NEEP602 Course Notes (Spring 1996)
Resources from Space

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Concentrations of Various Volatiles in Apollo 11 Regolith

Concentrations of important volatile elements in Apollo 11 regolith as indicated by analyses of various samples of regolith fines are given in Table 1. Hydrogen, helium, carbon, and nitrogen are derived mainly or entirely from the solar wind. Sulfur is derived at least mainly from sulfides in regolith particles. It is now established that concentrations of solar wind gases in regoliths are a function of maturity, which in turn is a function of length of exposure to the solar wind. It is also established that the helium content of regolith is a function of the ilmenite content, hence in general to the TiO content. Bustin and Gibson (1992) conclude that the hydrogen content is also related to the TiO content, but this is not clear from the data presented in their Table 1. Sample 75261, mature regolith from Apollo 17 containing 9-10% TiO, is reported to contain 60.2 wppm H. However, sample 15261, with only 1.50% TiO, is reported to contain 58.2 wppm H. The data of their table suggest that H content of regolith is far more a function of maturity than of TiO content.

Release of various gases from Apollo 11 fines on heating has been studied by Gibson and Johnson (1971). Solar wind helium is almost entirely released between 300o and 700oC, along with most of the hydrogen. The ratio of H to He in regolith (7-7.5) is lower than the ratio in the solar wind (17), possibly due to diffusion of H from the samples.

At temperatures below 500oC, CO is the major C-containing gaseous phase. Its source is uncertain. CO is further released at 675oC and 1125oC, and again above 1200oC. At temperatures above 700oC the principal gaseous phase released is mass 28, CO and/or N. The CO is believed derived by reaction of C-containing phases, such as cohenite [(Fe, Ni)3C], with silicates.

Sulfur is released as HS and SO. Evolution of the two gases begins above 900oC, which means that they will not be present during heating of the soil for release of hydrogen and helium. Most of the sulfur is evolved above 1,000oC.

As indicated in my previous report, various studies have shown that the solar wind gases are heavily concentrated in the finer size fractions of the regolith, since implantation of the gases is a surface phenomenon and is therefore proportional to particle surface area per unit of mass. This must be taken into account in devising and testing methods of processing the regolith on the Moon.

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Eugene N. Cameron

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