Detailed mapping of perchlorate distributions with Phoenix and CRISM and evidence of modern aqueous redistribution

The 2008 Mars Phoenix lander returned evidence of small amounts of perchlorate salt in the soils at the landing site on the northern plains of Mars. Perchlorate salts are significant to our understanding of the modern Martian water cycle, because they are extremely soluble in water. Their presence at the Phoenix landing site has been interpreted to show that the Phoenix soils undergo processing by thin films of liquid water during seasonal cycles. This is an exciting process that could be occurring across the northern plains of Mars. However, is still unclear exactly how widespread perchlorate salts are and how their abundances vary spatially. This question is of particular import, because perchlorate salts are thought to form atmospherically on Mars, which would create a more or less homogeneous distribution across the surface. Dissolution and redistribution by water, on the other hand, should create a heterogeneous distribution. Perchlorate distribution, then, can be used as a marker of how recently a surface has interacted with liquid water. Here, we map variations in the abundance of perchlorate salts across the northern plains of Mars on two scales: first, a high-resolution, low-spatial scale mapping of perchlorate abundances at the Phoenix landing site, using lander data from the Surface Stereo Imager (SSI); second, a low-resolution, wide-spatial scale survey using orbital data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). To derive perchlorate abundances, we compare our CRISM and Phoenix mapping results to laboratory spectra of perchlorate and to results from mathematical modeling of perchlorate-soil mixtures.