مقاله انگلیسی رایگان در مورد مدت بقای سیارک ها در حرکت چرخشی سیاره ها – الزویر ۲۰۱۸

Discovery statistics. The 1999 discovery of the first asteroid in retrograde orbit was so unusual, such that the suggested name was the ananym of the word ’asteroid’:  Dioretsa. This unusual minor body has been observed for a long time (since its precovery in 1998) and is still classified as a Centaur. At the present time a great number of asteroids with i > 90◦ are known. For sake of brevity, we will use a short term for such objects: retrograde aster10 oids. When we started studying this asteroid group around 2008, we had only 22 discovered objects, of which a few were numbered. Furthermore, a few of the studied objects were later reclassified as comets. Despite this, the number of classified asteroids is constantly increasing (Fig. 1). 15 Hypotheses of origin. So far, there is no consistent hypothesis on the origin of retrograde asteroids. Since the number of these objects is relatively small, their lifetimes must be short, therefore the ’production’ mechanism is probably not effective. According to some authors, particular res20 onances with giant planets can play an important role in this mechanism. It has been proven that some well known resonances, such as a 3:1 with Jupiter, can produce NEA orbits with extreme inclinations (Greenstreet et al., 2012). de la Fuente Marcos and de la Fuente Marcos (2014) also 1pawel.kankiewicz@ujk.edu.pl Figure 1: The discovery statistics of retrograde asteroids: the cumulative number of known small bodies in retrograde orbits, without objects re-classified as comets. 25 suggested that higher order resonances with giant planets correlate with the ’chaotic’ production of retrograde orbits. There may exist a hypothetical reservoir of these objects located at a great distance from the Sun, acting as a source of eccentric and extremely inclined orbits. This could be the Oort Cloud. Similarities to comets. Unusual values of inclinations raise the suspicion that most of the bodies in retrograde orbits are simply inactive comets. This hypothesis can be cautiously proposed when looking at the distribution of 35 bright comets, since approximately 20% of them have a retrograde motion. However, this is not the only criterion used for drawing similarities between these types of orbits and cometary trajectories. The criteria proposed by Tancredi (2014) for classifying asteroids and comets take into account the Tisserands parameter, the Minimum Orbital Intersection Distance (MOID), and the aphelion and perihelion distances. The use of these criteria leads to the identification of a group of asteroids known as ACOs: ’Asteroids in Cometary Orbits’,– which includes some retro45 grade asteroids. In the work of Licandro et al. (2016), some asteroids were mentioned as possible candidates for being potential comets, therefore, it is possible to find more comets among the population of retrograde asteroids. Our previous studies (Kankiewicz and W lodarczyk, 2010, 2014) 50 confirmed many cases of revealed cometary activity in this sub-population.