22. The relation between orbits and physical characteristics of meteors

摘要: The relation of physical characteristics of meteors to their orbital elements is investigated using Harvard Super-Schmidt data. A set of characteristic indices is defined, allowing for the effects of geocentric velocity, angle of incidence, magnitude and mass, wherever a correction appears appropriate according to the correlations found by Jacchia et al. (1967). The medians for representative meteor samples are plotted in the semi-major axis/eccentricity diagram and the distribution of each parameter is derived. Although the differences are moderate compared to the measuring errors, six regions of different nature can be distinguished.The existence of two families of asteroidal meteors is indicated, one of them brought to crossing with the Earth's orbit by drag effects and the other by collision effects in the main asteroid belt. These meteors are characterized by low and uniform beginning heights, high fragmentation, low ablation, low deceleration, and bright wakes. A direct counterpart to this is represented by meteors moving in short-period orbits of higher eccentricity and shorter perihelion distance, which bear resemblance to the long-period and retrograde cometary meteors. Meteors with perihelion distances of less than 0·15 AU tend to resemble the bona fide asteroidal meteors by a progressive increase of fragmentation and decrease of reduced beginning heights and decelerations as the perihelion approaches the Sun. This is attributed to the selective destruction effects of solar radiation.With the exception of the Draconids, the mean characteristics of meteor showers agree well with those of sporadic meteors moving in similar orbits. It is suggested that the Draconid stream includes a broad variety of meteoric material and that the two peculiar Super-Schmidt meteors on record represent only the less resistive, short-lived component which has already been eliminated from the other showers.