1,721,052 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
The period distribution of eclipsing and spectroscopic binary systems. I
No full textThe period distribution of eclipsing and spectroscopic binary systems was analysed by various methods to take into account selection effects on observational data, with the purpose of deriving the actual distribution curve. The discussion of results shows the presence of some secondary maxima in the distribution which are probably of a nonstatistical character. They could be regarded as an indirect clue to the discrete nature of the star formation process, according to the spiral density wave theory of galactic evolution by Lin et al. (1969)
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
The Psyche Family: Collisionally destroyed or never formed?
No full textAsteroid 16 Psyche, the largest M-type asteroid, is widely considered to be the collisionally exposed core of an ~500-km diameter differentiated parent body which was similar to asteroid 4 Vesta. However, there is no dynamical family associated with Psyche nor are there spectroscopic data for the existence of the mantle or crustal material from the parent body. The usual explanation for the missing material requires that the Psyche parent body was collisionally disrupted early in solar system history, followed by collisional grinding of the family down to below the current observational limit sizes. We test the exposed core hypothesis for the origin of Psyche using a numerical code that simultaneously calculates both the collisional evolution of the asteroid belt and the model family formed by the breakup of the Psyche parent body (PPB). We find that it would take a projectile about 300-350 km in size to thoroughly disrupt a 500-km asteroid (the estimated size of the PPB), and that the probability of such an event occurring in the first 500 Ma of solar system history is only about 1%. While the Psyche model family is found to have been significantly ground down subsequent to its formation, there should be several tens of survivors from the mantle and crust larger than ~10 km that should be spectroscopically detectable by current technology. Although only a small fraction of the asteroids larger than 10 km have been discovered and observed spectroscopically to date, none have been identified as potential survivors from the PPB (Burbine et al. 1996, Meteor. Planet. Sci. 31, 607-620). Given the low probability of the disruption of a Vesta-like body and the lack of either dynamical or observational confirmation of a family or material from the parent body, we think it more likely that Psyche has possibly been shattered by impacts but not catastrophically disrupted. In this case, it would be a plausible candidate parent body for the mesosiderites. The exposed-core scenario more probably applies to other, smaller (diameter <~100 km) M-type asteroids, which could be the parent bodies of the iron meteorites. However, this interpretation raises the interesting problem of why among the larger asteroids only Vesta and the PPB would have been fully differentiated
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
Collision rates and impact velocities in the Trojan asteroids swarms
No full textCollision rates and impact velocities for Trojan asteroids have been estimated by a robust numerical approach, based on a parallel computation of orbits over time spans of ~10^4 year and the subsequent statistical analysis of the resulting close encounter data bases. The average intrinsic collision probabilities for the two Trojan swarms are 6.46 x 10^-18 km^-2 year^-1 (L_4) and 5.30 x 10^-18 km^-2 year^-1 (L_5), namely about twice the corresponding value for the main asteroid belt. Collision speeds range from ~1 to 14 km/sec, with a mean value close to 5 km/sec. These findings suggest that the intensity of the collisional process is about the same in the Trojan swarms as in the main belt, and are consistent with the detection of dynamical families among Trojans. The collisional flux in the Trojan regions is very anisotropic, with a dominant component perpendicular to the invariable plane. Subtle dynamical mechanisms are likely to somewhat affect the Trojan collision rates, but their understanding requires further work on the very long-term evolution of Trojan orbits
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