1. Estimating Grain Sizes of Martian Dune Sand: A Freeware‐Based Methodology With Initial Results.
- Author
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Burr, D. M., Nguyen, V. N. H., Gibson, T. M.‐G., and Chinchkhede, T.
- Subjects
SAND dunes ,GRAIN size ,GRAIN yields ,IMAGE databases ,SAND - Abstract
Grain sizes of Martian sand dunes are critical sedimentological data on sand provenance and transport pathways. Thermal inertia values are used to characterize the grain sizes of dune sand. Most early characterizations involved single dune fields. Recent work based on global data sets has provided more wide‐spread dune sand locations, though these data sets include the non‐sandy interdune areas. To provide a more accurate grain size characterization, we leverage a global thermal inertia data set, a global dune database and a global imaging mosaic to develop a freeware‐based methodology for deriving grain sizes. This methodology involves delineation of sand‐only areas within dune fields and collection of thermal inertia values from those areas. We consider a unimodal histogram of values with a mode <∼350 thermal inertia units (J m−2 K−1 s−1/2) to imply an effective exclusion of non‐sand surfaces. Application of this methodology to dune fields for which thermal inertia values have been previous derived shows our results fall within the envelope of those values. We apply our methodology to tropical dune fields on Mars for which Dust Cover Index data imply dust‐free surfaces. Conversion of these thermal inertia values to sand grain sizes yields a range of sand classifications of fine sand to granules. Comparison of sand size classifications with geographic location shows grain size ranges that are distinctive by location, consistent with local sourcing. This work points toward geographically diverse sand formation mechanisms yielding diverse grain sizes, while providing a freeware‐based and thus widely accessible method for expanding the derivation of these critical data. Plain Language Summary: Knowing the sizes of sand grains on Mars provides information on the history of that sand, such as where it came from and how far it has traveled to where it is now. Sand grains of different sizes respond to heat differently, with larger sand grains heating up and cooling down more slowly than smaller grains or dust. This response to heating—termed "thermal inertia"—has been used for decades to estimate the grain sizes of dune sand on Mars. However, previous methods have been focused on only a few dune fields at a time. To increase the amount of grain size data we can collect from sand dunes on Mars, we have developed a freeware‐based approach using global data sets and software that are accessible to anyone. Applying our approach to all the dunes for which grains sizes based on thermal inertia were previously derived, we show that our values are similar to those from the previous work. Applying our approach to 75 dune fields on Mars, we see different dune fields have different grain sizes, which suggests different sand formation mechanisms in these different locations. Thus, our freeware‐based approach provides an accessible opportunity to learn about sand characteristics and sand histories across Mars. Key Points: We develop and test a fully freeware‐based method for estimating grain sizes of Martian dune sand and apply it to tropical dune fieldsOur grain size values fit within the envelope of grain size values from decades of previous work, indicating the validity of our methodOur results also reveal geographic variability in grain sizes, indicating geospatial variability in sand‐forming mechanisms on Mars [ABSTRACT FROM AUTHOR]
- Published
- 2024
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