Zero-Valent Iron on Mars

Zero-Valent Iron on Mars:

An Alternative Energy Source for Methanogens

Courtesy: NASA

Brendon K. Chastain University of Arkansas Dept. of Biological Sciences Methanogens – Good Model for Possible Subsurface Life on Mars

• Can grow in temperatures below 0 C (Reid et al., 2006)

• Can tolerate exposure to extremely low pressures (Altheide and Kral, 2008)

• Phylogenetically primitive

*Mars in a laboratory! Æ Fe0 on Mars

• Several large iron meteorites composed primarily of Fe0 found on Mars’ surface. (Schroder et al., 2008)

• Stony-irons containing substantial Fe0 also found in what might be a strewn field. (Schroder et al., 2008)

Courtesy: NASA/CORNELL Micrometeorite Delivery

• Just like Earth, Mars is bombarded with meteoritic debris, much of it Fe0. – Substantially thinner atmosphere increases the amount reaching the surface

• Flynn and McKay (1990) estimate as much as 29% of Martian soil from meteorites. – Up to 59,000 tons per year delivered to the surface Shock-reduction from Impacts

• Impacts can lead to 1 shock-reduction of iron- bearing minerals resulting in nanophase Fe0. • Numerous studies confirm Fe0 in SNC meteorites. (e.g. Kurihara et al., 2009) • This has been mimicked in the laboratory using JSC Mars-1 regolith 1) TEM image of NWA 2737 olivine. Small, dark (electron-dense) spherules simulant. (Moroz et al., are consistent with α-iron kamacite [after 2009) Treiman et al., 2007] (Pieters et al., 2008) Fe0 Source Summary

• Large meteorites deliver exogenous Fe0 • Micrometeorites deliver exogenous Fe0 • Large impactors generate and spread nanophase Fe0 due to shock-reduction of iron-bearing minerals

• May lead to substantial buildup of Fe0 over time Fe0 Relationship to Methanogens

• Protons in solution can react with Fe0 to produce

H2, but the reaction is not thermodynamically favorable.

• However, a sink for H2 can drive the reaction. • Daniels et al. (1987) show that methanogens in

nutritive medium can utilize the H2.

Daniels et al. (1987) This Study:

•Fe0/any H+ in solution (energy)

• Bicarbonate buffer/CO2 (carbon/water) • Montmorillonite clay (micronutrients)

• Does methanogenic metabolism take place in these Mars-relevant conditions?

*Why montmorillonite? 14 30 M. formicicum M. barkeri Transfer #1 12 Montmorillonite Montmorillonite 25 Transfer #1

10 Transfer #2 JSC Mars-1 JSC Mars-1 20

8 JSC Mars-2 JSC Mars-2

15 Transfer #2 6 Jarosite Jarosite Methane (% vol.) Methane

Methane (%vol.) 10 4 Nontronite Nontronite

2 Buffer-only 5 Buffer-only

0 0 1 3 5 7 9 1113151719212325272931 1 3 5 7 9 1113151719212325272931 Time (weeks) Time (weeks)

90 M. wolfeii 80 Montmorillonite Montmorillonite 70 Transfer #1

JSC Mars-1 60 clay can supply 50 Transfer #2 JSC Mars-2 the micronutrient 40 Jarosite

Methane (% vol.) (% Methane 30 Nontronite requirements of 20 Buffer-only 10 methanogens. 0 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 Time (weeks) 0 Results: Fe vs. no H2

20 Feº-included Control

10 Methane Concentration (% vol.) (% Concentration Methane

0 0 102030405060708090100 Time (days) Obvious oxidation to Fe3+

*Is the darker color of the montmorillonite an indication of Fe(OH)2? 40Comparison to Previous Work

20 Initial study before transfer Initial study after transfer Feº-included

10 Methane Concentration (% vol.) Concentration (% Methane

0 020406080100 Time (days) Concluding Remarks

•Fe0 is available on Mars

•CO2 is available on Mars • Montmorillonite-like clays are available on Mars • Given the right environmental conditions, these three materials can support methanogenic metabolism • The temperature was not exactly Mars- relevant, BUT…