Catastrophic disruption of icy bodies with sub-surface oceans

Several icy bodies in the outer Solar system have extensive internal oceans. In several bodies the oceans are believed to be so extensive they decouple the interior core from the icy surface. A major evolutionary driver in the Solar System is high speed impacts – which lead to cratering or even disruption of the target body. Here we consider how the presence of an internal ocean modifies the energy density needed to disrupt an icy body with an internal ocean. We find that in laboratory experiments on decimetre scale bodies, the energy density to cause disruption is 16.25 ± 1.35 J kg−1, compared to 18.0 ± 0.7 J kg−1 for solid ice bodies. This suggests that for the purposes of impacts the bodies behave as if a solid with the same density. Predictions of the lifetimes of such icy bodies against impact disruption thus need not take the interior ocean into account

Laboratory tests of catastrophic disruption of rotating bodies

The results of catastrophic disruption experiments on static and rotating targets are reported. The experiments used cement spheres of diameter 10 cm as the targets. Impacts were by mm sized stainless steel spheres at speeds of between 1 and 7.75 km s?1. Energy densities (Q) in the targets ranged from 7 to 2613 J kg?1. The experiments covered both the cratering and catastrophic disruption regimes. For static, i.e. non-rotating targets the critical energy density for disruption (Q*, the value of Q when the largest surviving target fragment has a mass equal to one half of the pre-impact target mass) was Q* = 1447 ± 90 J kg?1. For rotating targets (median rotation frequency of 3.44 Hz) we found Q* = 987 ± 349 J kg?1, a reduction of 32% in the mean value. This lower value of Q* for rotating targets was also accompanied by a larger scatter on the data, hence the greater uncertainty. We suggest that in some cases the rotating targets behaved as static targets, i.e. broke up with the same catastrophic disruption threshold, but in other cases the rotation helped the break up causing a lower catastrophic disruption threshold, hence both the lower value of Q* and the larger scatter on the data. The fragment mass distributions after impact were similar in both the static and rotating target experiments with similar slopes

Book reviews

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43178/1/24_2004_Article_BF00879508.pd

Hypervelocity impact fragmentation of basalt and shale projectiles

Results are presented for the fragmentation of projectiles in laboratory experiments. 1.5 mm cubes and spheres of basalt and shale were impacted onto water at normal incidence and speeds from 0.39 to 6.13 km s−1; corresponding to peak shock pressures 0.7–32 GPa. Projectile fragments were collected and measured (over 100,000 fragments in some impacts, at sizes down to 10 µm). Power laws were fitted to the cumulative fragment size distributions and the evolution of the exponent vs. impact speed and peak shock pressure found. The gradient of each of these power laws increased with increasing impact speed/peak shock pressure. The percentage of the projectiles recovered in the impacts was found and used to estimate projectile remnant survival in different solar system impact scenarios at the mean impact speed appropriate to that scenario. For Pluto, the Moon and in the asteroid belt approximately 55%, 40% and 15%, respectively, of an impactor could survive and be recovered at an impact site. Finally, the catastrophic disruption energy densities of basalt and shale were measured and found to be 24 × 104 J kg−1 and 9 × 104 J kg−1, respectively, a factor of ∼2.5 difference. These corresponded to peak shock pressures of 1 to 1.5 GPa (basalt), and 0.8 GPa (shale). This is for near normal-incidence impacts where tensile strength is dominant. For shallow angle impacts we suggest shear effects dominate, resulting in lower critical energy densities and peak shock pressures. We also determine a method to ascertain information about fragment sizes in solar system impact events using a known size of impactor. The results are used to predict projectile fragments sizes for the Veneneia and Rheasilvia crater forming impacts on Vesta, and similar impacts on Ceres

Asteroid families

Liczba asteroid o wyznaczonych orbitach przekracza obecnie 500 tysięcy. Wiele z nich jest ze sobą powiązanych genetycznie, gdyż stanowią one produkt uszkodzenia lub nawet rozbicia większej asteroidy w procesie zderzeniowym. Podstawowy problem stanowi przypisanie (lub nie) danej asteroidy do określonej rodziny. Całkowicie jednoznacznej metody nie ma. W zbiorze asteroid potencjalnie tworzących rodzinę znajdują się zawsze obiekty „obce” (interlopery). Podstawowa metoda identyfikacji to HCM (Hierarchical Clustering Metod – metoda hierarchicznego grupowania). Rodziny zawierają od kilku asteroid do nawet około 30 tysięcy asteroid. Znanych rodzin jest około 100. Około 20-30% wszystkich asteroid to członkowie jakiejś rodziny

STICKING EXPERIMENTS AND NON-GRAVITATIONAL COMPONENT OF THE MECHANISM OF THE GROWTH OF PLANETS

Des expériences sur la jonction métal-métal produite par des collisions de moyenne vitesse (de 50 à 650 m/s) ont été effectuées. Les résultats des collisions sont présentés dans le plan de coordonnées : angle de collision - vitesse de collision. L'application de ces résultats aux problèmes d'accrétion en Planétologie est étudiée.The experiments concerning collisional sticking of metallic bodies (Pb, Sn, Fe) have been performed. The impact velocity range was 50 to 650 m/s. The mapping of the results of collisions (rebound, sticking, partial sticking) in the impact angle - impact velocity plane was made. The application of this results to planetary accretion problems is presented

The impact origin of Eunomia and Themis families

Criteria for finding asteroid families (Zappala et al. 1995) are applied to a large (205,770 member) data set of asteroid orbital elements. The cases of the Eunomia and Themis families are considered as examples. This is combined with the cratering criteria for catastrophic disruption of small bodies in the solar system (Leliwa-Kopystyński et al. 2008). We find that the Eunomia parent body itself was not catastrophically disrupted in the family-generating impact event; after impact, the current body contains as much as 70% of its primordial mass. However, by contrast with Eunomia, the present mass of 24 Themis is only about 21% of that of its primordial body. Limits are placed on the sizes of the impactors in both examples, and for the case of Eunomia, the radius of the just sub-critical crater (which may be present on 15 Eunomia) is predicted as 58 km.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202