Description of the Asteroid (101955) Bennu Radar Shape Model bundle V1.1 ======================================================================== Bundle Generation Date: 2021-10-26 Peer Review: Neese_Richardson_Mueller_Migration Discipline node: Small Bodies Node Content description for the Asteroid (101955) Bennu Radar Shape Model bundle ============================================================================ Note: This bundle was migrated to PDS4 from the PDS3 data set EAR-A-I0037-5-BENNUSHAPE-V1.0. For PDS3 data sets migrated to PDS4, the following text is taken verbatim from the data set description and confidence level note of the PDS3 data set catalog file. In these cases, some details may not be correct as a description of the PDS4 bundle. Asteroid (101955) Bennu was discovered in September 1999 by the LINEAR survey and designated 1999 RQ36. It is an Apollo Near-Earth Object (NEO) with a semi-major axis of 1.126 AU, an eccentricity of 0.205 and an orbital inclination of 6 degrees. Bennu has a mean diameter of 492 meters (uncertainty: 20 meters) and a sidereal rotation period of 4.29746 hours (uncertainty: 0.002 hours). Bennu is a B-type asteroid characterized by a linear, featureless spectrum with bluish to neutral slope at visible wavelengths. Spectral analysis suggests that the most likely meteorite analogs for Bennu are the CI or CM meteorites (Clark et al., 2011). This shape model of asteroid (101955) Bennu was created by Nolan et al. (2013) based on radar and optical photometric observations made in 1999 and 2005. The model resolution is approximately 25 meters between vertices, with regions of higher resolution around the location of a topographical 'boulder' and the symmetric region in the opposite hemisphere. The model has the format v x1 y1 z1 v x2 y2 z2 v x3 y3 z3 (etc.) f i1 j1 k1 f i2 j2 k2 (etc.) where the letter 'v' denotes a vertex and the letter 'f' denotes a triangular facet. The VERTEX_TABLE is the first part, describing the positions of the vertices of the shape model. The floating point numbers x1 y1 z1 are the coordinates of vertex 1, and so on (vertices are implicitly numbered beginning with 1). The origin is the center of mass, and the axes are the principal axes of the shape model. The z-axis is the spin axis or positive pole. The units are kilometers. The linking of vertices into facets is provided in the FACET_TABLE. The Asteroid (101955) Bennu Shape Model - 101955bennu.tab - file is equivalent to the wavefront or .obj format. The file can be opened by software such as Blender, MATLAB, JSC3D, or CAD programs, and can read directly by most 3D printing services. A variety of free .obj viewers are available for download online. Multi-axis views of the model - bennu-model.pdf - is a .pdf of views of the asteroid along its principal axes. The Pole Orientation - pole.tab - file contains the pole latitude, longitude, and uncertainty in degrees. The Rotation State - rotate.tab - file contains the rotation rate and uncertainty in hours. Nolan, M.C., C. Magri, E.S. Howell, L.A.M. Benner, J.D. Giorgini, and 6 others, Shape Model and Surface Properties of the OSIRIS-REx Target Asteroid (101955) Bennu from Radar and Lightcurve Observations, Icarus 226, 629-640, doi:10.1016/j.icarus.2013.05.028, 2013. [NOLANETAL2013] Clark, B.E., R.P. Binzel, E.S. Howell, E.A. Cloutis, M. Ockert-Bell, and 10 others, Asteroid (101955) 1999 RQ36: Spectroscopy from 0.4 to 2.4 um and meteorite analogs, Icarus 216(2), 462-475, doi:10.1016/j.icarus.2011.08.021, 2011. [CLARKETAL2011B] Hergenrother, C.W., M.C. Nolan, R.P. Binzel, E.A. Cloutis, M.A. Barucci, and 11 others. Lightcurve, Phase and Color Photometry of the OSIRIS-REx Target Asteroid (101955) Bennu. Icarus, 226, 663-670, doi:10.1016/j.icarus.2013.05.044, 2013.[HERGENROTHERETAL2013] Krugly, Yu.N., I.N. Belskaya, V.G. Shevchenko, V.G. Chiorny, F.P. Velichko, and 7 others, The near-Earth objects follow-up program: IV. CCD photometry in 1996-1999, Icarus 158, 294-304, doi:10.1006/icar.2002.6884, 1999. [KRUGLYETAL1999] Caveats to the data user ======================== There exists some north-south symmetry in surface features of Benu. Because of the nearly-equatorial viewing geometry, this is an artifact of the radar data, and the varying degree of symmetry in different parts of the object may result from variable rotational coverage. As the asteroid rotates, the points on the equator move across the radar images, but points at the rotation pole remain motionless (Green, 1968). As a result, the Z dimension of the asteroid is less well determined than the X- and Y-dimensions: 'squeezing' the model in the Z direction does not change the radar images much. This coordinate system should not be used to define a cartographic system, as the principal axes are not uniquely determined due to the symmetry of the shape in terms of longitude. Uncertainties reported are 1-sigma, but for the shape parameters are conservative and somewhat subjective. Formal errors in the X- and Y-directions are of 10 meters, and in the Z-axis, 52 meters.