1,721,035 research outputs found
Collisional evolution of asteroids constrained by their present rotational properties
No full textThe abundance of asteroids having unusually large angular momenta of rotation in the diameter range 200 - 300 km implies that, if these angular momenta have a collisional origin, the asteroid population was of the order of a few times the present one at the time when the orbits were stirred up and the disruptive collisional process begun. The meaning of this result and the issue of the collisional vs. "primordial" origin of the currently observed asteroid rotations are shortly discussed
Fragmentation of Hyperion and cratering of Saturn's satellites
No full textThe authors summarize the arguments suggesting a collisional fragmentation of the Saturnian satellite Hyperion, and a subsequent orbital evolution of the fragments controlled by Titan's resonant perturbations. As a consequence of this evolution, most fragments eventually either collided with Titan or were ejected from the system, but a minor fraction of them probably impacted with the inner moons and contributed to the cratering of their icy surface
Original abundance of asteroids from their present rotational properties
No full textA long-standing problem in Solar System evolution is the strong mass depletion that occurred in the asteroid zone. Recent collisional evolution models (Davis et al., 1985) suggest that comminution due to destructive impacts is responsible only for a small part of the mass loss, implying that at the end of the accretionary phase the belt mass was no more than several times the present mass. A similar conclusion can be independently reached by another line of evidence, relying on the present rotational properties of asteroids. The abundance of objects having unusually large angular momenta of rotation in the diameter range 200-300 km implies that, if these angular momenta have a collisional origin, approximately one third of these objects have been hit by projectile asteroids larger than about 65. About 450 such projectiles are currently available in the belt, yielding a 16 per cent impact probability against a 250-km-sized target over the Solar System's lifetime. Hence a moderate mass depletion (by a factor of the order of 5) is consistent with the present abundance of asteroids with rapid spins and elongated shapes
Collisional origin of asteroid families - Effects of the target's gravity
No full textThe outcomes of asteroidal catastrophic collisions are strongly affected by the target asteroid's gravity, since only the fragments escaping with initial velocities higher than the target's escape velocity are not reaccumulated into 'rubble pile' remnants. This idea can be compared with the observational evidence on the properties of family asteroids in several ways: (1) the shape and spin period of the 'reaccumulated' family asteroids will roughly fit the relationships valid for self-gravitating fluid bodies; (2) the relative velocities of the few escaping fragments arising from a breakup event marginally overcoming self-gravity will often have an anisotropic distribution, affecting the final distribution of orbital elements; and (3) the amount of mass which in a given family escaped to 'infinity' will be correlated with the target's size, since only for objects larger than approximately 100 km self-gravity plays an important role. These predictions are discussed and compared with the available data
Collisional outcomes in the asteroid belt
No full textIn order to study the outcomes of the major collisions endured by asteroids of different sizes, the projectile's kinetic energy (PKE) is compared with the energy needed to overcome the target's solid-state cohesion (expressed as SM, where M is target mass and the critical specific energy S ranges from 100,000 to 100 million erg/g, depending on the material properties) plus the target's self-gravitational energy. This latter is multiplied by a factor gamma, to account for energy losses due to dissipative processes. It is predicted that catastrophic fragmentation occurs and that a substantial part of the target's mass is dispersed to infinity when PKE SM + (3 gamma/5) (GMsq/R) where R is target radius. It is concluded that almost all asteroids are outcomes of catastrophic collisions, that caused either complete fragmentation of the target objects or, at least, drastic readjustments of their internal structure, shape and spin rate
The asteroids as outcomes of catastrophic collisions
No full textThe role of catastrophic collisions in the evolution of the asteroids is discussed in detail, employing extrapolations of experimental results on the outcome of high-velocity impacts. The probability of impacts with a given projectile-to-target mass ratio for asteroids of different sizes is derived, taking into account different mass distributions of the asteroid population at the beginning of the collisional process. The extrapolations show that collisional breakup against solid-state cohesions must be a widespread process for asteroids. The influence of self-gravitation and transfer of angular momentum during collision is shown to depend strongly on the target size, resulting in a variety of possible outcomes in the intermediate size range. Comparison of the theoretical results with observations of asteroid rotations and sshapes yields favorable results
Analysis of the spin rate distribution of asteroids
No full textA new analysis of the spin rate distribution of asteroids is performed; it attempts to take into account the principal selection effects and studies separately several different sub-samples, chosen according to the asteroid size range and taxonomic classification. The results show strong statistical evidence for a non-Maxwellian character of the overall distribution, mainly due to an excess of slowly rotating objects of small and intermediate size. It is also found that the average spin rate increases with size, while different taxonomic types present distinct features for their distributions. These results can be interpreted in terms of a complex and size-dependent collisional history of asteroids, with widespread fragmentation and the frequent formation of binary or multiple asteroids
Some ideas for semiempirical theory of catastrophic impact processes among asteroids
No full textThe authors are able to investigate the size-velocity-spin properties of fragments, as well as to guess what could happen if the target was previously fractured. The model should be used either to interpret laboratory results or to understand the properties of collisional evolution in the asteroidal belt
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