On the cryogenic nature of the large hills of Mars

Abstract

The nature of large hills in the Martian equatorial regions like Zephyria Planum and the southern part of Elysium Planitia has not been studied, despite the fact that they have characteristic similar shapes and sharply contrast with the surrounding lava plains. The paper develops the previously proposed view on the permafrost injection nature of these formations. Morphological analysis of satellite imagery in the visible and infrared ranges of large cone-shaped and dome-shaped hills in the equatorial parts of Zephyria Planum and the southern part of Elysium Planitia gives grounds to interpret these structures as large hydrolaccoliths. Analysis of the terrain and signs of ongoing geological processes using satellite images of various years and modern views on the permafrost and subpermafrost waters of the planet confirms this interpretation. The origin of these structures is associated with temperature changes and phase transitions in the permafrost layer. It is assumed that their structure does not fundamentally differ from the terrestrial analogues like pingo, or bulgunnyakh: the core contains ice-containing permafrost and massive ice, from the surface they are covered with regolith. The differences are the significantly large dimensions of these features and the assumed hydraulic connection with the brine subpermafrost hydrosphere. Morphological signs of modern activity of some of the large hydrolaccoliths are observed, which indicates a hydraulic connection with the underlying supply reservoirs. Large hydrolaccoliths are of interest as significant reserves of water surrounded by a waterless landscape and as places to search for traces of life in ice substrates and feeding brines. Сonsidering their significant resource and scientific potential, the equatorial areas, where the described and similar features occurred, are promising as places for the first crewed missions and setting up human settlements.