Mapping of Planetary Surface Age Based on Crater Statistics Obtained by an Automatic Detection Algorithm

Abstract

ABSTRACT:The analysis of the impact crater size-frequency distribution (CSFD) is a well-established approach to the determination of the age of planetary surfaces. Classically, estimation of the CSFD is achieved by manual crater counting and size determination in spacecraft images, which, however, becomes very time-consuming for large surface areas and/or high image resolution. With increasing availability of high-resolution (nearly) global image mosaics of planetary surfaces, a variety of automated methods for the detection of craters based on image data and/or topographic data have been developed. In this contribution a template-based crater detection algorithm is used which analyses image data acquired under known illumination conditions. Its results are used to establish the CSFD for the examined area, which is then used to estimate the absolute model age of the surface. The detection threshold of the automatic crater detection algorithm is calibrated based on a region with available manually determined CSFD such that the age inferred from the manual crater counts corresponds to the age inferred from the automatic crater detection results. With this detection threshold, the automatic crater detection algorithm can be applied to a much larger surface region around the calibration area. The proposed age estimation method is demonstrated for a Kaguya Terrain Camera image mosaic of 7.4 m per pixel resolution of the floor region of the lunar crater Tsiolkovsky, which consists of dark and flat mare basalt and has an area of nearly 10,000 km 2 . The region used for calibration, for which manual crater counts are available, has an area of 100 km 2 . In order to obtain a spatially resolved age map, CSFDs and surface ages are computed for overlapping quadratic regions of about 4.4 x 4.4 km² size offset by a step width of 74 m. Our constructed surface age map of the floor of Tsiolkovsky shows age values of typically 3.2-3.3 Ga, while for small regions lower (down to 2.9 Ga) and higher (up to 3.6 Ga) age values can be observed. It is known that CSFD-derived absolute model ages can exhibit variations although the surface has a constant age. However, for four 10-20 km sized regions in the eastern part of the crater floor our map shows age values differing by several hundred Ma from the typical age of the crater floor, where the same regions are also discernible in Clementine UV/VIS color ratio image data probably due to compositional variations, such that the age differences of these four regions may be real.

Interpretation of Geological Features and Volcanic Activity in the Tsiolkovsky Region of the Moon

“…First, Boyce and Johnson [33] suggested that the age of the Tsiolkovsky basalt is 3.8 Ga. As detection data have been continuously updated, Walker et al [6] mapped 4717 impact craters in an area of 7384 km 2 and calculated the basalt age to be 3.8 Ga, i.e., Imbrian. In 1988, Tyrie et al [7] randomly selected 85 basalt regions, excluding those covered by volcanogenic and secondary impacts, and mapped 12604 impact craters with diameters ranging from 70 m to 1 km, deriving a dating result of 3.51 ± 0.1 Ga. Salih et al [8] used Kaguya Terrain Camera images with a resolution of 7.4 m per pixel to select an area of 100 km 2 on the basalt unit at the crater floor as a reference. The selected diameters of the craters ranged from 128 to 1000 m for dating, and the ages were 3.2-3.3 Ga with the youngest being 2.9 Ga and the oldest being 3.6 Ga in local areas.…”

“…Later, Walker et al [6] used lunar topographic orthophoto maps to calculate a thickness of 1.75 km and a volume of 3.6 × 10 4 km 3 for basalts in the Tsiolkovsky crater. As lunar exploration datasets are continuously updated, Tyrie et al [7] used Apollo 15 panoramic camera photographs to date the basalt via the crater size-frequency distribution method, and the result was 3.51 ± 0.1 Ga. Later, Salih et al [8] used updated Kaguya Terrain Camera (TC) data to determine that the age of the Tsiolkovsky crater floor is typically 3.2-3.3 Ga. In terms of the mineral distribution, Heather et al [9] used Clementine mosaics to determine that the central peak is feldspathic with very small, locally olivine-rich outcrops.…”