Evidence and concerns about a latent, embryonic phase tectonic evolution and the existence of the young subsurface ocean on Mimas

Abstract

The icy moons of outer Solar system gas and ice giants have been in the spotlight of scientific and common interest because of the possibility of a subsurface ocean hidden under their ice shells, which may harbor extraterrestrial life. The patterns of various lineaments on the surface of icy satellites may indicate active tectonic processes and the interaction between the surface and the subsurface ocean, which allows material transport toward the habitat of putative alien life. In the case of Mimas, one of the moons of Saturn, new models challenge the long-standing conclusion about the satellite being an inactive snowball, suggesting the existence of a young ocean hiding under its ice shell. Unfortunately, no observable evidence has been found implying ongoing or probably already stopped tectonic activity and the theoretical subsurface ocean. Here, we present the first structural geological map of the icy satellite, with the signs of various tectonic features, along with a simple crosscutting chronology of lineaments formation. In accordance with the theoretical young age of the subsurface ocean, the observed phenomena are described as putative lineaments, ridges, and troughs. Such simple tectonic features are identified as young compared to complex structures, such as bands appearing on other satellites. The pattern of the linear features seems to overlap with the allocation of various modeled global nonlinear tidal dissipation patterns. In such a way, it may indicate the possible existence of the theoretical subsurface stealth ocean. With such an evolving young subsurface ocean and the barely recognizable pattern of simple lineaments, Mimas may represent a newly recognized group of icy satellites showing the early, latent, embryonic phase of tectonic activity. In contrast, the overlapping and crosscutting relations between craters and the observed features may raise some concerns about the “recent” formation of such linear features, indicating possibly long-time dormant or already stopped tectonic processes at the very early, embryonic phase of lineament formation billions of years ago. Despite the possible additional triggers of tectonic processes on icy satellites (e.g., surface crust mobility by plastic subsurface deformation), the presented geological investigation brought a new angle and additional evidence about a possible stealth ocean hiding under the crater-covered surface of Mimas, regardless of its geological age and recent state of evolution. Undoubtedly, the results and the raised concerns will trigger more intense investigations on Mimas and other, similar icy satellites in the Solar system.