11:15 〜 11:30
[PPS05-08] The distribution of periglacial landforms in the northern mid-latitude of Mars
キーワード：火星、周氷河地形、火星の地下氷、ポリゴン
Human mission to Mars in the 2040s is planned by NASA's Artemis program requiring an estimation of the subsurface ice distribution in the mid-latitude of potential landing sites, which could serve as water resources. Through the integration of orbital datasets (Radar data analysis, water equivalent hydrogen detection) in conjunction with the glacial landform distribution, the Subsurface Water Ice Mapping (SWIM) project also aims to reconstruct the distribution of subsurface ice (Morgan et al., 2021). However, since the SWIM project rely mainly on the glacial landforms which are interpreted to have formed during the past high-obliquity periods (Head et al., 2003; Levy et al., 2010), it may not reflect the present subsurface ice distribution. Therefore, the distribution of periglacial landforms is thought to better reflect the existing subsurface ice.
In this study, we investigated the distribution of three hypothesized periglacial landforms (i.e., thermal contraction polygons, fractured mounds, brain terrain) that could provide evidence for subsurface ice in the mid-latitude of Mars (30-42°N) using HiRISE (High-Resolution Imaging Science Experiment) images. We classified seven types of thermal contraction polygons according to the shape, such as high-centered polygon [HCP], low-centered polygon [LCP], mixed polygon [MP], polygon in scalloped depression [PSD], Unintelligible polygon [UP], Desiccation polygon [DP], Irregular polygon [IP]. Our investigation result reveals that three periglacial landforms (thermal contraction polygons, fractured mounds, and brain terrains) have nearly similar distribution patterns, and exhibit a longitudinally heterogeneous pattern: predominant in the Eastern Hemisphere and less prominent in the Western Hemisphere. The distribution of the periglacial landforms is consistent with the reconstructed distribution of the annual water ice budget obtained by the Mars GCM (Forget et al., 1999; Madeleine et al., 2009), supporting the notion that their distribution reflects the subsurface ice distribution.
The thermal contraction polygons show rather different distribution patterns for each type. HCP is the most abundant type in the searched area (between 30°N to 42°N), while MP is predominantly observed in the 60°-100°E region. The MP type is a large-sized polygon of about 100 m in diameter containing smaller polygons of 5 to 20 m in diameter and without cracks at the edges. The small polygons without cracks at the edges have likely formed as sand wedge polygons, and their distribution is consistent with the reconstruction from the Mars GCM indicating that a plenty of subsurface ice existed in the past but has been degraded toward the present.
In this study, we investigated the distribution of three hypothesized periglacial landforms (i.e., thermal contraction polygons, fractured mounds, brain terrain) that could provide evidence for subsurface ice in the mid-latitude of Mars (30-42°N) using HiRISE (High-Resolution Imaging Science Experiment) images. We classified seven types of thermal contraction polygons according to the shape, such as high-centered polygon [HCP], low-centered polygon [LCP], mixed polygon [MP], polygon in scalloped depression [PSD], Unintelligible polygon [UP], Desiccation polygon [DP], Irregular polygon [IP]. Our investigation result reveals that three periglacial landforms (thermal contraction polygons, fractured mounds, and brain terrains) have nearly similar distribution patterns, and exhibit a longitudinally heterogeneous pattern: predominant in the Eastern Hemisphere and less prominent in the Western Hemisphere. The distribution of the periglacial landforms is consistent with the reconstructed distribution of the annual water ice budget obtained by the Mars GCM (Forget et al., 1999; Madeleine et al., 2009), supporting the notion that their distribution reflects the subsurface ice distribution.
The thermal contraction polygons show rather different distribution patterns for each type. HCP is the most abundant type in the searched area (between 30°N to 42°N), while MP is predominantly observed in the 60°-100°E region. The MP type is a large-sized polygon of about 100 m in diameter containing smaller polygons of 5 to 20 m in diameter and without cracks at the edges. The small polygons without cracks at the edges have likely formed as sand wedge polygons, and their distribution is consistent with the reconstruction from the Mars GCM indicating that a plenty of subsurface ice existed in the past but has been degraded toward the present.