Mathematics – Logic
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.p31a0977a&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #P31A-0977
Mathematics
Logic
6055 Surfaces And Interiors, 6094 Instruments And Techniques, 6205 Asteroids And Meteoroids, 6297 Instruments And Techniques
Scientific paper
Near-Earth Objects (NEOs) present an important scientific question and an intriguing space hazard. They are scrutinized by a number of large, dedicated groundbased telescopes, and their diverse compositions are represented by thousands of well-studied meteorites. A successful program of NEO spacecraft exploration has begun, and we are proposing Deep Interior as the next logical step. Our mission objective is to image the deep interior structure of two NEOs using radio reflection tomography (RRT), in order to explore the record of asteroid origin and impact evolution, and to test the fundamental hypothesis that these important members of the solar system are rubble piles rather than consolidated bodies. Asteroid Interiors. Our mission's RRT technique is like a CAT scan from orbit. Closely sampled radar echoes yield volumetric maps of mechanical and compositional boundaries, and measure interior material dielectric properties. Exteriors. We use color imaging to explore the surface expressions of unit boundaries, in order to relate interior radar imaging to what is observable from spacecraft imaging and from Earth. Gravity and high fidelity geodesy are used to explore how interior structure is expressed in shape, density, mass distribution and spin. Diversity. We first visit a common, primitive, S-type asteroid. We next visit an asteroid that was perhaps blasted from the surface of a differentiated asteroid. We attain an up-close and inside look at two taxonomic archetypes spanning an important range of NEO mass and spin rate. Scientific focus is achieved by keeping our payload simple: Radar. A 30-m (tip-to-tip) cross-dipole antenna system operates at 5 and 15-MHz, with electronics heritage from JPL's MARSIS contribution to Mars Express, and antenna heritage from IMAGE and LACE. The 5-MHz channel is designed to penetrate >1 km of basaltic rock, and 15-MHz penetrates a few 100 m or more. They bracket the diversity of solar system materials that we are likely to encounter, and are richly complementary. Imaging. We fly a 100% redundant camera whose primary function is to provide accurate navigation and geodesy in support of radio reflection tomography. This camera also yields stereo color imaging for geology and RRT-related compositional analysis. We image the interiors of two frequently Earth-crossing asteroids: 1999 ND43 is a yet-unnamed S-type. Its diameter (~0.5 km) and spin period (11.4 hr) are known, from which initial mapping plans are derived. It is probably a very common asteroid type. Nyx is one of the best-examined asteroids of its size (~1 km). Its faster spin period (4.4 hr) and shape are known. A V-type spheroid with distinct basaltic composition, Nyx is either a differentiated small planet with crust, mantle and core, or more likely, a fragment or assemblage of fragments ejected from the crust of a larger planetoid.
Asphaug Erik
Belton Michael
Klaasen Ken
Ostro Steve
Plaut Jeffrey J.
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