Post by Dr. Candice Hansen and Dr. Mary Bourke,
Planetary Science Institute, Tucson, Arizona, 85705
Geography, Trinity College, Dublin, Ireland
Every year, Mars’ polar regions are covered by a seasonal layer of CO2 ice (dry ice). We are just beginning to understand the important role this volatile plays as an active agent of geomorphic change on Mars. The HiRISE camera on the Mars Reconnaissance Orbiter has been used to study sublimation activity in the spring for 3 Mars years. C hannel features often organised in radial patterns were noted and known informally as “spiders”, more formally as “araneiform terrain” (Image 1). They are tens to hundreds of m wide, with individual channels measuring several meters wide. Estimates of depth are in the order of ~ 2 m, decreasing with distance from the center of the araneform. Thin channels widen and deepen as they converge. Where they drape pre-existing topography, the channels are larger in the uphill direction suggesting they were eroded by pressurised fluid (Hansen et al, 2010).