Collision rates in the present-day Kuiper Belt and Centaur Regions: Applications to surface activation and modification on Comets, Kuiper Belt Objects, Centaurs, and Pluto-Charon

We extend previous results showing that the surfaces of Edgeworth-Kuiper Belt objects are not primordial and have been moderately to heavily reworked by collisions. Objects smaller than about $r = 2.5$ km have collisional disruption lifetimes less than 3.5 Gyr in the present-day collisional environment and have been heavily damaged in their interiors by large collisions. In the 30--50 AU region, impacts of 1 km radius comets onto individual 100 km radius objects occur on $7\times10^7$--$4\times10^8$ yr timescales, cratering the surfaces of the larger objects with $\sim$8--54 craters 6 km in diameter over 3.5 Gyr. Collision time scales for impacts of 4 meter radius projectiles onto 1 km radius comets range from 3--5 $\times 10^7$ yr. The cumulative fraction of the surface area of 1 and 100 km radius objects cratered by projectiles with radii larger than 4 m ranges from a few to a few tens percent over 3.5 Gyr. The flux of EKO projectiles onto Pluto and Charon is also calculated and is found to be $\sim$3--5 times that of previous estimates. Our impact model is also applied to Centaur objects in the 5--30 AU region. We find the collisional/cratering histories of Centaurs are dominated by the time spent in the Edgeworth-Kuiper Belt rather than the time spent on planet-crossing orbits. Hence, the predominant surface activity of Centaur objects like Chiron is almost certainly not impact-induced.Comment: 17 pages, 8 figures. Icarus, 2000, in pres

The Size-Frequency Distribution of the Zodiacal Cloud: Evidence from the Solar System Dust Bands

Recent observations of the size-frequency distribution of zodiacal cloud particles obtained from the cratering record on the LDEF satellite (Love and Brownlee 1993) reveal a significant large particle population (100 micron diameter or greater) near 1 AU. Our previous modeling of the Solar System dust bands (Grogan et al 1997), features of the zodiacal cloud associated with the comminution of Hirayama family asteroids, has been limited by the fact that only small particles (25 micron diameter or smaller) have been considered. This was due to the prohibitively large amount of computing power required to numerically analyze the dynamics of larger particles. The recent availability of cheap, fast processors has finally made this work possible. Models of the dust bands are created, built from individual dust particle orbits, taking into account a size-frequency distribution of the material and the dynamical history of the constituent particles. These models are able to match both the shapes and amplitudes of the dust band structures observed by IRAS in multiple wavebands. The size-frequency index, q, that best matches the observations is approximately 1.4, consistent with the LDEF results in that large particles are shown to dominate. However, in order to successfully model the `ten degree' band, which is usually associated with collisional activity within the Eos family, we find that the mean proper inclination of the dust particle orbits has to be approximately 9.35 degrees, significantly different to the mean proper inclination of the Eos family (10.08 degrees).Comment: 49 pages total, including 27 figure pages. Submitted to Icaru

Collisional evolution in the Vulcanoid region: Implications for present-day population constraints

We explore the effects of collisional evolution on putative Vulcanoid ensembles in the region between 0.06 and 0.21 AU from the Sun, in order to constrain the probable population density and population structure of this region today. Dynamical studies have shown that the Vulcanoid Zone (VZ) could be populated. However, we find that the frequency and energetics of collisional evolution this close to the Sun, coupled with the efficient radiation transport of small debris out of this region, together conspire to create an active and highly intensive collisional environment which depletes any very significant population of rocky bodies placed in it, unless the bodies exhibit orbits that are circular to ~10^-3 or less, or highly lossy mechanical properties that correspond to a fraction of impact energy significantly less than 10% being imparted to ejecta. The most favorable locale for residual bodies to survive in this region is in highly circular orbits near the outer edge of the dynamically stable Vulcanoid Zone (i.e., near 0.2 AU), where collisional evolution and radiation transport of small bodies and debris proceed most slowly. If the mean random orbital eccentricity in this region exceeds ~10^-3, then our work suggests it is unlikely that more than a few hundred objects with radii larger than 1 km will be found in the entire VZ; assuming the largest objects have a radius of 30 km, then the total mass of bodies in the VZ down to 0.1 km radii is likely to be no more than ~10^-6Mearth, <10^-3 the mass of the asteroid belt. Despite the dynamical stability of large objects in this region (Evans & Tabachnik 1999), it is plausible that the entire region is virtually empty of km-scale and larger objects.Comment: text plus 7 .ps figures, gzipped. Icarus, 2000, in pres

Collisional Formation and Modeling of Asteroid Families

In the last decade, thanks to the development of sophisticated numerical codes, major breakthroughs have been achieved in our understanding of the formation of asteroid families by catastrophic disruption of large parent bodies. In this review, we describe numerical simulations of asteroid collisions that reproduced the main properties of families, accounting for both the fragmentation of an asteroid at the time of impact and the subsequent gravitational interactions of the generated fragments. The simulations demonstrate that the catastrophic disruption of bodies larger than a few hundred meters in diameter leads to the formation of large aggregates due to gravitational reaccumulation of smaller fragments, which helps explain the presence of large members within asteroid families. Thus, for the first time, numerical simulations successfully reproduced the sizes and ejection velocities of members of representative families. Moreover, the simulations provide constraints on the family dynamical histories and on the possible internal structure of family members and their parent bodies.Comment: Chapter to appear in the (University of Arizona Press) Space Science Series Book: Asteroids I

Collisional and dynamic evolution of dust from the asteroid belt

The size and spatial distribution of collisional debris from main belt asteroids is modeled over a 10 million year period. The model dust and meteoroid particles spiral toward the Sun under the action of Poynting-Robertson drag and grind down as they collide with a static background of field particles

Origin and evolution of the zodiacal dust cloud

The astrophysical importance of the zodiacal cloud became more apparent. The most useful source of information on the structure of the zodiacal cloud is the Infrared Astronomical Satellite (IRAS) observations. A substantial fraction of the extensive IRAS data set was analyzed. Also, a numerical model was developed (SIMUL) that allows to calculate the distribution of night-sky brightness that would be produced by any particular distribution of dust particle orbits. This model includes the effects of orbital perturbations by both the planets and solar radiation, it reproduces the exact viewing geometry of the IRAS telescope, and allows for the eccentricity of the Earth's orbit. SIMUL now is used to model not just the solar system dust bands discovered by IRAS but the whole zodiacal cloud

The origin and evolution of the zodiacal dust cloud

We have now analyzed a substantial fraction of the IRAS observations of the zodiacal cloud, particularly in the 25 micron waveband. We have developed a gravitational perturbation theory that incorporates the effects of Poynting-Robertson light drag (Gomes and Dermott, 1992). We have also developed a numerical model, the SIMUL mode, that reproduces the exact viewing geometry of the IRAS telescope and calculates the distribution of thermal flux produced by any particular distribution of dust particle orbits (Dermott and Nicholson, 1989). With these tools, and using a distribution of orbits based on those of asteroidal particles with 3.4 micron radii whose orbits decay due to Poynting-Robertson light drag and are perturbed by the planets, we have been able to: (1) account for the inclination and node of the background zodiacal cloud observed by IRAS in the 25 micron waveband; (2) relate the distribution of orbits in the Hirayama asteroid families to the observed shapes of the IRAS solar system dustbands; and (3) show that there is observational evidence in the IRAS data for the transport of asteroidal particles from the main belt to the Earth by Poynting-Robertson light drag