Siton Undae is one of the largest and densestdune fields in the vicinity ofPlanum Boreum, theMartian northern polar ice-cap.[1] It is named after one of theclassical albedo features on Mars.[2] Its name was officially approved byIAU 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).[2] Its centre is located at latitude 75.55°N, longitude 297.28E (62.72°W), and has a diameter of 222.97 kilometres (138.55 mi).[2]
Siton Undae is part of a cluster of sand-seas (undae), which along withHyperboreae, andAbalos Undae, overlay the lowlands ofVastitas Borealis.[3] Siton Undae superposes the deepestbasin of the northern region of Mars and contains amorphoussilica-coated glass-rich dunes.[4] It is theorised that the formation of Siton Undae may have occurred during early erosion incidents of the Planum Boreum cavi unit, and thatRupes Tenuis may also have been a sand source, although it is now depleted. Other dune fields sharing the same formation history includeOlympia andAspledon Undae.[3]
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 withAbalos, and Hyperboreae Undae, is also a tributary to less dense dune fields that continue all the way to the Martianprime meridian.[1]
Spectral analysis of the dunes of the circumpolarergs, including Siton Undae, using the OMEGA instrument on board the EuropeanMars Express orbiter, indicates that 80 to 90 percent of these sands are composed ofvolcanic glass produced by eruptions of volcanoes situated in Martian glaciers. These ratios of glass and crystalline material are similar to those obtained inIceland from eruptions of volcanoes below the ice.[5] It is also theorised that significant amounts of granular glass may have been transferred to Vastitas Borealis, and Siton Undae, by catastrophic floods originating fromChryse Planitia,Valles Marineris,Juventae Chasma, and the southernAcidalia region of Mars.[5]
The dunes of Siton Undae contain amorphoussilica-coated glass-rich sand. The lack of evidence for the presence of volcanoes in the region of Planum Boreum, as well as the absence of evidence of any large-scale melt deposits due to crater impact, suggests that these silica-coated deposits may have formed by alteration of the basaltic sands through acidic action. Further, it is theorised that acidic alteration of glassy deposits may have been a common conversion mechanism on Mars, especially at high latitudes.[4]
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