How long was Meridiani Planum wet? Applying a jarosite stopwatch to determine the duration of aqueous diagenesis

摘要

Jarosite dissolution rates can be used to determine the duration of water at Meridiani Planum and other environments containing this ephemeral, metastable ferric sulfate salt. The maximum duration of aqueous fluids in the region is calculated based on the dissolution rate of jarosite under varying temperature and ionic strength conditions. Jarosite lifetimes predicted in this study range from 1.5 a in warm dilute environments to 100 ka in NaCl-saturated brines at 250 K. The preservation of jarosite within rocks at Meridiani Planum requires that aqueous fluids were active over a small fraction of the billions of years since jarosite formed or was deposited in the region, limiting the probability of life being established in such a temporally restricted system. In addition, water-related features such as hematite spherules and crystal molds must have formed relatively quickly during this geologically short period of aqueous diagenesis.