PDS_VERSION_ID = PDS3 RECORD_TYPE = "STREAM" LABEL_REVISION_NOTE = "T. Farnham; 27 Sept 2006 Created 2007-06-20 SBN:McLaughlin tempel1_cart.lbl: changed Wild 2 to Tempel 1, added latest version of catalog files, changed archive_status to locally archived, fixed record_type in dataset.cat, voldesc.cat, added checksum.tab/lbl to aareadme.txt; " OBJECT = DATA_SET DATA_SET_ID = "DIF-C-HRIV/ITS/MRI-5-TEMPEL1-SHAPE-V1.0" OBJECT = DATA_SET_INFORMATION DATA_SET_NAME = "PLATE SHAPE MODEL OF COMET 9P/TEMPEL 1, V1.0" DATA_SET_COLLECTION_MEMBER_FLG = "N" DATA_SET_TERSE_DESC = "Detailed plate shape model of comet 9P/Tempel 1" START_TIME = "N/A" STOP_TIME = "N/A" DATA_SET_RELEASE_DATE = 2006-11-01 PRODUCER_FULL_NAME = {"Tony L. Farnham", "Peter C. Thomas"} DETAILED_CATALOG_FLAG = "N" DATA_OBJECT_TYPE = "TABLE" ABSTRACT_DESC = "Shape model of comet 9P/Tempel 1, as derived from the Deep Impact images obtained around the time of closest approach to the comet." ARCHIVE_STATUS = "LOCALLY ARCHIVED" CITATION_DESC = "Farnham, T.L. and Thomas, P.C, SHAPE MODEL OF COMET TEMPEL 1, DIF-C-HRIV/ITS/MRI-5-TEMPEL1-SHAPE-MODEL-V1.0, NASA Planetary Data System, 2006." DATA_SET_DESC = " 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 Impact spacecraft around the time of closest approach. Additional information about the model can be found in Thomas et al., 'The Shape, Topography and Geology of Tempel 1 from Deep Impact Observations', Submitted to Icarus, 2007 [THOMASETAL2007] The Deep Impact (DI) spacecraft consists of two parts, an impactor and a flyby spacecraft, that encountered comet 9P/Tempel 1 on July 4, 2005. During this encounter, the impactor collided with the nucleus to produce a crater and expose sub-surface material that could be observed by the flyby spacecraft. During the final approach to the nucleus, three cameras, the High Resolution Instrument (HRI), the Medium Resolution Instrument (MRI) and the Impactor Targeting System (ITS) obtained hundreds of images of the nucleus. After the impact, in which the ITS was destroyed, the MRI and HRI continued to image the nucleus for 800 seconds, until the spacecraft entered shield mode and stopped tracking the nucleus. While in shield mode, the spacecraft passed its closest approach to the comet (500 km). Thirty minutes after closest approach, the spacecraft again reacquired the nucleus and obtained additional images as it departed. The images used for producing the shape model are contained in the PDS archive of Deep Impact Data for Tempel 1. The data set IDs are: DIF-C-HRIV-2-9P-ENCOUNTER-V1.0 DII-C-ITS-2-9P-ENCOUNTER-V1.0 DIF-C-MRI-2-9P-ENCOUNTER-V1.0 PLATE MODEL A detailed plate model was derived from 70 of the images, using control points to constrain the shape of the nucleus. 189 different features on the surface were selected as the control points, with 1520 measurements used in the model determination. Approximately 30% of the surface is well-defined from these control points, with the rest of the surface estimated using other constraints. These additional constraints include the positions of the limb and terminator (in both the approach and lookback images) and the photometric lightcurve of the nucleus that was measured in the weeks leading up to the encounter. Adjustments to the shape were also made to shift the moment of inertia in such a way that the spin axis of the nucleus would reproduce the rotation that was observed during the approach to the comet. The orientation of the spin axis is such that the positive pole points to a right ascension of 294 deg and a declination of +73 deg (J2000), with an uncertainty of approximately 5 deg. The prime meridian is defined by the center of the 350 meter crater located to the west of the impact site (in geographic coordinate). Thus, because longitude increases in the direction defined by the right hand rule around the positive pole, the longitude of the impact site is at about 15 degrees. The latitude is -26 degrees. The model, TEMPEL1_PLAN.TAB, is presented in body-centered planetocentric coordinates, with vertices at intervals of 2 degrees in both latitude and longitude. It consists of 16471 vertices, forming 32400 plates. The radial distance is given in kilometers and ranges from a minimum of 2.3260 km to a maximum 3.9564 km. The shape is such that it is not well represented by a triaxial ellipsoid. A second version of the model, TEMPEL1_CART.TAB, was derived from the planetocentric version. In this version, the vertices are in the same locations, but are presented in cartesian coordinates. The X axis is defined in the direction of the intersection of the equator and the prime meridian, the Z axis lies along the positive pole and the Y axis completes the right-hand coordinate system. For detailed analysis of the shape, routines such as the SURFACE and POLYSHADE routines in IDL can be used. To simply view the shape model, go to the browse directory, where the shape model has been converted to VRML format. There are two versions, one with the illumination that mimics that during the encounter, and one that uses a headlight to reveal the structure in a different manner. These models can be viewed using any standard VRML viewer. Author ------ The descriptions in this file were written by Tony Farnham. " CONFIDENCE_LEVEL_NOTE = " Confidence Level Overview ========================= The uncertainties in the pole orientation are approximately 5 degrees. In the regions that are well-defined by control points, the radial uncertainty of the plate model is approximately 20 m. In regions not defined by control points, the uncertainties are likely to be larger. Review ====== The plate model is sceduled for review on Nov 2006. " END_OBJECT = DATA_SET_INFORMATION OBJECT = DATA_SET_MISSION MISSION_NAME = "DEEP IMPACT" END_OBJECT = DATA_SET_MISSION OBJECT = DATA_SET_REFERENCE_INFORMATION REFERENCE_KEY_ID = "THOMASETAL2007" END_OBJECT = DATA_SET_REFERENCE_INFORMATION OBJECT = DATA_SET_TARGET TARGET_NAME = "9P/TEMPEL 1 (1867 G1)" END_OBJECT = DATA_SET_TARGET OBJECT = DATA_SET_HOST INSTRUMENT_HOST_ID = "DIF" INSTRUMENT_ID = {"HRIV","MRI"} END_OBJECT = DATA_SET_HOST OBJECT = DATA_SET_HOST INSTRUMENT_HOST_ID = "DII" INSTRUMENT_ID = "ITS" END_OBJECT = DATA_SET_HOST END_OBJECT = DATA_SET END