Britney E. Schmidt

Vesta's shape and morphology

A New Dawn Since 17 July 2011, NASAs spacecraft Dawn has been orbiting the asteroid Vesta—the second most massive and the third largest asteroid in the solar system (see the cover). Russell et al. (p. 684) use Dawns observations to confirm that Vesta is a small differentiated planetary body with an inner core, and represents a surviving proto-planet from the earliest epoch of solar system formation; Vesta is also confirmed as the source of the howardite-eucrite-diogenite (HED) meteorites. Jaumann et al. (p. 687) report on the asteroids overall geometry and topography, based on global surface mapping. Vestas surface is dominated by numerous impact craters and large troughs around the equatorial region. Marchi et al. (p. 690) report on Vestas complex cratering history and constrain the age of some of its major regions based on crater counts. Schenk et al. (p. 694) describe two giant impact basins located at the asteroids south pole. Both basins are young and excavated enough amounts of material to form the Vestoids—a group of asteroids with a composition similar to that of Vesta—and HED meteorites. De Sanctis et al. (p. 697) present the mineralogical characterization of Vesta, based on data obtained by Dawns visual and infrared spectrometer, revealing that this asteroid underwent a complex magmatic evolution that led to a differentiated crust and mantle. The global color variations detailed by Reddy et al. (p. 700) are unlike those of any other asteroid observed so far and are also indicative of a preserved, differentiated proto-planet. Spacecraft data provide a detailed characterization of the second most massive asteroid in the solar system. Vesta’s surface is characterized by abundant impact craters, some with preserved ejecta blankets, large troughs extending around the equatorial region, enigmatic dark material, and widespread mass wasting, but as yet an absence of volcanic features. Abundant steep slopes indicate that impact-generated surface regolith is underlain by bedrock. Dawn observations confirm the large impact basin (Rheasilvia) at Vesta’s south pole and reveal evidence for an earlier, underlying large basin (Veneneia). Vesta’s geology displays morphological features characteristic of the Moon and terrestrial planets as well as those of other asteroids, underscoring Vesta’s unique role as a transitional solar system body.

Water, heat, bombardment: The evolution and current state of (2) Pallas

Dawn space mission will provide the first, detailed data of two of the major bodies in the Main Belt, Vesta and Ceres. In the framework of our studies on the origin of Solar System, we modelled the accretion of Jupiter and, through an N-Body code developed on purpose, we evaluated the flux of impactors on Vesta and Ceres keeping track of their formation zones. We also studied the effects of the possible inward migration of Jupiter on the rate and the characteristics of the impacts. We here describe the different scenarios and their implications for the evolution of Solar System. Dawn mission will provide detailed images of Vesta and Ceres surfaces and sup- ply crucial information to constrain their mineralogical and elemental composition through VIR, its imaging spectrometer. Thanks to these data, we will be able to study in depth the crater record on the surface of both Vesta and Ceres. We discuss here our study of the cratering process of Vesta and Ceres at the time of Jupiter formation. In our model we consider Jupiters gas accretion and displacement due to angular momentum exchange with the surrounding nebula. The gas accretion model used has been described in Coradini et al. (2004). Jupiters migration has been included to estimate the effect of increasing displacements. 2. Dynamical and physical model To explore the early collisional history of Vesta and Ceres we simulated the dy- namical evolution of a section of the young Solar System at the time of Jupiters core formation and the subsequent accretion of the gaseous envelope. Our template of the forming Solar System was composed of the Sun, the accreting Jupiter and a swarm of massless particles representing the planetesimals. The massless particles were initially distributed into a limited spatial region, which has been chosen to op- timise the computational requirements after a set of numerical experiments aiming