Comets: Rosetta results and related science
Icy structures and terrain in comet 67P
Max K Wallis
Chandra Wickramasinghe: BCAB Buckingham Univ. and ISPA, Gifu, Japan
BCAB, Buckingham University
Despite the comet’s very black crust, Rosetta’s remarkable images show several indicators of an underlying icy morphology. Comet 67P displays smooth, planar ‘seas’ (the largest 600mx 800m) and flat-bottomed craters, both features seen also on comet Tempel-1. Comet 67P’s surface is peppered with mega-boulders (10-70km) like comet Hartley-2, while parallel furrowed terrain appears as a new ice feature. The largest sea (‘Cheops’ Sea, 600 x 800m) curves around one lobe of the 4km diameter comet, and the crater lakes extending to ~150m across are re-frozen bodies of water overlain with organic-rich debris (sublimation lag) of order 10 cm. The parallel furrows relate to flexing of the asymmetric and spinning two-lobe body, which generates fractures in an underlying body of ice. The mega-boulders are hypothesised to arise from bolide impacts into ice. In the very low gravity, boulders ejected at a fraction of 1m/s would readily reach ~100m from the impact crater and could land perched on elevated surfaces. Where they stand proud, they indicate stronger refrozen terrain or show that the surface they land on (and crush) sublimates more quickly. Outgassing was already evident in September at 3.3AU, with surface temperature peaks of 220-230K, which implies loosely bound H2O and/or unconsolidated organic mixtures. Increasing rates of gassing as Rosetta follows comet 67P around its 1.3 AU perihelion will hopefully reveal the activation of possible micro-organisms as well as the nature and prevalence of near-surface ices.
13:30 - 15:00