Researchers with the European Space Agency’s (ESA) Rosetta mission believe that they have found the site where they will attempt to deposit the Rosetta spacecrafts Philae lander. It would be wrong to say that it is an ideal site. On the volatile world of the two and a half mile wide Comet 67P/Churyumov-Gerasimenko there are no ‘ideal’ sites. However, the region dubbed “Site J” appears to offer the best available location for a successful landing.

Site J is located on the head of the irregularly shaped comet and on or about November 11, scientists will attempt to deposit a 220 kg lander on the spot.

“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. None of the candidate landing sites met all of the operational criteria at the 100% level, but Site J is clearly the best solution.” says Stephan Ulamec, Philae Lander Manager at the DLR German Aerospace Center, in a statement.

The process of choosing a landing site began almost immediately after Rosetta arrived at the comet on August 6. By August 24 scientists had narrowed their search to five candidate sites. Since that date, as Rosetta moved closer to the comet researchers have gathered better photography and additional data on the potential landing sites.

Over the last few days a variety of scientists and engineers from Philae’s Science, Operations and Navigation Centre at France’s CNES space agency, the Lander Control Centre at DLR and others representing the Philae Lander instruments and ESA’s Rosetta team met at Toulouse, France to make a decision.

In order for a site to be viable, the team had to be able to identify a safe trajectory for landing Philae and the site had to have a minimum of visible hazards. The site also had to have an optimal number of daylight hours so that the lander could recharge and not rely solely on battery power. The number of clear communications passes with the orbiter was another important factor.

Site J had the smoothest surface, with most slopes at less than 30 degrees to the local vertical and relatively few holders. It also had sufficient sunlight to recharge Philae, which allows for greater opportunities for experiments. The descent from Rosetta to the comets surface at the selected site will take approximately 7 hours, which means a minimum of drain on the landers battery.

Next a highly detailed operational plan will be prepared before the landing is attempted in mid-November. Once the lander is deployed the descent will be autonomous using pre-programmed commands. Once it touches down, Philae will use harpoons and ice screws to attach itself to the surface of the comet and take a 360 degree panoramic photo so that the research team knows exactly where it has landed.

If all of these steps are successful, ESA scientists will be able to get the best measurements to date of the surface of a comet, including temperature, environmental and core samples.

“No one has ever attempted to land on a comet before, so it is a real challenge. The complicated ‘double’ structure of the comet has had a considerable impact on the overall risks related to landing, but they are risks worth taking to have the chance of making the first ever soft landing on a comet,” says Fred Jansen, ESA Rosetta mission manager.

The landing date will be confirmed, after further analysis, on September 26. An alternative location “Site C” is available if there are unexpected problems with the primary Site J. Additional information on the Rosetta mission is available on the ESA’s website.