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Dark Streak Features in Mongolia as Terrestrial Analogues of Recurrent Slope Lineae on Mars
| Content Provider | Semantic Scholar |
|---|---|
| Author | Nakamura, Mototaka Sekine, Yoshitsugu Fukushi, Keisuke Hasebe, Nobuyuki Davaadorj, D. Takahashi, Yukihiro Hasegawa, Hiroshi Ogura, Tomoo Morida, K. |
| Copyright Year | 2019 |
| Abstract | Introduction: Recurrent Slope Lineae (RSL) are dark, narrow features that appear and lengthen on steep (~30°) slopes in warm seasons and fade in cold seasons of Mars [1,2,3]. Although the formation mechanism of RSL is still in debate, several processes have been proposed, including liquid brine flows triggered by melting of subsurface ice (wet processes) [4,5], and granular flows (dry processes) [2,6]. However, neither wet nor dry processes can explain all of the observables of RSL. In especially, the wet processes seem to be inconsistent with the absence of absorptions due to liquid water on RSL and the fact that RSL appear only on steep slopes [2]. A bottleneck that makes the formation mechanism remain unclear is that RSL have been investigated mainly through remote-sensing data of Mars. Here, we report similar dark streak features on Earth in cold, arid areas of central Mongolia. We conduct geological survey for the terrestrial RSL analogue sites to construct the high-resolution three-dimensional structure and to analyze soil samples. Based on the formation mechanism of the terrestrial RSL analogues, we discuss the formation of RSL on current Mars, especially aiming to explain the absence of absorption of liquid water and the fact that RSL appear only on steep slopes in the context of the wet processes of RSL formation. Dark streak features in Mongolia: We first searched for RSL-like dark, narrow features over Earth’s surface using Google Earth satellite images. We focused on arid or semi-arid areas because of less vegetation, which include Namib, Atacama, and Gobi deserts. Among these areas, we find RSL-like dark streak features only in cold and arid, southern part of Khangai Mountains in central Mongolia (Fig. 1), where discontinuous permafrost and underground ice melt seasonally [7]. Comparing the satellite images taken at different times, we find that dark streak features in this area show seasonal variation similar to RSL on Mars; namely, the streaks appear in summer and fade in winter. Although the slope angles of the terrestrial analogues (~10° or greater) are shallow, the observed similarities in morphology and seasonal activity (Fig. 1) suggests that the streak features in Mongolia can be promising terrestrial analogues of RSL on Mars. Geological survey & analyses: We then conducted geological survey for two sites of the terrestrial RSL analogues found in Mongolia in the end of August 2018. One (termed, the site-BH) is located at 10-km north of Bayankhongor at altitude of 2060 m from the sea level, and the other (termed, the site-GB) is located at 25-km north of Gurvanbulag at altitude of 2630 m from the sea level. Owing to high elevation of the siteGB, a mean surface temperature at the site-GB (~4oC) in the end of August was significantly lower than that at the site-BH (~10oC). At both of the sites, dark streak features were found on the slopes during the survey from visual images taken by an unmanned aerial vehicle (i.e., a drone). By analyzing the visual images taken by the drone with a software of PhotoScan, a threedimensional topographic structure was constructed at each site with a spatial/vertical resolution of 2–9 cm. A flow accumulation analysis was performed for the obtained topographic structure using a software of QGIS. In the geological survey, we measured water contents of soils on site on and outside the dark streak features. The mineralogical compositions and grain size distributions were measured for the collected soil samples. During the survey, no water flow was observed at the site-BH, whereas water flow occurred on the slopes at the site-GB possibly due to melting of underground ice (see below). Velocity, depth, and width of the water flow were also measured on site at the site-GB. The chemical composition of the collected water was measured with ICP-AES. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://www.hou.usra.edu/meetings/lpsc2019/pdf/2269.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
