an otherwise dark era, that to the probe has been given the name of the ancient city on the Nile delta where the eponymous stone that al- lowed the deciphering of hieroglyphs was discovered. Similarly, to the lander was given the name of the Egyptian place where in 1815 was discovered an obelisk with hiero- glyphic inscriptions translated into ancient Greek, which turned out to be fundamen- tal for correctly interpreting the more fa- T wo images of 67P/Churyu- mov-Gerasimenko taken in the vicin- ity of the rendez- vous: the first on 5 August from 145 km away and the second on 6 August from 96 km away. [ESA/ Rosetta/NAVCAM] The diagram on the side summa- rizes an observa- tion made with the VIRTIS instru- ment (Visible and InfraRed Thermal Imaging Spectro- meter), thanks to which it has been possible to deter- mine that the sur- face temperature of the cometary nucleus is minus 70°C –a value higher than ex- pected of about 20-30°C, which in- dicates a predomi- nance of dust and lack of ice. [ESA]