Data Set Overview
  =================
    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 2
    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]

Confidence Level Overview
  =========================
    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.