11:45 〜 12:00
[PPS06-10] Estimating the subsurface ice distribution and surface environment on present-day Mars: Insights from a terrestrial analog study
★Invited Papers
キーワード：火星、表層環境、地下氷、地球アナログ
Mars is considered to have had a thick atmosphere and warm and humid environment conducive to extraterrestrial life about 3.8 billion years ago. However, the present-day Mars has only a thin atmosphere and extremely cold and dry environment. Most of the early liquid water dissipated into space about 3.5 billion years ago, although a significant amount of H2O water seems to remain stored as ice in the polar cap and shallow subsurface at mid-to-high latitudes (Head et al., 2003). In addition, it has been suggested that salt brine may also exist in liquid form at high latitudes today (Rivera-Valentin et al., 2020), and that it may be possible for extant organisms to exist in relation to the brine. Therefore, Mars is an extraterrestrial planet for which the persistence and evolution of habitable environments can be examined.
In this study, we focus on periglacial landforms (thermal contraction polygons, pingos, and brain terrains) formed by the presence of subsurface ice, and desiccation polygons formed by surface water evaporation. This is to gain insights about the surface and shallow subsurface environment on present-day Mars. Thermal contraction polygons and pingos are known to develop in the permafrost regions of the Earth (e.g., Siberia, Alaska, Arctic Archipelago, and Antarctica). On the other hand, desiccation polygons develop in salt lake environments of desertic arid zones. For examining the surface environment and estimate the subsurface ice distribution of Mars, we chose Mongolia, where the boundary between the permafrost and desert belts is located, as an important terrestrial analog site. We explored the distribution of the periglacial and desiccation landforms in the country.
As a result of our field survey conducted in June-July 2023, periglacial landforms similar to those found in mid-latitude regions of Mars were observed in northern Mongolia, where a continuous permafrost is distributed. Brain terrains, which were thought to be unique to Mars, were also found in several places in northern Mongolia. In addition, we found 'relict' thermal contraction polygons in the southern isolated permafrost zone, which is thought to have been formed by the disappearance of subsurface ice that existed earlier. In addition, we found relict desiccation polygons, and they are distributed over a 50 km wide swath in the northern margin of Gobi Desert in southern Mongolia, indicating the possibility of past existence of a giant salt lake. We plan to continue our exploration of terrestrial analog sites using ground-penetrating radar. Based on the terrestrial analog study, we intend to reconstruct the evolution of the surface and shallow subsurface environment in the mid-latitude region of Mars since recent past.
In this study, we focus on periglacial landforms (thermal contraction polygons, pingos, and brain terrains) formed by the presence of subsurface ice, and desiccation polygons formed by surface water evaporation. This is to gain insights about the surface and shallow subsurface environment on present-day Mars. Thermal contraction polygons and pingos are known to develop in the permafrost regions of the Earth (e.g., Siberia, Alaska, Arctic Archipelago, and Antarctica). On the other hand, desiccation polygons develop in salt lake environments of desertic arid zones. For examining the surface environment and estimate the subsurface ice distribution of Mars, we chose Mongolia, where the boundary between the permafrost and desert belts is located, as an important terrestrial analog site. We explored the distribution of the periglacial and desiccation landforms in the country.
As a result of our field survey conducted in June-July 2023, periglacial landforms similar to those found in mid-latitude regions of Mars were observed in northern Mongolia, where a continuous permafrost is distributed. Brain terrains, which were thought to be unique to Mars, were also found in several places in northern Mongolia. In addition, we found 'relict' thermal contraction polygons in the southern isolated permafrost zone, which is thought to have been formed by the disappearance of subsurface ice that existed earlier. In addition, we found relict desiccation polygons, and they are distributed over a 50 km wide swath in the northern margin of Gobi Desert in southern Mongolia, indicating the possibility of past existence of a giant salt lake. We plan to continue our exploration of terrestrial analog sites using ground-penetrating radar. Based on the terrestrial analog study, we intend to reconstruct the evolution of the surface and shallow subsurface environment in the mid-latitude region of Mars since recent past.