ABSTRACT
The Mars Sample Return mission intends to retrieve a sealed collection of rocks, regolith, and atmosphere sampled from Jezero Crater, Mars, by the NASA Perseverance rover mission. For all life-related research, it is necessary to evaluate water availability in the samples and on Mars. Within the first Martian year, Perseverance has acquired an estimated total mass of 355 g of rocks and regolith, and 38 µmoles of Martian atmospheric gas. Using in-situ observations acquired by the Perseverance rover, we show that the present-day environmental conditions at Jezero allow for the hydration of sulfates, chlorides, and perchlorates and the occasional formation of frost as well as a diurnal atmospheric-surface water exchange of 0.5-10 g water per m2 (assuming a well-mixed atmosphere). At night, when the temperature drops below 190 K, the surface water activity can exceed 0.5, the lowest limit for cell reproduction. During the day, when the temperature is above the cell replication limit of 245 K, water activity is less than 0.02. The environmental conditions at the surface of Jezero Crater, where these samples were acquired, are incompatible with the cell replication limits currently known on Earth.
ABSTRACT
RATIONALE: The classic CO2 -H2 O equilibration method is a very popular technique for the measurement of the oxygen isotope composition of aqueous samples in stable isotope geochemistry. This study examined whether enzymatically controlled CO2 -H2 O equilibration by carbonic anhydrase (CA) could reduce the time for oxygen isotope equilibrium between CO2 and H2 O at 25°C. METHODS: Four types of aqueous samples containing CA were equilibrated with CO2 gases using a continuous flow isotope ratio mass spectrometer equipped with an automated gas sample collection device. We examined the effect of CA concentration in an aqueous sample, the influence of drying technique for the preparation of sample vials containing dried CA, the age of CA stock solution, and the ionic strength and the oxygen isotope composition of aqueous samples. RESULTS: CA rapidly catalyzed the oxygen isotope exchange between CO2 and H2 O and was unaffected by drying technique or stock solution age. Compared with aqueous samples with no CA or 0.2 µmolal CA, samples containing 4 µmolal CA significantly reduced the CO2 -H2 O equilibration time for deionized water and artificial seawater (ionic strength = ~0.6) from ~19 h and ~23 h to ~0.30 h and ~0.77 h, respectively at 25°C. CONCLUSIONS: This enzymatically catalyzed CO2 -H2 O equilibration method is time-efficient, cost-effective, requires no additional data correction procedure, and can be used for most commercially available CO2 -H2 O equilibration devices without any modification.