The Hagal dune field. Image was taken on 6 February 2016 at 15:16 local Mars time.[1][2]
Hagal is the informal name of a dune field on Mars located below the north pole of Mars.[3][4] Its name derives from the sand dunes in Frank Herbert's novel Dune and the fictional planet Hagal.[4] It is located at coordinates 78.0° N latitude, 84.0° E longitude, and consists of linear and round dunes with a southeast slipface orientation.[4] It was one of the dune formations targeted for imaging by the HiRISE camera, on board the Mars Reconnaissance Orbiter, at the rate of one image every six weeks. in the third year (MY31–Mars Year 31)[5] of its seasonal expedition.[4] It is also known as the "Martian Morse Code" due to the linear and rounded formations of its dunes, which have the appearance of dots and dashes.[3][1][6][7]
Formation
Detail of the dots and dashes of the dunes on 6 February 2016, at 15:16 local Mars time.[1]
Although normally it is possible to obtain information about the wind direction from the orientation and form of sand dunes, the complexity of shapes of the Hagal dunes makes it difficult to determine the direction of the forming winds. In the case of the Hagal dunes, it is theorised that a local circular crater, probably formed due to meteorite impact and filled with sand, has decreased the quantity of dune-forming sand; this, in turn, impacted the local topography, causing a change in wind patterns.[3][1]
NASA video clip about the Martian Morse Code
The linear dunes (dashes) were formed through the action of bidirectional winds, acting perpendicular to the line of the sand dune, causing a funneling effect directing the sand to accumulate along the linear axis of the dune. The round-shaped dunes (dots) were formed when the winds that caused the linearly-shaped accumulations were interrupted. The round dunes are classified as "barchanoid dunes". However, the exact mechanism of either formation is still unknown and this is the reason the area was chosen for imaging by the HiRISE mission.[1]
Veronica Bray, HiRISE camera targeting specialist, commented that there are similarly shaped dunes in other locations on Mars, but the Hagal field provides better images of these shapes due to the uncommon characteristics of its topography. Bray also decoded the "Morse Code" of a formation as "NEE NED ZB 6TNN DEIBEDH SIEFI EBEEE SSIEI ESEE SEEE !!".[8][9]
^ abcdC.J. Hansen; S. Byrne; G. Portyankina; M. Bourke; C. Dundas; A. McEwen; M. Mellon; A. Pommerol; N. Thomas (2013). "Observations of the northern seasonal polar cap on Mars: I. Spring sublimation activity and processes"(PDF). Icarus (225): 881–897. Retrieved 19 July 2017. Please see note at Table 1 page 883: Table 1 Sites imaged systematically by HiRISE in study year 3 (MY31) of seasonal campaign. The names are informal, some based on the sand dunes in the science fiction book Dune.
^Colin M. Dundas; Shane Byrne; Alfred S. McEwen; Michael T. Mellon; Megan R. Kennedy; Ingrid J. Daubar; Lee Saper (27 January 2014). "HiRISE observations of new impact craters exposing Martian ground ice". Journal of Geophysical Research. 119 (1): 109. Bibcode:2014JGRE..119..109D. doi:10.1002/2013JE004482. Six sites were discovered in the northern summer of Mars Year 29 (MY29), seven in MY30, and seven in MY31. (MY refers to the Mars calendar of Clancy et al. [2000], and this notation will be used throughout this paper; years begin at LS = 0°, the beginning of northern spring. MY32 began on 31 July 2013.)
