Introduction to a “radical” working hypothesis about a hemisphere-scale impact on Dione (Saturn)

The suspected and proved existence of subsurface oceans on various icy satellites of gas and ice giants such as Callisto, Europa, and Ganymede (Jupiter), Dione, Enceladus and Titan (Saturn), and Triton (Neptune), and the potential that such oceans may harbour life, triggered the renaissance of the research of those planetary bodies (including the ongoing Europa Clipper and JUICE missions). The centre of our research is Dione and its surface characteristics, especially with the focus on the possible relationship between the distribution of certain size craters, linear features and resurfacing processes. The pivot of the study is the region, located westward from the Eurotas and Palatine chasmata spreading approximately between latitude 50° and -50° and longitude -100° to 60° (positive East), roughly at the “transitional hemisphere” between the trailing and leading hemisphere of the moon. The studied area is defined as Intermediate Cratered Terrain, and referred as a region, which was resurfaced at some point during the early history of Dione by a still unknown process, which erased some early generation craters. This study introduces a “radical” working theory about a giant, most likely low-angle impact on the surface of Dione around 4 Ga ago, contributing to the resurfacing of the terrain. Such impact might result in the asymmetrical (“half-ring like”) distribution of secondary craters, observed in the area (i), and the formation of some early component of the Fault Terrain by the dilatation stress field during the modification phase of the impact, and/or later, during the isostatic relaxation of the surface (ii). Along surficial features, the possible formation of a unique Saturn-orbiting impactor population out of the ejectiles (or alternatively, as a “chicken and egg problem”, they might be the source of the impactor) (iii), and the very theoretical formation of the Trojan moon Helene (Dione B) following the accretion of the ejectiles (iv), might be also the results of the hemisphere-scale impact.