Landing on a comet is hard: Rosetta searches for the sweet spot

The Rosetta mission has narrowed down the selection of possible landing sites to just five candidates, but it's going to be tricky to touch down.

Rosetta landing sites
Four potential landing sites are marked in this image.Photo by ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM

The Rosetta spacecraft made a historic rendezvous with comet 67P/Churyumov-Gerasimenko earlier this month after a 10-year chase. It was a cause for celebration, but there's more work to come. Now that Rosetta is in orbit around the comet, the European Space Agency has to decide where to place the spacecraft's lander on the flying space object's surface.

The comet is composed of ice and rock. The Philae lander will need to land safely and then drill into the comet's surface to anchor itself in place, a trick that will be kind of like trying to cling to that rolling Indiana Jones boulder with your fingernails. The ESA first identified 10 possible landing sites, but has since narrowed that down to five.

"This is the first time landing sites on a comet have been considered. The candidate sites that we want to follow up for further analysis are thought to be technically feasible on the basis of a preliminary analysis of flight dynamics and other key issues - for example, they all provide at least six hours of daylight per comet rotation and offer some flat terrain. Of course, every site has the potential for unique scientific discoveries," says Stephan Ulamec, Philae Lander Manager at the German Aerospace Center.

Each potential landing area covers six-tenths of a square mile, making it hard to pinpoint an exact spot where Philae could touch down. The Rosetta team is looking to avoid large boulders and other landscape hazards while making sure the lander gets enough sunlight to recharge its batteries.

The ESA has a few more weeks to work out the best landing site before committing to a location. Rosetta is in the process of moving closer to the comet, which should help with the analysis. Philae is scheduled to land in mid-November. If all goes well, the lander will take detailed images of the comet's surface and work to determine the composition of the comet itself. Rosetta will be tracking changes to the comet as it moves past the sun and is exposed to increasing solar radiation.

The Rosetta mission represents a lot of firsts for human-led exploration of space. Rosetta is the first spacecraft to go into orbit around a comet. It will be the first to place a lander on one and the first to take images from the surface of a comet. Scientists hope we will learn a lot about the composition of comets and perhaps even peek into the origin of our solar system. That's a lot riding on finding one good landing site.

Rosetta lander sites
Another side of the comet with possible landing sites marked.Photo by ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM