The large-scale troughs on Asteroid 4 Vesta are opening-mode fractures

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Authors

Hiu Ching Jupiter Cheng, Christian Klimczak

Abstract

The Dawn mission at Asteroid 4 Vesta revealed two sets of enormous linear structures. Both sets are troughs—linear, negative-relief landforms—with one spanning around two-thirds of the equator and the other set located in the northern hemisphere. Previous work evaluated the shapes of the troughs and interpreted them to be analogous to grabens, which are landforms caused by faulting; however, an origin from opening-mode fracture origin was heretofore not considered. To distinguish between those origins, we investigate the map patterns, cross-sectional geometries, and variations of relief and width along the length of these troughs. Both relief and width are meaningful measurands that directly relate to the vertical displacement of faults or aperture of opening-mode fractures, respectively, and thus their variations along the structures may reveal differences in fracturing behavior. We map all major troughs on Vesta, including four equatorial and two northern troughs, and no map patterns diagnostic for faulting were identified. The troughs are bounded by scalloped rims and mainly show V- and bowl shapes in cross-section. Assessment of the variation of reliefs of the two opposing trough-bounding scarps reveals that the relief maxima for each of the investigated troughs are located off-center and at different locations along the trough they bound. In contrast, we find that both the individual and cumulative variations in trough width have their maxima near the center of the trough. These map patterns and geomorphologic characteristics are largely inconsistent with the mechanics of graben formation but instead point to an opening-mode fracture origin. In addition, our calculations of lithospheric strength evolution and predicted fracturing behavior reveal that Vesta’s lithosphere has been dominated by a thick brittle portion throughout its history. Solutions to the Coulomb criterion considering a range of strengths properties of intact to fractured basaltic materials are in support of jointing as the major fracturing mode in at least the upper ~14 km of Vesta’s lithosphere.

DOI

https://doi.org/10.31223/X51G6T

Subjects

Physical Sciences and Mathematics

Keywords

normal faulting, Vesta, normal faulting, opening-mode fracture, Vesta, opening-mode fracture, asteroids

Dates

Published: 2020-10-27 13:59

Last Updated: 2020-10-27 20:59

License

CC BY Attribution 4.0 International

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