ESA’s Rosetta mission needs to deliver its lander, Philae, to a site in the southern hemisphere of comet 67P/Churyumov-Gerasimenko, according to a new study of the comet’s nucleus.

“Southern sites appear to be both the safest and the most scientifically interesting,” said Jeremie Lasue, who presented the findings at the European Planetary Science Congress in Rome 23/9

“Churyumov-Gerasimenko is a time capsule holding material from the birth of the Solar System. The nucleus’s southern hemisphere has been heavily eroded, so Philae will not have to drill down far to find those pristine samples. At the time of Rosetta’s rendezvous, gas will be escaping mainly from the northern hemisphere, so it will be safer for Philae to touch down in the south. In addition due to the orientation of the comet, the southern hemisphere will be protected from extreme temperature variations at the time of delivery,” said Lasue.

After a ten-year chase, Rosetta is due to begin maneuvers to rendezvous with comet Churyumov-Gerasimenko in May 2014 and go into orbit around the nucleus in August. Philae is scheduled to drop down onto the surface of the nucleus in November. The orbiter and lander will then monitor the comet’s evolution over the next 13 months as it approaches the Sun and then travels away again.

Lasue and colleagues from the INAF-IASF and IFSI institutes in Rome have developed three-dimensional computer models that predict the activity of Churyumov-Gerasimenko’s nucleus from the first few months of Rosetta’s initial encounter until the comet’s closest approach in August 2015. Comet nuclei are a porous mixture of dust, ice and frozen gases such as carbon dioxide and carbon monoxide. As the nucleus approaches the Sun and starts to heat up, the gases vaporize and the tail, or coma, starts to form.

The models predict how heat is transferred through the layered nucleus and the vaporization rates of the ices as the comet approaches the Sun. Churyumov-Gerasimenko’s lumpy, diamond-shaped nucleus is tilted at an angle of 45^o, which means that the south pole is directly exposed to the Sun at the closest approach. The simulations show that after several orbits close to the Sun, the south pole has been significantly more eroded than the north, potentially giving Philae easy access to pristine cometary material just below the surface. Philae will be able to drill down up to 30cm to collect samples of the cometary soil for on-board analysis.

Source: IFSI Institute