# Presentation: 144034

**Biological potential of martian hydrothermal systems**

**Introduction**

-  We have developed numerical geochemical models of martian hydrothermal systems using the EQ3/6 computer program.
-  The aim of this study is to determine whether the energy yield of chemical reactions in the modeled systems are sufficient to support potential life.
-  We have calculated the energy yield of several reactions that are used by terrestrial microorganisms for metabolism.

## Calculating Energy Yield

- <date/time>

**Calculating Energy Yield**

## Model Overview

-  Define host rock and groundwater composition
-  React rock and groundwater at high temperature to produce hydrothermal vent fluid
-  React hot vent fluid with increments of the original cool groundwater to simulate mixing
-  Calculate the energy yield of the three metabolic reactions as a function of temperature (mixing ratio)

- The modeled systems simulate the convective circulation of surface or near-surface derived waters to a depth of ~ 2km in the martian crust, where they may react with rock in the vicinity of  a hot magmatic intrusion, and subsequently mix with fresh inflowing groundwater.

## Groundwater Compositions

- To explore the dependence of energy yield on water composition, we have defined three different groundwaters.
- Water 1 - Pure H2O + present martian atmosphere
- Water 2 - Water 1 in equilibrium with a Pathfinder composition soil
- Water 3 - Water 1 in equilibrium with a less oxidized Pathfinder
-                  composition soil

## LEW 88516  Host Rock

- LEW 88516 is an ultramafic rock whose composition is similar to the martian mantle.

## Chassigny  Host Rock

- Chassigny is a dunite  - an ultramafic rock composed primarily of olivine.

## Shergotty Host Rock

- Shergotty is a basalt, which may have formed in a lava flow at the surface of Mars.

## Model 1 LEW-Water 1 vent fluid + Water 1 groundwater

*Precipitation Allowed*

*Precipitation Suppressed*

## Model 2 LEW-Water 2 vent fluid + Water 2 groundwater

*Precipitation Allowed*

*Precipitation Suppressed*

## Model 3 LEW-Water 3 vent fluid + Water 3 groundwater

*Precipitation Allowed*

*Precipitation Suppressed*

## Model 4 Chassigny-Water 1 vent fluid + Water 1 groundwater

*Precipitation Allowed*

*Precipitation Suppressed*

## Model 5 

- Chassigny-Water 2 vent fluid + Water 2 groundwater

*Precipitation Allowed*

*Precipitation Suppressed*

## Model 5 cont.

- Chassigny-Water 2 vent fluid + Water 2 groundwater

*Precipitation Allowed*

*Precipitation Suppressed*

## Model 6 

- Chassigny-Water 3 vent fluid + Water 3 groundwater

*Precipitation Allowed*

*Precipitation Suppressed*

## Model 7 

- Shergotty-Water 1 vent fluid + Water 1 groundwater

*Precipitation Allowed*

*Precipitation Suppressed*

## Model 8 

- Shergotty-Water 2 vent fluid + Water 2 groundwater

*Precipitation Allowed*

*Precipitation Suppressed*

## Model 9 

- Shergotty-Water 3 vent fluid + Water 3 groundwater

*Precipitation Allowed*

*Precipitation Suppressed*

## Model 9 cont. 

- Shergotty-Water 3 vent fluid + Water 3 groundwater

*Precipitation Allowed*

*Precipitation Suppressed*

## Estimated Productivity

- The biomass, or biological productivity, which may be derived from the energy yield of a given reaction depends on the amount of energy necessary for cellular synthesis.  We assume that the typical anaerobic microbe requires ~9700 cal/g cells (see for instance Heijnen & van Dijken, 1991).
- The maximum energy yield was found from sulfate reduction in Model 6.  As much as 0.5 g microbes could be generated for each kg of hydrothermal fluid.  Hydrothermal vent fluxes for typical terrestrial systems are ~5105 kg/h, which would result in the generation of 250 kg bugs/hr!  This is clearly a tremendous yield.  The more modest energy yield of sulfate reduction in Model 9 results in as much as 0.002 g microbes/kg hydrothermal fluid, which for a typical terrestrial vent flux would generate 1 kg bugs/hr.

## Conclusions

- Significant energy yield is obtained from a variety of mixing models; it is therefore likely that at least some environments on Mars are similar to the modeled environments, and suitable for life from the standpoint of energy.
- In most cases, mineral precipitation to equilibrium results in negligible energy yields, although there are a few notable exceptions.  Models in which energy yields are not strongly dependent on mineral precipitation may be better candidates for suitable  abodes of life.  Models using the Water 3 groundwater composition tend not to have a strong dependence on precipitation.
- The highest energy yields result from models in which both the host rock composition and the groundwater composition are reduced.  This is a somewhat unexpected result, and arises because hydrogen is the limiting reactant for the majority of the modeled reactions.  However, Mars is a largely basaltic planet, and although huge energy yields might be possible from a highly ultramafic host rock, it is unlikely that many analogous systems exist.