{{Short description|Martian dune field}} [[File:Map of Ogygis Undae on Mars.PNG|thumb|250px|USGS map showing the location of Ogygis Undae on Mars]]
'''Ogygis Undae''' is the only named southern hemisphere [[dune field]] on [[Mars]].<ref name="USGS2">{{cite web|title=Nomenclature Search Results Target: MARS Feature Type: Unda, undae|url=https://planetarynames.wr.usgs.gov/SearchResults?target=MARS&featureType=Unda,%20undae|website=Gazetteer of Planetary Nomenclature|publisher=[[USGS]]}}</ref> It is named after one of the [[classical albedo features on Mars]], ''Ogygis Regio''.<ref name="USGS">{{cite web|title=Ogygis Undae|url=https://planetarynames.wr.usgs.gov/nomenclature/Feature/15370;jsessionid=9664E7B3222A6A4FBFDB14D84EEC5448|website=Gazetteer of Planetary Nomenclature|publisher=[[USGS]]}}</ref> Its name, which refers to [[Ogyges]], a primeval mythological ruler in [[ancient Greece]],<ref name="USGS"/> was officially approved by the [[International Astronomical Union]] (IAU) on September 17, 2015. It is situated just outside [[Argyre Planitia]], a plain located in the southern highlands of Mars.<ref name="47th Lunar and Planetary">{{cite web|author1=H. R. Charles, T. N. Titus, R. K. Hayward, and C. S. Edwards|title=Comparison of the Mineral Composition of the Sediment Found in Two Mars Dunefields: Ogygis Undae and Gale Crater|url=https://www.hou.usra.edu/meetings/lpsc2016/pdf/3006.pdf|website=47th Lunar and Planetary Science Conference (2016)|publisher=USGS}}</ref> 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).<ref name="USGS"/> They are centered at latitude −49.66°N, longitude 293.79°E (66.21°W), and extend approximately 87 km to the east and west from there.<ref name=":0">{{Cite journal|last1=Silvestro|first1=S.|last2=Di Achille|first2=G.|last3=Ori|first3=G.G.|date=September 2010|title=Dune morphology, sand transport pathways and possible source areas in east Thaumasia Region (Mars)|journal=Geomorphology|volume=121|issue=1–2|pages=84–97|doi=10.1016/j.geomorph.2009.07.019|bibcode=2010Geomo.121...84S |issn=0169-555X}}</ref><ref name="USGS"/> Ogygis Undae has an area of 1904 km<sup>2</sup>, and due to its large size is a primary subject for research on Martian [[dune]] morphology and [[sand]] composition.<ref name=":0" /><ref name="47th Lunar and Planetary"/>
== Morphology == Ogygis Undae is the final sink of an extended sand transport system that was imaged with the [[High Resolution Stereo Camera|HRSC]] camera onboard [[European Space Agency|ESA]] [[Mars Express]]. The complexity of this transport system is as extensive as some terrestrial examples. Dunes in Ogygis Undae have several morphologies including: [[Barchan|barhcan]], barchanoid, dome and [[star dune]]s. The variety of dune types indicates that they were deposited in a multimodal wind regime with different winds converging into the basin where the dunes are located, carrying sand from multiple source areas.<ref name=":0" /> The morphological complexity is mirrored by the diverse mineral composition of the dune-forming sediment.<ref name="47th Lunar and Planetary" />
== Composition == Mineral distribution across the dune fields of Ogygis Undae is non-uniform and bimodal.<ref name="47th Lunar and Planetary"/> The relative juxtaposition of the two primary grain types reveals how [[Aeolian processes]] affect the transport of sand on the surface of Mars.<ref name="47th Lunar and Planetary"/> Compositional spectra were acquired and analyzed in 2016 by USGS scientists using both the [[Thermal Emission Spectrometer]] (TES) instrument on board [[Mars Global Surveyor]] and the [[Thermal Emission Imaging System]] (THEMIS) on board the [[2001 Mars Odyssey]] spacecraft.<ref name="47th Lunar and Planetary"/><ref name="Earth and Planetary">{{cite journal|author1=Heather Charles, Timothy Titus, Rosalyn Hayward, Christopher Edwards, Caitlin Ahrens|title=Comparison of the mineral composition of the sediment found in two Mars dunefields: Ogygis Undae and Gale crater – three distinct endmembers identified|journal=Earth and Planetary Science Letters|date=15 January 2017|volume=458|pages=152–160|doi=10.1016/j.epsl.2016.10.022|bibcode=2017E&PSL.458..152C}}</ref> Other characteristics of Ogygis Undae, such as its nocturnal thermal inertia values, corroborate the finding that there is a bimodal sand-type distribution across the field.
[[Thermal emission spectroscopy]] results from the large dune field located inside [[Gale Crater]] were used as a reference for data obtained from Ogygis Undae because the features of Gale Crater were investigated extensively both by orbiting spacecraft and on site by the NASA Mars rover, ''[[Curiosity (rover)|Curiosity]]'', a part of the [[Mars Science Laboratory]] (MSL) mission.<ref name="47th Lunar and Planetary"/> Ogygis Undae differs from the Gale dune field in both sand-type composition and [[Homogeneity (physics)|homogeneity]], indicating differences in both the types of sources for these dune fields as well as the distance from their respective sand-sources.<ref name="47th Lunar and Planetary"/><ref name="Earth and Planetary"/> The USGS investigators also noted that the dunes of Ogygis Undae look similar to the dunes in [[Grand Falls, Arizona]].<ref name="47th Lunar and Planetary"/><ref name="Earth and Planetary"/>
== See also == {{Portal|Solar System}} * [[Abalos Undae]] * [[Aspledon Undae]] * [[Hagal dune field]] * [[Hyperboreae Undae]] * [[Nili Patera dune field]] * [[Olympia Undae]] * [[Siton Undae]]
== References == {{reflist|30em}}
{{Geography of Mars}}
[[Category:Dunes on Mars]] [[Category:Thaumasia quadrangle]]