How scientists chose a safe spot on a giant cosmic duck
In short: Landing a spacecraft on a comet is a high-stakes balancing act. Engineers had to weigh scientific potential against the risk of landing on a surface that was becoming increasingly volatile as it approached the Sun, all while racing against a narrow window of sunlight and temperature stability.
The selection of the landing site for the Philae lander on comet 67P/Churyumov-Gerasimenko was a race against time. Following the rendezvous on 6 August, the Landing Site Selection Group (LSSG) engaged in an intense, six-week investigation to characterize the comet's nucleus. This meant determining its shape, rotation rate, orientation, gravity field, albedo, and surface temperature, while also quantifying the density and velocity of particles in the surrounding coma.
The comet's unusual 'duck' shape presented significant challenges. The LSSG evaluated five shortlisted candidate sites, which were narrowed down from an original pre-selection of 10 possible locations (labeled A through J). These sites were distributed across the comet's two lobes: three sites (B, I, and J) were on the smaller lobe, while two (A and C) were on the larger lobe. Each elliptical site covered roughly one square kilometer.
Ultimately, the team selected Agilkia as the primary target. Agilkia was chosen because it offered unique scientific potential—including hints of nearby activity—while presenting minimum risk to the lander compared to other candidates. The timing was equally critical; the landing had to occur when the comet was approximately 3 Astronomical Units (450 million km) from the Sun, around mid-November. This window ensured enough sunlight for Philae's solar cells to provide power, while avoiding the rising heat that could jeopardize a safe landing.
The mission was a massive international collaboration. While the ESA led the Rosetta mission, the Philae lander was provided by a consortium including the German Aerospace Center, the French National Space Agency, and the Italian Space Agency. The OSIRIS imaging system, which provided the critical data for site characterization, was supported by a wide array of European research institutes and funding agencies.
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Sources
- Summary by Intellect · source: Rosetta landing site choices
- Also: Selecting a landing site for Rosetta's lander, Philae - Rosetta - Science Portal
- Also: Four Rosetta Candidate Landing Sites - NASA Science
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