10:45 〜 12:15
[MIS20-P01] 火星高緯度域に見られるDark Dune Spotsの形成メカニズムの検証
キーワード：火星、高緯度域、Dark Dune Spot、液体塩水
In the search for living life on Mars, it is important to explore an environment where liquid water currently exists and life can survive (habitable environment). Although seasonal flow-like features called Recurring Slope Lineae (RSLs) have been identified on the slopes of Valles Marineris and other low to mid-latitude areas of Mars, some recent studies suggest that liquid waters are not likely to be involved in the RSLs (e.g., Stillman et al., 2020). On the other hand, Rivera-Valentin et al. (2020) suggest that (meta)stable brines (such as perchlorate) can form and persist on the surface of the Martian mid- to high-latitude area considering its relative humidity and temperature conditions. Given that microorganisms using perchlorate as an energy source have been identified on Earth (Logan et al., 2001), it is likely that liquid brine, if present at the high latitudes of Mars, can be a promising target in the search for living life. In the circumpolar dune field around the north polar ice cap, there is a distribution of sulfate (gypsum) that may have formed by the infiltration of liquid brine from the subglacial lake of the north polar cap (Masse et al., 2012). Therefore, in this study, we conducted a photogeological survey around the circumpolar dune field to explore the characteristic landforms formed by the involvement of liquid brine.
We visually investigated over 5,000 satellite images of HiRISE (High-Resolution Imaging Science Experiment: 1 pixel about 30 cm) obtained in the high latitude region of Mars (70° to 85°N) around the circumpolar dune field. As a result, we found a wide distribution of dark color landforms called Dark Dune Spot (DDS) appearing from spring to summer (e.g., Gánti et al., 2003) in the 75°-85°N area. We classified the DDS into two types; (1) dark color liquid flow-like structure on the dune slope region, and (2) subcircular structure in which the light color area surrounds the dark color area in the interdune region. In the dune slope region, the dark color streaks grew liquid-like and emanated during early summer, and changed to light color during mid to late summer, suggesting the salt precipitation by evaporation (Kereszturi et al., 2011). On the other hand, in the interdune region, dark color areas extended from the center to the margin during mid to late summer, suggesting that interfacial liquid may be involved (Kereszturi et al., 2012). The distribution of DDS revealed by our survey is in good agreement with the estimated distributional area of perchlorate (Li et al., 2022), suggesting that liquid brine may be involved in the DDS formation.
We also identified that there are many characteristic polygonal landforms at the bottom of the crater, called the Crater-Floor Polygon (CFP) in the 70°-75°N area. Since this polygon landform has an appearance similar to desiccation polygons found in dry lakes on Earth (El-Maarry et al., 2014), liquid water may have existed in the past. Our exploration of the high latitudes of Mars has revealed a wide distribution of landforms such as DDS and CFP, suggesting the possible involvement of liquid brine. In order to verify whether both landforms involve liquid brine, we are conducting a remote sensing survey using CRISM to see if spectral absorptions of perchlorate and chlorine are observed in the distribution areas of both landforms.
We visually investigated over 5,000 satellite images of HiRISE (High-Resolution Imaging Science Experiment: 1 pixel about 30 cm) obtained in the high latitude region of Mars (70° to 85°N) around the circumpolar dune field. As a result, we found a wide distribution of dark color landforms called Dark Dune Spot (DDS) appearing from spring to summer (e.g., Gánti et al., 2003) in the 75°-85°N area. We classified the DDS into two types; (1) dark color liquid flow-like structure on the dune slope region, and (2) subcircular structure in which the light color area surrounds the dark color area in the interdune region. In the dune slope region, the dark color streaks grew liquid-like and emanated during early summer, and changed to light color during mid to late summer, suggesting the salt precipitation by evaporation (Kereszturi et al., 2011). On the other hand, in the interdune region, dark color areas extended from the center to the margin during mid to late summer, suggesting that interfacial liquid may be involved (Kereszturi et al., 2012). The distribution of DDS revealed by our survey is in good agreement with the estimated distributional area of perchlorate (Li et al., 2022), suggesting that liquid brine may be involved in the DDS formation.
We also identified that there are many characteristic polygonal landforms at the bottom of the crater, called the Crater-Floor Polygon (CFP) in the 70°-75°N area. Since this polygon landform has an appearance similar to desiccation polygons found in dry lakes on Earth (El-Maarry et al., 2014), liquid water may have existed in the past. Our exploration of the high latitudes of Mars has revealed a wide distribution of landforms such as DDS and CFP, suggesting the possible involvement of liquid brine. In order to verify whether both landforms involve liquid brine, we are conducting a remote sensing survey using CRISM to see if spectral absorptions of perchlorate and chlorine are observed in the distribution areas of both landforms.