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Tectonic Features Revealed in MESSENGER Images Detailed Within Mariner 10 Stereo Topography

Introduction: The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission [1] has completed two encounters with Mercury. The MESSENGER spacecraft imaged some of the same areas of the surface as Mariner 10 with better lighting conditions for the identification of morphologic features [1]. Previously unrecognized tectonic landforms were revealed in MESSENGER images within areas imaged by Mariner 10 [2,3]. Some of these tectonic landforms are recognizable in Mariner 10-derived stereo topography. We present topographic data for some newly identified tectonic features within an area of the Michelangelo quadrangle. Methods and Data: Images from the Mariner 10 mission and MESSENGER’s first flyby were used to identify and characterize tectonic features. Topography was obtained using Mariner 10 stereo images [4] and the stereo-matching software SMTK [5]. The resulting topographic data have 1-2 km spatial resolution [5]. For the Michelangelo study area (and much of the Mariner 10 stereo topography), features at scales of less than 10 km are not resolved spatially, features at scales between 10 and 15 km are poorly resolved, and those larger than 15 km are well resolved spatially [5]. Vertical height accuracy for Mariner 10 stereo pairs has been estimated at ±0.160 km [5]. Average heights of tectonic features were determined by taking an average of >10 profiles across the feature. Observations: The study area (19o-37oS, 242o273oE) was previously imaged by Mariner 10 with less than optimal incidence angles. Many features, including craters, are difficult to recognize in the Mariner 10 image mosaic (Figure 1). Within the Mariner 10 derived topography, many additional landforms can be identified. The MESSENGER images clearly resolve previously unrecognized tectonic landforms, and the Mariner 10 topography can be used to measure the relief of these landforms. The western edge of the study area is bounded by a prominent lobate scarp (Figure 2). Lobate scarps are linear or arcuate features that are interpreted to be the surface expression of thrust faults [6-13]. The lobate scarp is ~310 km long and transects two impact craters (85 km and 100 km in diameter), suggesting that the scarp is relatively young. Mariner 10 stereo-derived topography indicates that the scarp has a maximum relief of greater than 1 km. A 165-km-long high-relief ridge is located near the southeastern margin of the study area (Figure 3). Highrelief ridges are tectonic features thought to be surface expressions of reverse faults and are generally more symmetric in cross-section than lobate scarps [10,11,13]. Topographic profiles across the high-relief ridge indicate an average relief of ~ 1 km.