• Characterizing and navigating small bodies with imaging data

      Gaskell, R. W.; Barnouin-Jha, O. S.; Scheeres, D. J.; Konopliv, A. S.; Mukai, T.; Abe, S.; Saito, J.; Ishiguro, M.; Kubota, T.; Hashimoto, T.; et al. (The Meteoritical Society, 2008-01-01)
      Recent advances in the characterization of small body surfaces with stereophotoclinometry are discussed. The principal data output is an ensemble of landmark maps (L-maps), high-resolution topography/albedo maps of varying resolution that tile the surface of the body. Because they can have a resolution comparable to the best images, and can be located on a global reference frame to high accuracy, L-maps provide a significant improvement in discriminatory power for studies of small bodies, ranging from regolith processes to interior structure. These techniques are now being used to map larger bodies such as the Moon and Mercury. L-maps are combined to produce a standard global topography model (GTM) with about 1.57 million vectors and having a wide variety of applications. They can also be combined to produce high-resolution topography maps that describe local areas with much greater detail than the GTM. When combined with nominal predictions from other data sources and available data from other instruments such as LIDAR or RADAR, solutions for the spacecraft position and camera pointing are the most accurate available. Examples are drawn from studies of Phobos, Eros, and Itokawa, including surface characterization, gravity analysis, spacecraft navigation, and incorporation of LIDAR or RADAR data. This work has important implications for potential future missions such as Deep Interior and the level of navigation and science that can be achieved.
    • Global mapping of the degree of space weathering on asteroid 25143 Itokawa by Hayabusa/AMICA observations

      Ishiguro, M.; Hiroi, T.; Tholen, D. J.; Sasaki, S.; Ueda, Y.; Nimura, T.; Abe, M.; Clark, B. E.; Yamamoto, A.; Yoshida, F.; et al. (The Meteoritical Society, 2007-01-01)
      We obtained color images of near-Earth asteroid 25143 Itokawa by the Hayabusa multiband imaging camera to characterize the regional color properties. Images were obtained for the whole disk from the gate position (GP) and home position (HP) at a spatial resolution of 0.8-3.7 m/ pixel. Whole-disk spectra are adjusted to the telescopic data obtained by the University of Hawai'is 88-inch telescope using the Eight Color Asteroid Survey (ECAS) system. The disk-resolved measurements show large variations in the three visible channels. We present a map of an index related to the degree of space weathering, which has been newly developed based on laboratory measurements. We find large variations in the degree of space weathering on Itokawa. Fresh materials are observed in regions of steep slopes and craters, whereas mature materials are ubiquitously distributed. This result suggests that pristine ordinary chondrite-like materials have been exposed through weathered layers by excavation. By also examining close-up images obtained during touchdown rehearsal, we find that most rocks in Itokawas rough terrains are weathered. Instead of a regolith blanket, the surface of this small asteroid is covered with weathered rocks and gravels.