Perchlorate is a chlorine-oxygen salt and a strong oxidant. The Wet Chemistry Laboratory on Phoenix wetted soil from the polygon-patterned northern plains and measured 0.4 percent to 0.6 percent perchlorate by mass in the leachate of each sample. Surface samples and samples from the edge of the ice table, about 5 cm down, were not meaningfully different. [1]
That range is the number this sheet stores. It is not a planet-wide average. Dust may move salts around, and papers argue about that. This page does not promote the Phoenix range into a global constant.
Why a designer hits it
Water melted out of soil is not a tank of drinking water. Perchlorate rides with the salts. On Earth it interferes with the thyroid's use of iodide. This sheet does not set a dose, a drinking limit, or a medical clearance. Crew budget is the mass of potable water in the life-support baseline. It is not a treatment plant.
The same oxidant bothers a search for organic molecules. Heat can turn chlorine in the soil into compounds that mask or destroy the signal. Life on Mars keeps that caution. A greenhouse at Mars ambient pressure and a greenhouse inside a cabin are different machines. This page does not size either one.
What processing means here
The literature talks about separating ice or brine from the soil, washing the salt or breaking it with heat, and then testing whatever oxidant is left. This sheet names those steps and stops. It does not pick a temperature, a solvent volume, or a residual limit. If a later page wants a worked water mass, the perchlorate test has to be one of the inputs, not a footnote.
Subsurface ice is the evidence that ice is there. Site dossiers does not award a place for having less of this salt, because we have not stored a perchlorate map.
See also
What links here
References
- Hecht et al. Detection of perchlorate and the soluble chemistry of martian soil at the Phoenix lander site. Science 325 (2009). 0.4 to 0.6 percent by mass. https://doi.org/10.1126/science.1172466