There have been several attempts to estimate water chemistry on early Mars using geochemical reaction-transport modeling. There is good evidence in the form of observable river deltas, and more recent measurements made on Mars‘ surface, that liquid water did flow on Mars billions of years ago.
To more readily constrain such claims, researchers are attempting to comprehend the sorts of water chemistry that could have created the minerals seen on Mars today, which were produced billions of years ago.
Salinity, pH, and redox states are fundamental properties that characterize natural water. These properties of surface waters on early Mars reflect palaeoenvironments and thus provide clues on the palaeoclimate and habitability.
Scientists recently constrained these properties of pore water within lacustrine sediments of Gale Crater, Mars, using smectite interlayer compositions. Regardless of formation conditions of smectite, the pore water that last interacted with the deposits was of Na-Cl type with mild salinity (~0.1–0.5 mol/kg) and circumneutral pH.
To quantitatively estimate the water chemistry of the pore water that finally interacted with the sediments, scientists used the exchangeable cation compositions of smectite’s interlayer together with the presence of secondary minerals commonly found in Yellowknife Bay.
The results show that the pore water is characterized as mildly saline, Na–Cl type water.
This suggests that these sediments formed in the presence of liquid water, which was of a pH close to that of Earth’s modern oceans.
Earth’s oceans are, of course, host to myriad forms of life, thus it seems compelling that Mars’ new surface environment was a place contemporary Earth life could have lived, but it remains a mystery as to why evidence of life on Mars is so hard to find.
The findings of this study are published in the journal Nature Communications.