Rosetta probe Philae to land on comet’s head

A group of engineers and scientists have scrutinised data and chose a relatively smooth and well-lit landing site for the European Space Agency’s Rosetta lander, Philae, on comet 67P/Churyumov-Gerasimenko.

The group met at CNES (Centre national d’études spatiales – national centre for space studies) in Toulouse, France, this past weekend to choose the primary and backup landing sites on the comet.

The primary site, dubbed Site J, is on the head of comet and offers unique scientific potential, minimum risk to the lander, good illumination and has few boulders, the European Space Agency (ESA) said. The backup site, Site C, is on the body of the comet.

The 100kg Philae is scheduled to descend to the comet at a walking pace over seven hours, and using harpoons and ice screws, latch onto its surface on 11 November. Once in place, Philae will perform in-depth measurements to characterise the nucleus of the comet.

Landing a probe on a comet for very first time

Stephan Ulamec, Philae lander manager at the German Aerospace Center in Cologne, Germany, said that while the comet is scientifically exciting, its shape makes it operationally challenging. Not to mention the fact no one has ever attempted to land anything on a comet before.

“None of the candidate landing sites met all of the operational criteria at the 100pc level, but Site J is clearly the best solution,” Ulamec said.

Landing site factors the engineers and scientists had to take into consideration include a safe trajectory for deploying Philae to the surface, few hazards in the landing zone, the balance of daylight and night-time hours, and the frequency of communications passes with Rosetta.

Site J also receives sufficient sunlight to recharge Philae and continue operations on the comet’s surface beyond the initial battery-powered phase. 

Philae’s primary landing site on Site J on comet 67P/Churyumov–Gerasimenko. Image via ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM

Time is of the essence

An operational timeline will now be prepared to determine the precise approach of Rosetta in order to land Philae on Site J.

The landing must take place before mid-November, as the comet is predicted to grow more active as it moves closer to the sun, the ESA said.

“Of course, we cannot predict the activity of the comet between now and landing, and on landing day itself,” said ESA Rosetta flight director Andrea Accomazzo from the European Space Operations Centre in Darmstadt, Germany.  

“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.”

Role of Rosetta

Launched in March 2004, Rosetta was reactivated in January after a record 957 days in hibernation. Composed of an orbiter and lander, Rosetta’s objectives since arriving at comet 67P/Churyumov-Gerasimenko earlier this month are to study the comet up close in unprecedented detail, prepare for landing the probe on the comet’s surface, and track the comet’s changes through next year, as it sweeps past the sun.

The resulting data will help scientists learn more about the origin and evolution of our solar system and the role comets may have played in seeding Earth with water, and perhaps even life.