Ogygis Undae

USGS map showing the location of Ogygis Undae on Mars

Ogygis Undae is the only named southern hemisphere dune field on Mars.[1] It is named after one of the classical albedo features on Mars: Ogygis Regio.[2] Its name was officially approved by the International Astronomical Union (IAU) on 17 September 2015. Its name is Greek,[2] and derives from the name of Ogyges, a primeval mythological ruler in ancient Greece. The dunes of Ogygis Undae extend from latitude −49.94°N to −49.37°N and from longitude 292.64°E to 294.93°E (65.07°W – 67.36°W).[2] Its centre is located at latitude −49.66°N, longitude 293.79°E (66.21°W), and has a diameter of 87.7 km.[3][2] It is situated just outside Argyre Planitia, a plain located in the southern highlands of Mars.[4] Ogygis Undae has an area of 1904 km2, and, because to its large size, it is considered to be an excellent field on which research on dune morphology and sand composition, using data which has been gathered by the various instruments onboard robotic spacecraft sent by NASA and ESA to Mars.[3][4]

Morphological investigation

Ogygis Undae is the final sink of an extended sand transport system that was studied by means of the HRSC camera onboard on the ESA Mars Express. The complexity of the transport system can be comparable with some terrestrial examples. Dunes in Ogygis Undae have a variety of morphologies including barhcan, barchanoid, dome and star dunes. Interestingly, the different dune types indicate they were deposited in a multimodal wind regime with different winds converging into the basin where the dunes are located and bringing sand from different source areas.[3] Such a morphological complexity is mirrored by the complex mineral composition of the dune-forming sediment.[4]

Compositional investigation

The mineral content analysis of the dunes of Ogygis Undae points to a non-uniform mineral distribution across the dune field. This non-uniform distribution is also called bimodal, since it refers to two different sand types.[4] The bimodal composition is interesting to scientists because it provides an idea as to how Aeolian processes affect the transport of sand on the surface of Mars.[4] A 2016 study by USGS scientists, used the Thermal Emission Spectrometer (TES) instrument on board Mars Global Surveyor, and the Thermal Emission Imaging System (THEMIS) onboard the 2001 Mars Odyssey spacecraft, to obtain composition spectra of the Ogygis sand dunes.[4][5]

The thermal emission spectroscopy investigation results of Ogygis Undae were compared to those obtained for the large dune field located inside Gale crater. The Gale crater results were used as a reference for comparison for the Ogygis investigation, because the dune field inside Gale crater was investigated extensively both by orbiting spacecraft and on site by the NASA Mars rover, Curiosity, a part of the Mars Science Laboratory (MSL) mission.[4] Other characteristics of Ogygis Undae, such as measurements of its thermal inertia values during the night, also point to bimodal sand-type variation across the field. Ogygis Undae differed from the dune field located inside Gale crater in both sand-type composition and homogeneity, indicating differences in both the types of sources for these dune fields as well as their distance from their respective sand-sources.[4][5] The USGS investigators concluded that Ogygis Unday may exhibit bimodal distribution, and that its dunes look similar to the dunes in Grand Falls, Arizona.[4][5]

See also

References

  1. ↑ "Nomenclature Search Results Target: MARS Feature Type: Unda, undae". Gazetteer of Planetary Nomenclature. USGS.
  2. 1 2 3 4 "Ogygis Undae". Gazetteer of Planetary Nomenclature. USGS.
  3. 1 2 3 Silvestro, S.; Di Achille, G.; Ori, G.G. (2010-09). "Dune morphology, sand transport pathways and possible source areas in east Thaumasia Region (Mars)". Geomorphology. 121 (1–2): 84–97. doi:10.1016/j.geomorph.2009.07.019. ISSN 0169-555X. Check date values in: |date= (help)
  4. 1 2 3 4 5 6 7 8 9 H. R. Charles, T. N. Titus, R. K. Hayward, and C. S. Edwards. "Comparison of the Mineral Composition of the Sediment Found in Two Mars Dunefields: Ogygis Undae and Gale Crater" (PDF). 47th Lunar and Planetary Science Conference (2016). USGS.
  5. 1 2 3 Heather Charles, Timothy Titus, Rosalyn Hayward, Christopher Edwards, Caitlin Ahrens (15 January 2017). "Comparison of the mineral composition of the sediment found in two Mars dunefields: Ogygis Undae and Gale crater – three distinct endmembers identified". Earth and Planetary Science Letters. 458: 152–160. Bibcode:2017E&PSL.458..152C. doi:10.1016/j.epsl.2016.10.022.
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