On the Origins of Earth-Approaching Asteroids

Abstract

It is generally accepted that Main-Belt asteroids (MBAs) and nuclei of no longer active comets are the sources that replenish the Amor, Apollo, and Aten groups of asteroids, i.e., Earth-approaching asteroids (EAAs). Investigations of the dynamics of EAAs and numerical modeling of their orbital motion have shown that the so-called resonance mechanism of the replenishment of the EAA population with objects from the Main Belt is quite sufficient for its maintenance. In this paper, we compare the physical properties of EAAs and MBAs (and, partly, cometary nuclei) in an effort to gain an understanding of whether the physical properties of EAAs can tell us anything about their origins. The principal result of the performed analysis is the conclusion that the small dimensions of EAAs; their MBA-identical set of taxonomic classes; the identical mineralogy and preponderance of differentiated compositions among EAAs; and their, on average, MBA-identical shape, rotation, optical properties, and surface structure are all convincing proof that the Main Belt is the dominant source of the replenishment of the EAA population and that the share of cometary-origin EAAs does not exceed 10%. The most likely candidates for cometary-origin objects among EAAs are 2100 Ra-Shalom, 2101 Adonis, 2201 Oljato, 2212 Hephaistos, 3200 Phaethon, 3552 Don Quixote, and 4015 Wilson-Harrington.