Introduction: The geologic mapping of Vesta
Introduction
In July 2011 NASA’s Dawn spacecraft arrived in orbit around the main belt asteroid (4) Vesta, beginning a more than year-long orbital study of this unique protoplanet (Russell and Raymond, 2011, Russell et al., 2012). The Dawn spacecraft studied Vesta with three instruments: a German-built Framing Camera (FC: Sierks et al., 2011), an Italian-built visible and infrared spectrometer (VIR: De Sanctis et al., 2011), and an American-built gamma ray and neutron detector (GRaND: Prettyman et al., 2011). The spacecraft’s radio communications system also conducted a gravity experiment (Raymond et al., 2013). A geologic mapping campaign was developed as part of the Nominal Mission to provide a systematic, cartography-based initial characterization of the global and regional geology of Vesta. The intent of the geologic mapping campaign was twofold: (1) provide geologic and stratigraphic context for analysis by the Science Team, and (2) inform the broader science community about the evolving perspectives regarding the geology of Vesta during the mission timeline. The purpose of this introductory paper is to highlight major aspects of the geologic mapping campaign for Vesta, while simultaneously reducing the amount of replicated information in each of the papers in this Special Issue/Section. Herein we include a brief summary of pre-Dawn knowledge of physiography and geologic character of Vesta, discuss the goals of the mapping effort, and summarize the basemap and ancillary materials as well as the methodologies used in the Vesta quadrangle-based mapping effort. We then present the global geologic context for the quadrangle mapping effort, discuss the challenges that arose in the mapping of a relatively small airless body like Vesta, and briefly describe the content of the other papers in this Special Issue. We conclude with a list of lessons learned that future mission teams should review when designing a geologic mapping program to aid in the analysis of data during the nominal mission. The goal of this paper is not to provide a full document of background elements (these are described in part in previously published papers) but to help establish a coherent context for the topical geologic mapping papers that follow. Information relevant to mapping efforts or interpreted geology of specific quadrangles is presented directly in the following papers, as necessary.
Section snippets
Background: the importance of Vesta
The inner Main Belt Asteroid (4) Vesta was discovered by H.W. Olbers in 1807 (see review by Pilcher, 1979) and orbits the Sun at a mean heliocentric distance of 2.36 astronomical units (AU) with an eccentricity of 0.097 (Williams, 1989). Hubble Space Telescope (HST) observations showed that Vesta is a triaxial ellipsoid with a flattened south polar region (Thomas et al., 1997a). Subsequent measurements by the Dawn spacecraft show that Vesta has radii of 286.3 km × 278.6 km × 223.2 km (±0.1 km), a mean
Geologic mapping of Vesta
Geologic maps serve as tools to understand the evolution of the terrestrial planets and satellites (Carr et al., 1976, Carr et al., 1984, Greeley and Carr, 1976, Wilhelms, 1990, Hansen, 2000, Tanaka et al., 2010). The overarching goal of geologic maps is to place observations of surface features into their stratigraphic context to develop a sequence of events for the evolution of planetary surfaces (see Carr et al., 1976). Relative stratigraphic dating and estimation of ages from impact crater
Overview of papers in this Special Issue/Section
This Special Issue/Section contains papers that address specific science topics regarding Vesta geology, in which the quadrangle maps served as tools to address the science questions. There is not one paper for each of the 15 Vesta quadrangles; rather, quadrangle maps were combined where appropriate to better address science questions. For Vesta’s northern hemisphere, three papers explore various aspects of the geology. Ruesch et al. (2014) have combined quadrangles Av-1 (Albana), Av-2
Lessons learned
In this section we note the specific lessons learned from our quadrangle-based geologic mapping effort (Table 3a) and make specific recommendations for future missions wanting to conduct a geologic mapping program during their nominal mission (Table 3b).
Although not initially driven by specific science goals for each quadrangle, the quadrangle-based geologic mapping approach that we used throughout the nominal mission provided the team with initial descriptions and interpretations of regional
Acknowledgments
We thank reviewers James Skinner and Sharon Purdy Wilson and Consulting Editor Peter Thomas for helpful reviews. We thank James Skinner, Trent Hare and Ken Tanaka for helpful discussions regarding the initiation of the Vesta mapping program. We thank Carle Pieters, Ralf Jaumann, Chris Russell, Carol Raymond, and all the members of the Dawn instrument, Science, and Flight Teams for their work operating the spacecraft and returning and processing data of Vesta. DAW, RAY, and WBG were funded from
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2021, Planetary and Space ScienceCitation Excerpt :Other geologic maps have been published in journals with map supplements. Some of these maps have been created systematically under coordinated guidance, such as the Geologic Maps of Vesta based on 15 individual quadrangles and published individually as well as unified with a global scale of 1:1,000,000 (e.g., Yingst et al., 2014; Williams et al., 2014, and references cited therein), or the Geologic Maps of Ceres based on 15 individual quadrangles published individually at map scales of 1:500,000 and 1:1,000,000 (Williams et al., 2018). These efforts are still ongoing, and a clean map compilation is expected within the next few years.
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