Asteroids

The first asteroid, Ceres, was discovered on the first night of the nineteenth century. There are now more than 800,000 numbered asteroids. Numerous properties link most meteorite groups to asteroids. These include cooling rates, the presence in some specimens of solar-wind gas, formation ages and CRE ages, orbital parameters, and the retrieval of chondritic material from asteroids visited by spacecraft. In addition, the spectral reflectance properties of meteorites match those of particular asteroids. Space-weathering can account for differences between OC spectra and those of S-complex and Q-complex asteroids. Ordinary-chondrite parent asteroids probably initially had an onion-shell-like structure due to internal heating by 26 Al. These bodies were likely collisionally disrupted and gravitationally reassembled while still hot.