Siton Undae

{{Short description|Martian dune field}}

{{use dmy dates|date=August 2017}}

File:Distribution of dune fields in the Planum Boreum region.PNG map showing the density distribution of dune fields in the Planum Boreum region. The grey regions are lower density fields. The four densest dune fields are shown in black. The prime meridian is at the bottom of the map. Siton Undae is shown on the southernmost black patch left, between longitude 291.38°E to 301.4°E (43.98°W – 57.08°W).]]

Siton Undae is one of the largest and densest dune fields in the vicinity of Planum Boreum, the Martian northern polar ice-cap.{{cite journal|author1=K. L. Tanaka, R. K. Hayward|title=MARS' NORTH CIRCUM-POLAR DUNES: DISTRIBUTION, SOURCES, AND MIGRATION HISTORY.|url=http://www.lpi.usra.edu/meetings/dunes2008/pdf/7012.pdf|publisher=Planetary Dunes Workshop: A Record of Climate Change (2008)}} It is named after one of the classical albedo features on Mars.{{cite web|title=Siton Undae|url=https://planetarynames.wr.usgs.gov/Feature/14280?__fsk=-1185990397|website=Gazetteer of Planetary Nomenclature|publisher=USGS}} Its name was officially approved by IAU on 20 March 2007. It extends from latitude 73.79°N to 77.5°N and from longitude 291.38°E to 301.4°E (43.98°W – 57.08°W). Its centre is located at latitude 75.55°N, longitude 297.28E (62.72°W), and has a diameter of {{convert|222.97|km}}.

Siton Undae is part of a cluster of sand-seas (undae), which along with Hyperboreae, and Abalos Undae, overlay the lowlands of Vastitas Borealis.{{cite journal|author1=Kenneth L. Tanaka, J. Alexis P. Rodriguez, James A. Skinner Jr., Mary C. Bourke, Corey M. Fortezzo, Kenneth E. Herkenhoff, Eric J. Kolb, Chris H. Okubo|title=North polar region of Mars: Advances in stratigraphy, structure, and erosional modification|journal=Icarus|date=28 February 2008|volume=196|issue=2|pages=318–358|doi=10.1016/j.icarus.2008.01.021|url=https://www.researchgate.net/publication/235137809|access-date=25 August 2017|ref=YICAR 8602|bibcode=2008Icar..196..318T}} Siton Undae superposes the deepest basin of the northern region of Mars and contains amorphous silica-coated glass-rich dunes.{{cite journal|author1=Horgan, B.; Bell, J. F.|title=Acid Alteration of Glass-Bearing Materials: Formation of a Major Martian Surface Type|journal=AGU Fall Meeting Abstracts |date=December 2009|volume=2009 |publisher=American Geophysical Union, Fall Meeting 2009, abstract #P13C-07|bibcode=2009AGUFM.P13C..07H}} It is theorised that the formation of Siton Undae may have occurred during early erosion incidents of the Planum Boreum cavi unit, and that Rupes Tenuis may also have been a sand source, although it is now depleted. Other dune fields sharing the same formation history include Olympia and Aspledon Undae.

Siton Undae is the southernmost of the densest northern circumpolar dune fields and its presence indicates effective sand transport and accumulation from sand sources to the north and west. Siton Undae, along with Abalos, and Hyperboreae Undae, is also a tributary to less dense dune fields that continue all the way to the Martian prime meridian.