August 25, 2014 – Five candidate sites for the Philae lander have been identified on Comet 67P/Churyumov-Gerasimenko. The Landing Site Selection Group group used detailed information collected by the European Space Agency’s Rosetta spacecraft during its first two weeks orbiting the comet to identify potential sites to set down the lander in November.
This will mark the first time a landing on a comet has ever been attempted. Philae will drill into the surface, extract and analyze samples, and send pictures and data back to Earth.
Choosing the right landing site is a complex process. The site must balance the technical needs of the orbiter and lander during all phases of the separation, descent, and landing, and during operations on the surface with the scientific requirements of the ten instruments on board Philae.
“Based on the particular shape and the global topography of Comet 67P/ Churyumov-Gerasimenko, it is probably no surprise that many locations had to be ruled out,” said Stephan Ulamec, Lander Manager at DLR. “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.”
The sites were assigned a letter from an original pre-selection of 10 possible sites, which does not signify any ranking. Three sites (B, I and J) are located on the smaller of the two lobes of the comet and two sites (A and C) are located on the larger lobe.
The next step is a comprehensive analysis of each of the candidate sites, to determine possible orbital and operational strategies that could be used for Rosetta to deliver the lander to any of them. At the same time, Rosetta will move to within 50 km of the comet, allowing a more detailed study of the proposed landing sites.
By 14 September, the five candidate sites will have been assessed and ranked, leading to the selection of a primary landing site, for which a fully detailed strategy for the landing operations will be developed, along with a backup.
During this phase, Rosetta will move to within 20–30 km of the comet, allowing even more detailed maps of the boulder distributions at the primary and backup landing sites to be made. This information could be important in deciding whether to switch from primary to backup.
Rosetta’s rendezvous with Comet 67P/Churyumov-Gerasimenko has opened a new chapter in Solar System exploration. Comets are considered to be the building blocks of the Solar System and may have helped to seed the Earth with water, making life possible. Rosetta will help answer fundamental questions about the origin and evolution of our solar system and the role that comets may have played.
The comet is on a 6.5-year orbit around the Sun and today is 522 million km from it. At their closest approach on 13 August 2015, just under a year from now, the comet and Rosetta will be 185 million km from the Sun, meaning an eightfold increase in the light received from the Sun.
While Rosetta and its scientific instruments will watch how the comet evolves as heating by the Sun increases, observing how its coma develops and how the surface changes over time, the lander Philae and its instruments will be tasked with making complementary in situ measurements at the comet’s surface. The lander and orbiter will also work together using the CONSERT experiment to send and detect radio waves through the comet’s interior, in order to characterise its internal structure.
The orbiter’s payload includes the Alice ultraviolet spectrograph developed by the Southwest Research Institute (SwRI) in Boulder. Alice will analyze gases in the comet’s coma, which is the bright envelope of gas around the nucleus of the comet, and developed as a comet approaches the sun. Alice will also measure the rate at which the comet produces water, carbon monoxide and carbon dioxide. These measurements will provide valuable information about the surface composition of the nucleus.
Rosetta is an ESA mission with contributions from its member states and NASA. Rosetta’s Philae lander is provided by a consortium led by DLR, MPS, CNES and ASI. Airbus Defense and Space built the Rosetta spacecraft. NASA’s Jet Propulsion Laboratory (JPL) manages the U.S. contribution of the Rosetta mission for NASA’s science mission directorate in Washington, under a contract with California Institute of Technology (Caltech). JPL also built the Microwave Instrument for the Rosetta Orbiter and hosts its principal investigator, Dr. Samuel Gulkis.
Southwest Research Institute (San Antonio, TX and Boulder, CO) developed the Rosetta orbiter’s Ion and Electron Sensor and Alice Instrument and hosts their principal investigators, Dr. James Burch (IES) and Dr. Alan Stern (Alice).
Rosetta’s 10-year journey began in March 2004. The rendezvous between the orbiter and Comet 67P/C-G occurred on August 6, 2014.