Asteriod Sizes and Albedos
Abstract
The radiometric method of determining diameters of asteroids is reviewed, and a synthesis of radiometric and polarimetric measurements of the diameters and geometric albedos of a total of 187 asteroids is presented. All asteroids with diameters greater than 250 km are identified, and statistical studies can be carried out of the size distributions of different albedo classes down to 80km diameter for the entire main asteroid belt (2.03.5 AU). The distribution of albedos is strongly bimodal, with mean albedos for the C and S groups of 0.035 and 0.15, respectively. The C asteroids outnumber the S at all sizes and all values of semimajor axis, increasing from a little over half the population inside 2.5 AU to more than 95% beyond 3.0 AU; for all objects with D > 70 km, the ratio C/(C+S) is 0.88 ± 0.04. More than half of all asteroids in this size range have a > 3.0 AU. The M asteroids constitute about 5% of the population for a < 3.0 AU, but no members of of this class have been identified in the outer belt. There are no significant differences between the distributions of C, S, and M asteroids for the largest asteroids ( D > 200 km) and for those of intermediate size (200270 km). The total mass in the belt, down to 70km size, but excluding Ceres, is about 2 × 10 ^{24} g. Evidence is presented that several large asteroids rotate in a prograde sense, and that a real difference existsbetween the bulk densities of Ceres and Vesta.
 Publication:

Icarus
 Pub Date:
 June 1977
 DOI:
 10.1016/00191035(77)900343
 Bibcode:
 1977Icar...31..185M
 Keywords:

 Albedo;
 Asteroids;
 Diameters;
 Polarimetry;
 Radiometers;
 Size Determination;
 Classifications;
 Density (Mass/Volume);
 Frequency Distribution;
 Infrared Detectors;
 Photometry;
 Surface Temperature;
 Tables (Data);
 Lunar and Planetary Exploration