HIGH-RESOLUTION MAPPING OF POLYGONS IN UTOPIA PLANITIA, MARS

Polygonal fractures of all scales have been observed in Utopia Planitia. Polygons at the Viking 2 Lander site are <10 m in diameter and their component troughs are ~1-2 m wide. High-resolution Viking Orbiter images show polygons ranging from 50-300 m in diameter with bounding troughs generally 4-10 m in width. Also evident in the Viking Orbiter images are 3-30 km diameter polygons with 200-800 wide troughs. Many researchers have classified these different scales of polygonal features. Generally, small-scale polygons have diameters <20 m, middle-sized are 100-300 m and giant polygons are 3-30 km.

A new evaluation of the polygons in Utopia Planitia is performed. Their locations are mapped and their topography and morphology are reexamined using newer, higher-resolution data sets. Past evaluations utilized Viking imagery, which is best displayed across southern flank of the Utopia basin. However, polar surface processes kept the northern polygons from a regional in-depth examination. THEMIS has more adequately covered the northern polygonal terrains and so a mosaic of THEMIS images of the Utopia basin is used as a base map.

A noticeable difference is observed between polygons to the south and north of the Utopia Basin. The southern polygons are 5-30 km in diameter, are irregularly shaped and not completely closed (the troughs do not always meet). Those closer to the center of the basin have steep-sided and deep bounding troughs,while those farther away appear subdued. The northern polygons tend to be smaller (1-5 km diameters), more regular in shape and completely closed. Smaller polygons can be observed nesting inside the larger northern polygons. Mapping of these different types of giant polygons will enable us to better evaluate the models of their formation.