1,721,357 research outputs found
Non-destructive collisions and the evolution of the orbits of binary asteroid systems in the Main Belt
No full textThe effect of collisions on the stability of binary asteroids is discussed. The following mechanisms are taken into account: (1) complete disruption of one of the members of the system and (2) increase of linear momentum imparted by non-disruptive collisions. The latter effect is found to progressively increase the orbital energy of the systems up to the limit of binary gravitational instability.
We focus on the case of binary asteroids belonging to the Main Belt. We show that the probability that a binary system 'evaporates' before collisional disruption of one of the two members is not negligible. As a consequence, the expected lifetime of a binary system can decrease significantly. Binary 'evaporation' causes the two former members to continue to exist as independent asteroids forming a so-called asteroid pair.
The efficiency of this mechanism critically depends on the properties of the binary system and on the collisional environment. Several different scenarios have been taken into account concerning the size distribution of possible projectiles in the asteroid Main Belt, while the estimate of the fragmentation threshold in energetic impacts is based on the work of Benz & Asphaug. We estimate the expected average lifetime of a binary system as a function of different parameters including the size of the primary, the size ratio of the members and the orbital properties of the system. Moreover, the expected lifetimes of binary asteroids which are known today have been computed as a function of different possible collisional environments
An Improved Semi-Empirical Model of Catastrophic Impact Processes I-Theory and Laboratory Experiments
No full textSeveral improvements to the semi-empirical approach to the physics of catastrophic breakup events (see P. Paolicchi, A. Cellino, P. Farinella, and V. Zappalà,Icarus77, 187–212, 1989) have been recently developed and are described in the present paper. The main new features of the model consist of the derivation of a set of realistic, non-overlapping fragments, as well as of a better treatment of the role played by gravitational effects. The main physical results obtained by means of the improved model in situations similar to those encountered in laboratory experiments are discussed, and compared with the experimental evidence and with the outcomes of hydrodynamical simulations, as well as with the analogous results found in the previous version of the model. The present model appears as being able to fit, also quantitatively, the experiments, and to enlight hidden interrelations among various observed properties, in spite of its simplified physics. The problems related to the possibility of deriving reliable fragment mass distributions are pointed out and extensively discussed. The systematic extension of the present model to the cases in which gravitational effects are dominating will be postponed to a forthcoming paper
CATASTROPHIC FRAGMENTATION AND FORMATION OF FAMILIES: PRELIMINARY RESULTS FROM A NEW NUMERICAL MODEL
No full textPreliminary results of an improved version of the semiempirical model for catastrophic break up processes developed by Paolicchi et al., (1989) are presented. Among the several changes with respect to the old version, the most important seem to be related to the new treatment of gravitational effects, including self-compression and reaccumulation of fragments. In particular, the new model is able to analyze processes involving both cm-sized objects, like those studied by means of laboratory experiments, as well as much larger bodies, for which self- gravitational effects are dominant; moreover, in this latter case the model seems in principle adequate to describe with the same physics very different phenomena, like the formation of plausible asteroid families and the creation of single, rapidly spinning, objects. This fact, if confirmed by refined analyses, may be of high importance for our general understanding of asteroid collisional evolution
ASTEROID COLLISIONAL EVOLUTION - AN INTEGRATED MODEL FOR THE EVOLUTION OF ASTEROID ROTATION RATES
No full textWe combine experimental data and theoretical results to develop a model for the changes in the rotation rates of fragments produced by large collisions that break up and disperse asteroidal targets. Collisions that partially disperse the target can also produce a despinning of the reaccumulated core due to the angular momentum "splash" effect arising from the preferential escape of material with higher than average angular momentum (Cellino et al. 1990, Paper I). Combining these results with previously published work on spin rate changes for cratering impacts (Harris 1979; Dobrovolskis & Burns 1984), we present a comprehensive model for the changes in asteroid spin rates due to collisions. This spin change algorithm, when incorporated into an existing simulation of collisional effects on asteroid sizes, produces an integrated model for studying the simultaneous evolution of asteroid sizes and spin rates over solar system history. In order to understand collisional changes in spin rates in our model, we systematically explore a four-dimensional model parameter space with fixed initial size and spin distributions for the asteroids. We select low and high values of the four important parameters of the model, chosen to span the reasonable range of parameter space, and consider both strain-rate dependent and strain-rate independent scaling of impact strengths. Thirty-two collisional scenarios are generated and analyzed with regard to the change in the spin rate as a function of asteroid size. We conclude that: The spin evolution is strongly coupled to the size evolution. The observed relative spin-down of asteroids 100 km in diameter is likely to be the result of the angular momentum "splash" effect. Experimentally derived values of fragment spin parameters lead to predictions of faster than observed rotation rates for small asteroids. The spin rates of all asteroids except possibly the largest ones have been significantly altered by collisions over solar system history. In general, shattering impacts are much more important than cratering events in changing the spin of asteroids
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