An asteroid is a minor planet—an object larger than a meteoroid (thus 1 meter or larger) that is neither a planet nor an identified comet—that orbits within the inner Solar System or is co-orbital with Jupiter (Trojan asteroids). Asteroids are rocky, metallic, or icy bodies with no atmosphere, and are broadly classified into C-type (carbonaceous), M-type (metallic), or S-type (siliceous). The size and shape of asteroids vary significantly, ranging from small rubble piles under a kilometre across to Ceres, a dwarf planet almost 1000 km in diameter. A body is classified as a comet, not an asteroid, if it shows a coma (tail) when warmed by solar radiation, although recent observations suggest a continuum between these types of bodies. Asteroids are a source of precious metals, and base metals for in-space use. Some elements exceed terrestrial ore grades: Ir/Ru/Os/Ni/Pt/Rh/Co/O/Pd/Fe/Mg/Rh/W/Au. Total PGM grades in iron meteorites are lower than previous estimates. Mineral processing can separate refractory metal nuggets and other components.
1*Dr. Pruthviraj K. Chaudhary, 1Dr. Dhiren L. Chaudhari, 2Dr. Dhrubo Jyoti Sen, 1Jay M. Patel, 1Krutik P. Patel, 1Het P. Patel (Sun,) studied this question.