Data Set Information
DATA_SET_NAME PLATE SHAPE MODEL OF COMET 9P/TEMPEL 1 V2.0
DATA_SET_ID DIF-C-HRIV/ITS/MRI-5-TEMPEL1-SHAPE-V2.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : This data set presents the detailed plate shape model of comet 9P/Tempel 1,as derived from the images of the comet that were obtained by the Deep Impactspacecraft and by the Stardust spacecraft around the times of theirrespective closest approaches. Additional information about the model can befound in Thomas et al., 'The Nucleus of comet 9P/Tempel 1 from two flybys',Icarus 222, 453-466, 2013. [THOMASETAL2013B]. The Deep Impact (DI) spacecraft consists of two parts, an impactor and aflyby spacecraft, that encountered comet 9P/Tempel 1 on July 4, 2005. Duringthis encounter, the impactor collided with the nucleus to produce a craterand expose sub-surface material that could be observed by the flybyspacecraft. During the final approach to the nucleus, three cameras, the High ResolutionInstrument (HRI), the Medium Resolution Instrument (MRI) and the ImpactorTargeting System (ITS) obtained hundreds of images of the nucleus. After theimpact, in which the ITS was destroyed, the MRI and HRI continued to imagethe nucleus for 800 seconds, until the spacecraft entered shield mode andstopped tracking the nucleus. While in shield mode, the spacecraft passedits closest approach to the comet (500 km). Thirty minutes after closestapproach, the spacecraft again reacquired the nucleus and obtained additionalimages as it departed. The Stardust spacecraft visited comet Tempel 1 during its extended mission(Stardust New Exploration of Tempel 1, or Stardust NEXT). On February 14,2011, the spacecraft flew by the comet at a distance of 182 km, obtaining 72NAVCAM images, centered on the time of closest approach. The data set IDs for the images used to produce the shape model are: DIF-C-HRIV-2-9P-ENCOUNTER-V1.0** DIF-C-MRI-2-9P-ENCOUNTER-V1.0 DII-C-ITS-2-9P-ENCOUNTER-V1.0 SDU-C/CAL-NAVCAM-2-NEXT-TEMPEL1-V1.0 ** HRI data contributed in very early Deep Impact work, including determining how the nucleus rotated and analyzing limbs in the lookback images. PLATE MODEL The shape model was derived in planetocentic coordinates with vertices atintervals of 2 degrees in both latitude and longitude. The radial distanceis given in kilometers and ranges from a minimum of 2.10 km to a maximum 3.97km. The shape is such that it is not well represented by a triaxialellipsoid, and the center of figure is not exactly coincident with the originof the coordinate system. (This issue may be corrected in a future versionof the shape model, but the current offset is smaller than the uncertaintiesin the vertex measurements.) The plate model was derived from a combination of DI and Stardust images,using 480 different control points to constrain the shape of the visibleportions of the nucleus (~70%). Additional constraints were obtained usingthe silhouette of the limb, though the uncertainty on these determinations islarger, due to the ambiguity in where the limb lies along the line of sight. The orientation of the spin axis, derived as part of the solution, is suchthat the positive pole points to a right ascension of 255 deg and adeclination of +64.5 deg (J2000), with an uncertainty of approximately 3 deg(a position about 16 deg different from the orientation presented in version1 of the shape model). This result may not represent an instantaneous spinvector, but instead represents the orientation that best reproduces the viewsin both the DI and Stardust images. The prime meridian is defined by thecenter of the 350 meter crater located to the west of the DI impact site (ingeographic coordinate). Thus, because longitude increases in the directiondefined by the right hand rule around the positive pole, the longitude of theimpact site is at about 16 degrees. The latitude is -28 degrees. Two versions of the shape model are included. The first is the originalmodel (TEMPEL1_2012_PLAN.TAB) derived as noted above, given in planetocentriccoordinates. The table includes a list of 16022 vertices, with connectivityfor forming 32040 plates. The format follows the standard PDS shape modeldefinition (see PLATE_SHAPE_DEFINITION.TXT in the documents directory). Inaddition, each vertex includes a code that denotes the primary constraint onits derivation (control points, limb silhouette, or not well constrained)providing a measure of the accuracy of the derived radius at that point.Additional information is provided in the documentTEMPEL1_SHAPE_DESCRIPTION.ASC. A second version of the model (TEMPEL1_2012_CART.WRL), was derived from theplanetocentric version and presents the vertices in Cartesian coordinates.In this coordinate system, the X axis is defined in the direction of theintersection of the equator and the prime meridian, the Z axis lies along thepositive pole and the Y axis completes the right-hand coordinate system. The Cartesian coordinate version of the model is presented with a VRMLwrapper that allows it to be displayed with existing VRML viewers that arefreely available (e.g., INSTANT PLAYER, OCTAGA, CORTONA, etc.) Differentcamera angles and illumination conditions have been embedded in the WRL fileto display the nucleus as it would appear during various key times during thetwo encounters, with the associated solar illumination (though the twistangle around the line of sight may not match what is recorded in thecorresponding images). There are also embedded viewpoints from all of theprincipal axis directions, with the 'headlight' illumination. Note that thecapabilities of different viewers may limit the ability to display some orall of these viewpoints. Look for 'cameras' or 'navigation' items in themenus. Table: Shape Model Characteristics Area: 108 km^2 Volume: 95.2 km^3 Radius of eq. volume sphere: 2.83 +/- 0.1 km Radius range: 2.10-3.97 km Gravity: 0.030-0.038 cm s^2 (for mean density 470 kg m^3) Axis Orientation: RA: 255 deg, Dec: 64.5 deg (J2000) Model moment ratios (A,B,C are the principal moment of inertia axes): A/C: 0.688 B/C: 0.930 Body model moment orientations: A: -2.7 deg, 16.8 deg E B: -3.4 deg, 107.0 deg E C: +80.6 deg, 247.5 deg E Author------The descriptions in this file were written by Tony Farnham, based oninformation from [THOMASETAL2013B] and communications with PeterThomas, the shape model creator.
DATA_SET_RELEASE_DATE 2013-01-08T00:00:00.000Z
START_TIME 1965-01-01T12:00:00.000Z
STOP_TIME N/A (ongoing)
MISSION_NAME DEEP IMPACT
MISSION_START_DATE 2005-01-12T12:00:00.000Z
MISSION_STOP_DATE 2005-07-13T12:00:00.000Z
TARGET_NAME 9P/TEMPEL 1 (1867 G1)
TARGET_TYPE COMET
INSTRUMENT_HOST_ID DIF
DII
SDU
INSTRUMENT_NAME DEEP IMPACT HIGH RESOLUTION INSTRUMENT - VISIBLE CCD
DEEP IMPACT IMPACTOR TARGETING SENSOR - VISIBLE CCD
DEEP IMPACT MEDIUM RESOLUTION INSTRUMENT - VISIBLE CCD
NAVIGATION CAMERA
INSTRUMENT_ID HRIV
ITS
MRI
NAVCAM
INSTRUMENT_TYPE CCD CAMERA
IMAGING CAMERA
NODE_NAME Small Bodies
ARCHIVE_STATUS ARCHIVED
CONFIDENCE_LEVEL_NOTE Confidence Level Overview : The uncertainty in the pole orientation is approximately 3 deg. In the regions that are well-defined by control points, the radialuncertainty of the plate model is approximately 60 m. (These errors aredominated by uncertainties in the geometries from the three spacecraft thatintroduce inconsistencies in the feature positions in common regions.) Inregions not defined by control points, silhouettes provide the constraints,with uncertainties of ~100 m dominated by the ambiguity of where the limblies along the line of sight. Points unconstrained by either of thesemethods may have errors 100-300 m. Review :The plate model was reviewed March 5, 2013.
CITATION_DESCRIPTION Farnham, T.L. and Thomas, P.C, PLATE SHAPE MODEL OF COMET 9P/TEMPEL 1 V2.0, DIF-C-HRIV/ITS/MRI-5-TEMPEL1-SHAPE-MODEL-V2.0, NASA Planetary Data System, 2013.
ABSTRACT_TEXT Plate shape model of comet 9P/Tempel 1, as derived from Deep Impact and Stardust NEXT images obtained around the times of closest approach to the comet.
PRODUCER_FULL_NAME Tony L. Farnham
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