We next make several assumptions to calculate the concentration of salts that have accumulated in the soil during the Amazonian eon. We first assume that perchloric acid, sulfate aerosols, nitric acid and pernitric acid have accumulated at a uniform rate. This assumption is valid because the lack of aqueous minerals and very low weathering rates tell us the Amazonian eon on Mars has been characterized by a climate and atmosphere not greatly different from today (Bibring et al., 2006). We next assume a range of soil mixing depths so that salts are distributed throughout the soil column. According to Zent (1998), small post-Noachian impactors have churned the soil on Mars to a 1/e mixing depth of 0.51–0.85 m. Taking three e-folding depths, the range would be 1.5–2.6 m depth, with a mean ∼2 m. The last assumption we make is that the soil density is 1 g cm−3 (Moore and Jakosky, 1989). Using these assumptions, we calculate the concentrations of anions in the soil for the nominal model and report them in Table 4. These anions must be combined into salts. For perchlorate, the salts may be Mg(ClO4)2 or Ca(ClO4)2 as discussed earlier. The dominant nitrogen-bearing salt is unknown.
1/e
impactors have churned the soil on Mars
1/e mixing depth
0.51–0.85 m.
m
e-folding depths
three
three e-folding depths
depth
1.5–2.6 m
m
three e-folding depths
depth
∼2 m.
m
soil
density
1 g cm−3
g cm−3