NASA Logo, National Aeronautics and Space Administration
NASA Space Science Data Coordinated Archive Header

PLATE SHAPE MODEL OF COMET 9P/TEMPEL 1 V2.0 (PDS)

NSSDCA ID: PSSB-00543

Availability: Archived at NSSDC, accessible from elsewhere

Description

This description was generated automatically using input from the Planetary Data System.

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 and by the Stardust spacecraft around the times of their respective closest approaches. Additional information about the model can be found 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 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 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 72 NAVCAM 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 at intervals of 2 degrees in both latitude and longitude. The radial distance is given in kilometers and ranges from a minimum of 2.10 km to a maximum 3.97 km. The shape is such that it is not well represented by a triaxial ellipsoid, and the center of figure is not exactly coincident with the origin of the coordinate system. (This issue may be corrected in a future version of the shape model, but the current offset is smaller than the uncertainties in 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 visible portions of the nucleus (~70%). Additional constraints were obtained using the silhouette of the limb, though the uncertainty on these determinations is larger, 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 such that the positive pole points to a right ascension of 255 deg and a declination of +64.5 deg (J2000), with an uncertainty of approximately 3 deg (a position about 16 deg different from the orientation presented in version 1 of the shape model). This result may not represent an instantaneous spin vector, but instead represents the orientation that best reproduces the views in both the DI and Stardust images. The prime meridian is defined by the center of the 350 meter crater located to the west of the DI 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 16 degrees. The latitude is -28 degrees. Two versions of the shape model are included. The first is the original model (TEMPEL1_2012_PLAN.TAB) derived as noted above, given in planetocentric coordinates. The table includes a list of 16022 vertices, with connectivity for forming 32040 plates. The format follows the standard PDS shape model definition (see PLATE_SHAPE_DEFINITION.TXT in the documents directory). In addition, each vertex includes a code that denotes the primary constraint on its 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 document TEMPEL1_SHAPE_DESCRIPTION.ASC. A second version of the model (TEMPEL1_2012_CART.WRL), was derived from the planetocentric version and presents the vertices in Cartesian coordinates. In this coordinate system, 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. The Cartesian coordinate version of the model is presented with a VRML wrapper that allows it to be displayed with existing VRML viewers that are freely available (e.g., INSTANT PLAYER, OCTAGA, CORTONA, etc.) Different camera angles and illumination conditions have been embedded in the WRL file to display the nucleus as it would appear during various key times during the two encounters, with the associated solar illumination (though the twist angle around the line of sight may not match what is recorded in the corresponding images). There are also embedded viewpoints from all of the principal axis directions, with the 'headlight' illumination. Note that the capabilities of different viewers may limit the ability to display some or all of these viewpoints. Look for 'cameras' or 'navigation' items in the menus. 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 on information from [THOMASETAL2013B] and communications with Peter Thomas, the shape model creator.

These data are available on-line from the Planetary Data System (PDS) at:

http://pdssbn.astro.umd.edu/holdings/dif-c-hriv_its_mri-5-tempel1-shape-v2.0/

Alternate Names

  • DIF-C-HRIV/ITS/MRI-5-TEMPEL1-SHAPE-V2.0

Discipline

  • Planetary Science: Small Bodies

Additional Information

Spacecraft

Experiments

Questions and comments about this data collection can be directed to: Dr. David R. Williams

 

Personnel

NameRoleOriginal AffiliationE-mail
Dr. Ray L. Newburn, Jr.Data ProviderNASA Jet Propulsion Laboratorynewburn@scn1.jpl.nasa.gov
Dr. Michael F. A'HearnData ProviderUniversity of Maryland
Dr. Tony FarnhamGeneral ContactUniversity of Marylandfarnham@astro.umd.edu
Dr. Peter C. ThomasGeneral ContactCornell University
[USA.gov] NASA Logo - nasa.gov