O	8

Oxygen

Abundance: 0.15% atmosphere 46,6% crust

Oxygen (periodic table symbol: O⁸) is a chemical element that can be found in the atmosphere and in most minerals on Mars. Almost half of the mass of the Martian crust is Oxygen, bound up in various minerals. Oxygen is created in stars from the fusion of Carbon and Helium. Oxygen has 8 protons and the most common isotope is oxygen 16. O₁₇ and O₁₈ exist and are stable. Oxygen needs two electrons to fill its outer electron shell, which makes it a powerful oxidizer. (Only Fluorine is a more powerful oxidizer, but Fluorine is a fairly rare element.)

Alga producing oxygen

Relevance for life

The metabolism of human beings, animals and various microbes depends on oxygen. The atmosphere of Mars contains only 0,15 % oxygen, which is not enough to support animal or human life. If Oxygen is common in Mars' atmosphere, an Ozone layer will build up which will protect the surface from Ultraviolet light.

Production

Oxygen can be produced in situ:

in greenhouses by plants.
in photobioreactors by algae.
by reduction of carbon dioxide from the martian atmosphere, or carbonate minerals via either molten salt reduction^[1] or via MOXIE style solid oxide electrolysis.
by reduction of oxide minerals, either at low temperature in aqueous solution^[2] or at high temperature in molten salt^[3]. This is required to free up metals from many ores.
by electrolysis of water
by the decomposition of perchlorates in the soil.
by thermal decomposition of water through the Sulfur/Iodine^[4] or Zinc/Sulfur/Iodine^[5] cycles.

Electrolysis

Submarines are a fairly good analog for a Mars habitat, a sealed system that has to manufacture oxygen and remove carbon dioxide. How Submarines produce oxygen^[6]

On a submarine they use electrolysis to create oxygen. Two electrodes, positive and negative charged. Pure water is required because, for example, salt water will create chlorine gas which will kill people. On a submarine they use reverse osmosis to filter out the salt. They take pure water and add potassium hydroxide KOH as a catalyst to make the electrolysis go easier. The hydrogen they create is exhausted from the boat.

Gas monitoring

Monitoring the atmosphere in every compartment in the habitat is required in order to ensure the proper distribution of oxygen and the to measure the concentration of contaminants that can cause health or fire risks. CO2 is usually monitored as a proxy for oxygen, as the toxic concentration of CO2 is reached much faster than the lowest threshold for respiration.

The gasses they monitor in a submarine (measured in TORR) are: O₂, CO₂, H₂, N₂, H₂O, pressure (a total of all of these). Other gasses monitored in mTORR are: CO, R114 (refrigerant), TRICH, ALIPHAT, AROMAT, BENZENE, R134A (refrigerant). These are gases used in systems that should not escape into the breathable air. For all these gasses they have calibration samples to confirm the monitors are working correctly.

For each bad gas being monitored they have hand held sniffers that detect concentrations to find a leak. Sniffers work just like a geiger counter or metal detector. The sniffer only detects relative concentration, it is not a numerical measurement. Consequently it has a small, medium, or large setting to vary sensitivity.

Emergency supplies

Emergency supplies or backup supplies in small vehicles is provided by burning a Chlorate candle (aka an Oxygen candle). Iron (Fe) and Sodium Chlorate (NaClO₃).

Fe + O₂ -> Fe₂O₂ + heat
heat + NaClO₃ -> NaCl + O₂

Oxygen candles are used on the space station.
Fires are classified in various ways. A Class Delta fire (self oxidizing fire), like an oxygen candle, cannot be extinguished, it has to burn out.