9:00 AM - 9:15 AM
[PPS03-19] The shape of Bennu: Implications for internal structure.
Keywords:(101955) Bennu, Asteroids, OSIRIS-REx mission
Digital Terrain Model Construction from Imaging: About 1500 OCAMS images with ground sample distance ranging from 30 to 200 m were used to develop the global DTM of Bennu. We used distant limb data of Bennu to construct an initial DTM of Bennu. Then a combination of geometric stereo data and surface lighting conditions (or photoclinometry) modeled small patches (or maplets) of terrain across the asteroid. Geometric stereo typically defines the location of the center of each maplet, while the surface tilts across the maplet are estimated by best fitting the brightness variations of images that contain some portion of the maplet. These maplets are then combined to build a global model. The model increases in detail, accuracy, and precision as higher-resolution images and images with different viewing conditions are incorporated.
Digital Terrain Model Construction from Laser Altimetry: We collated several six-hour linear scans obtained by OLA during orbit around Bennu to make an independent shape model of Bennu at a resolution equivalent to the one derived from imaging. This DTM is improved relative to the SPC-derived model because OLA better resolves the heights, and extent of 1 to 3m boulders across the surface of the asteroid.
Bennu’s Geomorphological and Structural Properties: The evaluation of the both models shows that the average size of the asteroid is 490.06 ± 0.16 m.
The model shows the presence of several features:
-An equatorial ridge that is muted, and is diamond-shaped when viewed from the pole;
-Topographic north-south ridges that extend in some instances from pole to pole. The ridges influence the distribution of boulders, which are frequently concentrated between the ridges;
-Large craters that influence some of the attributes of the shape, primarily along the equator;
-A few large protruding boulders >40 m in diameter and >10 m high, mostly in the southern hemisphere;
-Grooves, scarps, and troughs that in some instances extend several 10s to 100s of meters, with depths ranging from 2–10 m.
Conclusion: The initial shape characteristics suggest that Bennu has some interior stiffness. Considering past modeling efforts investigating deformation due to spin-up, the lack of a circular equatorial ridge with a pronounced bulge, and the presence of high standing north-south ridges indicate that in spite of an abundance of evidence for material moving towards the equator, Bennu has interior structure that resists deformation.