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Recurring Slope Lineae ( Rsl ) following the 2018 Planet-encircling Dust Event ( Pede )
| Content Provider | Semantic Scholar |
|---|---|
| Author | Mcewen, Alfred S. Schafer, Ewan Sutton, S. Chojnacki, Matthew |
| Copyright Year | 2019 |
| Abstract | MRO/HiRISE has been seeing many more candidate RSL than in typical years, following the 2018 dust storm. They have been imaged at 216 unique locations during August-December of 2018, about half of them at locations where RSL have not been seen previously (Fig. 1). They are present on most steep, rocky slopes in the southern middle latitudes in southern summer of Mars Year (MY) 34, rather than ~40% as seen previously [1]. The RSL in late 2018 are present over a wider range of latitudes and slope aspect than in prior years. These RSL sites also show evidence for recent dust deposition: obscuration of relatively dark areas, overall brighter and redder surface than in prior years, and dust devil tracks. These post-PEDE RSL observations could be explained by flow of freshly-deposited dust down steep slopes [2]. If this is the case, then the otherwise puzzling recurrence and year-to-year variability of RSL activity are now explained. Fig. 1: RSL abundant after 2018 PEDE (bottom) but absent in a prior year at about the same season. Introduction: Recurring Slope Lineae (RSL) are relatively dark flows on steep slopes with low albedos (minimal dust cover), typically originating at bedrock outcrops [2, 3]. Individual linea are up to a few meters wide and up to 1.5 km long. RSL recur annually (by definition) over the same slopes. The lineae grow incrementally over a period of several months, usually during the warmest time of year for the particular latitude and slope aspect, then fade (and typically disappear) when inactive. This pattern repeats over multiple years, with varying degrees of interannual variability. They are often associated with pristine small gullies or channels that are otherwise rare on equatorial slopes. Hundreds of individual lineae may be present over a local site, and thousands in a single HiRISE image, and there are hundreds of likely RSL sites [1, 4-6]. RSL are common in the southern middle latitudes where they are most active in southern summer on equator-facing slopes, the equatorial regions where activity is usually timed to when the local slope receives the most insolation, and in Acidalia/Chryse Planitia with activity in northern spring and summer [5]. RSL are classified as “fully confirmed” when incremental or gradual growth, fading, and yearly recurrence have all been observed [4]. They are called “partially confirmed” when either incremental growth or recurrence have been observed, or “candidate” sites when they resemble RSL in single images but changes have not been observed or only fading has been seen. Post-PEDE Observations: Correlations between RSL activity and dust storms has been described by previous workers [3-5, 6-7]. In particular there seemed to be greater RSL activity in 2007 following the MY28 PEDE. However, since the unique temporal behavior of RSL had not been recognized in 2007, the HiRISE images were all targeted for other purposes, and we had no “before” images at any of these locations. The 2018 PEDE provided the opportunity to more systematically monitor RSL. In addition, HiRISE has an ongoing campaign of imaging gullies for changes [8], mostly on pole-facing slopes where RSL are not typically found. But in late 2018 we usually see RSL on the steep eastand west-facing slopes of pole-facing gullies and alcoves. We have also seen new RSL in images targeted for reasons other than monitoring slope processes. As a result, we collected a total of 260 images containing candidate RSL from August 20-December 28 of 2018, in 216 unique locations (plus 44 repeat images) (Fig. 2). The 2018 PEDE was in its decay phase by August, but dust opacities remained quite high, obscuring small-scale surface features. We did identify some RSL during this decay phase, which provided an im1376.pdf 50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132) |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://www.hou.usra.edu/meetings/lpsc2019/pdf/1376.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
