On the relative numbers of C types and S types among near-earth asteroids

The discovery circumstances of the near-earth asteroids (NEAs) were modeled in order to investigate the observational selection effects associated with NEAs. It is suggested that these selection effects are responsible for the apparent overabundance of S types among the NEAs and that this overabundance is in part a result of the larger phase darkening of the C types over the S types. The large phase angles and preferential phase darkening of the C type NEAs force some of them below the threshold of detectability (in a magnitude-limited survey), thus exaggerating the number of S type NEAs. 23 refs.