Jets and sources of activity on 67P observed by OSIRIS J.-B. Vincent, H. Sierks, L. Lara, P. Gutierez, R. Rodrigo, M. Pajola, N. Oklay, J. Knollenberg, I. Bertini, Z.-Y. Lin, W.-H. Ip, N. Thomas, B. Davidsson, S. Mottola, S. Lowry, S. Fornasier, D. Bodewits, M. Massironi, S. Marchi, S. Hviid, H.U. Keller, S. Besse, L. Jorda, O. Groussin, M. A’Hearn, S. Höfner, C. Snodgrass, and the OSIRIS team OSIRIS team OSIRIS Full Team Meeting 07-10 Oct. 2014

19P/Borelly, Deep Space 1 2001 1P/Halley, GIOTTO 1986 103P/Hartley 2, EPOXI 2010 Comets might be primordial objects at their core, but they have experienced significant surface processing. We need to understand this evolution if we want to link current observations to the origin of the Solar System. How does activity work ? Why some regions are more active than others ? What is the link between coma and surface features ? What is the minimal scale of activity ? Can we identify active areas ? Do we understand which regions will become active in 6 months ? In one year ?

Monitoring 67P's activity with OSIRIS Coma structures in WAC images, July 25-26 2014, 3.67 AU, 3000 km, 300 m/px. At least 3 dust features detected, rotating with the nucleus. Inversion of coma structures links them to bright spots on the nucleus surface, mainly in the transition region between the two lobes. NAC: 50m/px

WAC images, August 05-06 2014, 3.60 AU, 175 km, 12 m/px One large feature visible, focused in a narrow jet some time during the rotation. Combination of projection effect and temporal variation as the illumination conditions are changing with the rotation. Work ongoing on assessing the energy balance and thermal effects. By observing the activity from different angles, we can link dust features in the coma to specific regions on the surface, and morphologic/color information.

Relative brightness Azimuthal profiles at 3km from the nucleus. What fraction of the dust production comes from that particular active source ? We compared brightness in the jet, with average brightness on both sides, ignoring regions affected by ghosts and stray light. "Neck Jet" contributes approximately 10% to the total dust production. The rest of the dust likely comes from smaller jets and/or isotropic emission from the comet's surface.

Linking jets to surface features Red-Green-Blue lines = XYZ axis Black dashed line = jet direction Yellow line = Sun Blue facets = inverted sources Detect jet in images Calculate geometry of observation from shape model + SPICE kernels. Calculate intersection between plane Spacecraft/jet-center and shape model, no constraints on illumination or facet orientation. Repeat for several images => probability map of active sources Use source in forward model, compare output with original images

Modeling Inversion and small scale jets by J.-B. Vincent, COSSIM code 06Aug_04:20 Inversion and small scale jets by J.-B. Vincent, COSSIM code Large scale features modeled by Steve Lowry and Agata Makiela

Increasing resolution… Most jets originate from the neck region and seem correlated to the brightest patches on the surface, as well as outcrops and cliffs. The main jets is actually composed of many small ones, down to a few pixels width. Inversion complicated by the large concavity of this area.

Source(s)? Large cliffs Crack (+ small pits ?) Smooth terrain Outcrops Boulders Small cliffs Pits

Sources ?

Sources ? NAC Twisted jet ! How does it work ?

Activity everywhere Background activity distributed all over the body, what is the main driver ? From August to October: - helio dist went from 3.6 to 3.2 AU, too cold for water ? - sub/Sun latitude went from +45° to +40°

GAS_O1_4

Existing models/Predictions "neck" N activity at perihelion ilumination on landing day, ellipsoid model Vincent et al, A&A, 2013 Inversion of jets from 2003 and 2009 apparitions "most of the activity is located close to the equator and in the southern hemisphere, with only one active region in the north. [...] this region is partially depleted of volatile material, the ice being for instance buried under a deeper layer of dust than in other regions."

Summary 67P is active We see large temporal and spatial variations Stronger activity in the transition region between the two lobes, new regions are waking up everywhere Work ongoing on determining precise source locations, and modeling dust features "Active pits" detected, geomorphological study and continuous monitoring in progress (next talk) Existing models of activity still valid for the jets and their sources