Ariadnes-Gorgonum Knob Fields of North-Western Terra Sirenum, Mars

Fields of knobs and small mesas outcrop principally in five adjacent basins in northwestern Terra Sirenum (~32-43 S, 166-192 W). Several of these knob fields (the largest) have names. East to west they are: Gorgonum Chaos, Atlantis Chaos, and Ariadnes Colles. These three largest knob fields are on order of 200 km across and are roughly equant but with very irregular boundaries in plan view . There are several smaller knob fields in smaller nearby basins; some as small as 20 km across. Knob material, where unmantled, is relatively brighter than its surroundings. The largest individual knobs are almost invariably mesas with typical plan dimensions of ~10 km and relief > 200 m. Knob profiles transition from mesas to rounded mounds with decreasing size. Individual knobs range in size down to ~100 m in plan view and relief < 10 m where seen on some MOC NA images.