Section 5 Asteroid Belt

**211**

**Chapter 9**

*Katrin Krohn*

**Abstract**

impact into ice

**1. Introduction**

Special Crater Types on Vesta and

The exploration of two small planetary bodies by the Dawn mission revealed multifaced surfaces showing a diverse geology and surface features. Impact crater are the most distinctive features on these planetary bodies. The surfaces of asteroid Vesta and the dwarf planet Ceres reveal craters with an individual appearance as caused by different formation processes. Special topographic and subsurface conditions on both bodies have led to the development of special crater types. This chapter present the three most characteristic crater forms fund on both bodies. Asymmetric craters are found on both bodies, whereas ring-mold craters and

**Keywords:** asteroids, asymmetric craters, ring mold craters, floor-fractured craters,

The Dawn Mission was the first mission exploring two different planetary objects in the asteroid belt between Mars and Jupiter, the asteroid Vesta and the dwarf planet Ceres. Asteroid Vesta is the second most massive asteroid (2.59079 x 1020 kg) with a mean diameter of 525 km and a mean density of 3.456 ± 0.035 g/ cm (e.g., [1, 2]). Vesta is believed to be a dry, differentiated proto-planet with an iron core of about 220 km in diameter, a mantle with diogenite compositions and an igneous crust [1, 3, 4]. Asteroid Vesta is a fully differentiated planetary body with a complex topography [2] and a multifaceted morphology including impact basins, various forms of impact craters, large troughs extending around the equatorial region, enigmatic dark material, mass wasting features and surface alteration processes [2, 5, 6]. Vesta's topography reveals extreme height differences resulting in steep slopes, locally exceeding 40° [2, 7, 8]. Those steep slopes result in craters with an unusual asymmetrical shape, where a sharp crater rim exists on the uphill side, and a subdued rim on the downhill side [7]. Impact craters on Vesta range from fresh to highly degraded, suggesting an intensive cratering history [2, 5] similar to the Moon. Vesta is believed to be the host body of HED meteorites (Howardite-Eucrite-Diogenite) (e.g., [9, 10]). The vestan surface is mainly composed of Howardite material with localized enrichments of Eucrite and Diogenite [11, 12]. The surface material consists of thick (100 meters to a few kilometers), multilayered sheets of regolith with different albedos, formed by the accumulation of ejecta

from numerous impacts that have resurfaced Vesta over time [2, 13].

The dwarf planet Ceres is the largest object in the asteroid belt with a diameter of 940 km, a mean density of 2.162 ± 0.008 g/cm and a mass of 9.3835 x 1020 kg. Ceres is

Ceres as Revealed by Dawn

floor-fractured craters are only visible on Ceres.
