New images of Mercury's surface from 210° to 290° W longitudes with implications for Mercury's global asymmetry

Abstract

Ground-based images of Mercury in the sector 210° to 290° W (70° to 150° E) longitude, a region not imaged by Mariner 10, show many impact craters and at least two large basins. A millisecond exposure method was used at the Abastumany and Skinakas Observatories. Under good atmospheric conditions enough images were obtained, that when stacked increased the signal to noise ratio, and gave rise to resolution that shows unprecedented detail of surface albedo and physical features. We discuss images of a double rimmed basin whose inner portion extends 1000 km across with a total dimension of the outer eroded rim slightly more than 2000 km (extending over 245° to 305° W (55° to 115° E) longitude and from 40° N to 20° S). This basin includes and extends west and north of the dark albedo feature known as Solitudo Criophori and was unofficially called “Skinakas” after the observatory from which it was first imaged. In this manuscript we call the feature Basin S. The inner basin extends from 263° to 287° W (73° to 97° E) and from about 30° N to 5° S. Some regions within the basin have eroded circular rims that lack rayed structure or evidence of ejecta material. These images also show large basins, unusual clusters of circular rimmed features, and darker albedo material between 210° and 330° W (30° to 150° E) longitude. Implications of the huge basin for the geophysics of Mercury are discussed. Many well defined impact craters have also been imaged. An attempt has been made to restore information about relief of the 210° to 290° W (70° to 150° E) longitude sector. In addition, regions on the order of 10° of latitude and 10° of longitude have been examined and reveal rayed craters in comparable detail to the Arecibo radar imaging. Images at the same location where radar backscatter has indicated infilling of craters by volatiles or some other highly coherent backscattering material are also shown.