Data Set Overview : This data set presents the different shape models of comet 81P/Wild 2,as derived from the Stardust navigation camera images that wereobtained around the time of closest approach to the comet. The firstmodel is a basic tri-axial ellipsoid shape describing the axial ratiosand their orientation. The second is a detailed plate shape model.Additional details and information about the ellipsoidal model can befound in Duxbury et al. J. Geophys. Res., Vol. 109, No. E12, E12S0210.1029/2004JE002316 (2004) [DUXBURYETAL2004]. Additional informationabout the plate model can be found in Kirk et al., 36th Annual Lunarand Planetary Science Conference, March 14-18, 2005, #2244 (2005)[KIRKETAL2005]. On 2 January 2004, the STARDUST spacecraft flew past comet 81P/Wild 2and took 72 images. In these images, the phase angle started at 70 degduring the approach, dropped to 3 deg near closest approach, and thenincreased to 110 deg during the departure. Most images were obtainedwithin a range of 2,000 km, with the closest at 237 km. The cameratook the images using a broadband filter and a CCD that had an angularresolution of 57 microrad/pixel. These images are archived in the PDSStardust NAVCAM Data for comet Wild 2 (Data_Set_Name: STARDUST NAVCAMIMAGES OF WILD 2, Data_Set_ID: SDU-C-NAVCAM-2-EDR-WILD2-V1.0) TRI-AXIAL ELLIPSOID MODEL A tri-axial ellipsoid model was fit to the limb and terminator inall the Wild 2 nucleus images. The model was constrained by the factthat the viewing geometry changed by 180 degrees during the encounterand essentially the entire illuminated hemisphere of Wild 2 was viewedin these images (or ~50% of the surface, since there was no noticeablerotation during the few minutes that the images were taken). The axial dimensions determined from the visual fit of the model tothe limb and terminator were 1.65 x 2.00 x 2.75 km +/-0.05 km (1sigma). The illuminated limb is reasonably smooth, with the exceptionof a few large depressions. It is understood that half of the surfacewas not illuminated and that these unseen surfaces could deviate fromthe model derived from the illuminated regions. However the model fitto the terminator, even though quite rough due to topographicvariations, does give some evidence that the model probablyextrapolates to the unseen part of the nucleus to at least a km orbetter. A body-fixed coordinate system was established with the shortest axisassumed to be the rotation pole and the longest axis used to definethe prime meridian. The posigrade axis is defined to match thecorresponding poles determined by Sekanina (2003) [SEKANINA2003] andFarnham and Schleicher (2005) [FARNHAM&SCHLEICH2005] and is directedtoward the position (J2000) RA:110 deg, dec:-13 deg (+/-3 deg). PLATE MODEL A detailed plate model was derived from the same set of images.Pairs of these images were used to generate stereo views if thecomet and to determine the cartesian XYZ coordinates of points onthe surface. Excel was then used to perform translations toconvert the model to coordinates of latitude, longitude andelevation. Results are given in planetocentric coordinates. Themodel itself consists of 6432 points forming 12514 plates,covering the portions of the nucleus that were both illuminatedand visible during the encounter (about 50% of the totalsurface). A best fitting triaxial ellipsoid was fit to the plate model using aleast squares fit. This ellipsoid had the dimensions of 1.350 x 2.002x 2.607 km (this is slightly different from the ellipsoidal modeldescribed above because the earlier model merely reproduced anenvelope that enclosed the visible surface). Elevations relative tothis best-fitting ellipsoid range from -600 m to +250 m, with an RMSrange of heights of 93 m. The orientation of the minor axis (positivepole) of this ellipsoid is at a right ascension of 112 degrees and adeclination of -17 degrees (J2000.0). Four versions of the plate model are included here. The primaryversion (WILD2_CART_VIS.TAB) is given in Cartesian coordinates basedon a body-centered system. A second version (WILD2_PLAN_VIS.TAB) isgiven in planetocentric coordinates, with distances given from thecenter of the ellipsoid. In both of these versions, only the visibleand illuminated portions of the nucleus are included. Two additionalversions of the model (WILD2_CART_FULL.TAB and (WILD2_PLAN_FULL.TAB,respectively) again provide the shape models in Cartesian andplanetocentric coordinates, but include full coverage of the surfaceof the nucleus. In these versions, the non-visible portions of thesurface are represented by the best-fitting ellipsoid. For detailed analysis of the shape, routines such as the SURFACE andPOLYSHADE routines in IDL can be used. To simply view the shapemodel, go to the browse directory, where the shape model has beenconverted to VRML format. There are two versions, one with theillumination that mimics that during the encounter, and one that usesa headlight to reveal the structure in a different manner. Thesemodels can be viewed using any standard VRML viewer. Author------The descriptions in this file were written by Tony Farnham.

Confidence Level Overview : A visual fit was used to match the ellipsoid model to theobservations. Uncertainties were estimated by changing the parametersuntil an overlay of the model clearly deviated from the correspondingimages. Estimated errors are 0.05 km in the axial dimensions, and 3degrees in the angular measurements. The plate model has a horizontalresolution of approximately 50 meters and a vertical precision ofabout 6 meters.  Review :The ellipsoid model was peer reviewed on Oct 15, 2004 and accepted pendinga few minor corrections and additions, which have been applied. Theplate model is sceduled for review on Dec 12, 2005.