Landing spot chosen for historic soft landing attempt on comet

By Ted Bonnitt on September 17th, 2014
Landing spot chosen for historic soft landing attempt on comet
Photo of comet showing the location of the primary landing site for Rosetta’s lander Philae. Photo credit: ESA
Photo of comet showing the location of the primary landing site for Rosetta’s lander Philae. Photo credit: ESA

Scientists have picked their parking spot on Comet 67P/Churyumov–Gerasimenko for the Rosetta mission lander Philae.  

The spot, known as “Site J” is located on the head of the comet and was chosen for it’s science potential and for posing a minimum risk for the landing craft.

The landing is planned for November 11. If successful, the lander will then take measurements and conduct the first-ever study of “the composition, structure and evolution of a comet,” according to Jean-Pierre Bibring, a lead lander scientist and principal investigator for the mission in Orsay, France.

“Site J in particular offers us the chance to analyze pristine material, characterize the properties of the nucleus, and study the processes that drive its activity.”

The landing site search began in earnest once the Rosetta craft arrived at the comet on August 6, 2014, after a 10 year journey from Earth that sent it in sling shot fashion around the gravitational pull of numerous planets to its rendezvous with the comet. The spacecraft has been orbiting the comet since its arrival and is now less than 20 miles away from the surface, allowing scientists to get a close look at potential landing sites for the landing craft Philae.

No easy landing

“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.

Mission planners need a landing site that is well illuminated with a good balance of day and night hours and free of large rocks and boulders. It also has be a place that will allow frequent communication with the Rosetta orbiter.

The descent to the surface of the comet will take about 7 hours, which was another deciding factor in choosing the landing site, in order to preserve as much battery power as possible on the lander. Although none of candidate sites fit all the criteria, Site J was the best of the bunch. A back up landing site has also been identified.

Touchdown is risky

The landing is full of risks, considering that the comet is just a two and half mile wide, moving target and mission planners will have to set autonomous landing instructions on the lander’s computer due to the great distances involved from Earth.

“Of course, we cannot predict the activity of the comet between now and landing, and on landing day itself. A sudden increase in activity could affect the position of Rosetta in its orbit at the moment of deployment and in turn the exact location where Philae will land, and that’s what makes this a risky operation,” said ESA Rosetta flight director Andrea Accomazzo.

The lander will take photographs as it descends and slows to a landing at the speed of a person’s walking pace. After touchdown, the lander will use harpoons and ice screws to anchor itself to the surface. It will then make a 360° panoramic image of the landing site to help determine where and in what orientation it has landed.

Once secured to the surface, the lander will work as a laboratory on the comet. Experiments include analyzing the plasma and magnetic environment, and the surface and subsurface temperature. The lander will also drill and collect samples from beneath the surface, delivering them to the onboard laboratory for analysis. The interior structure of the comet will also be explored by sending radio waves through the surface towards the orbiting Rosetta.

Gathering the big picture

Comets are time capsules containing primitive material left over from the epoch when the Sun and its planets formed. By studying the gas, dust and structure of the nucleus and organic materials associated with the comet, via both remote and surface observations, the Rosetta mission could become a key to unlocking the history and evolution of our Solar System, as well as answering questions regarding the origin of Earth’s water and perhaps even life.

The Rosetta mission is administered by the European Space Agency (ESA), a multinational cooperative space effort.

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