Site J it is! European Space Agency scientists have selected a safe but intriguing region on 67P/Churyumov-Gerasimenko for humanity’s first-ever soft landing on a comet. Site C, located on the larger ‘body’ of the comet, was selected as backup.
Choosing a landing site hasn’t been easy. Safety was a prime concern. Site J appears to have relatively few boulders and receives sufficient daily sunlight to recharge Philae and continue science operations on the surface beyond the initial battery-powered phase. The majority of slopes there are sloped less than 30º relative to the local vertical, reducing the chances of Philae toppling over during touchdown. The J Site also allows the probe to be in regular communication with the orbiter as it passes overhead during each orbit of the comet.
“As we have seen from recent close-up images, the comet is a beautiful but dramatic world – it is scientifically exciting, but its shape makes it operationally challenging,” says Stephan Ulamec, Philae Lander Manager at the DLR German Aerospace Center.
Since the descent to the comet is passive in the comet’s low gravity field – like dropping a piece of paper – it’s only possible to predict the landing point to within about 1,000 feet (~300 meters). Descent time to the surface is estimated at 7 hours. Landing has to happen by November before 67P/C-G becomes too active spewing dust and gas as it draws ever nearer the sun.
“There’s no time to lose, but now that we’re closer to the comet, continued science and mapping operations will help us improve the analysis of the primary and backup landing sites,” says ESA Rosetta flight director Andrea Accomazzo.
Site J offers scientists a place to analyze 67P/C-G’s ice and dust and study the ice vaporization processes that make comets such special critters.
During the descent, Philae will take photos and observe the comet’s dusty-gassy environment. Once it gently drops to the surface at the equivalent of a walking pace, it will fix itself to the comet’s crust using a harpoon-like device and ice screws in the landing legs. It will then shoot a 360-degree panorama of its surroundings.
Next comes an analysis of the plasma and magnetic environment, and the surface and subsurface temperature. The lander will employ a drill to collect samples from beneath the surface and analyze them inside its onboard lab. The interior structure of the comet will also be explored by sending radio waves through the surface towards Rosetta.