Solar wind implantation

Extraterrestrial dust particles can be proven to be nonterrestrial by a variety of methods, depending on the particle si2e. Unmelted particles have high helium. He, contents resulting from solar wind implantation. In 10-)J.m particles the concentration approaches l/(cm g) at STP and the He He ratio is close to the solar value. Unmelted particles also often contain preserved tracks of solar cosmic rays that are seen in the electron microscope as randomly oriented linear dislocations in crystals. Eor larger particles other cosmic ray irradiation products such as Mn, Al, and Be can be detected. Most IDPs can be confidently distinguished from terrestrial materials by composition. Typical particles have elemental compositions that match solar abundances for most elements. TypicaUy these have chondritic compositions, and in descending order of abundance are composed of O, Mg, Si, Ee, C, S, Al, Ca, Ni, Na, Cr, Mn, and Ti. 

Figure 7.1 Elemental abundance of noble gases relative to cosmic abundance (Anders Grevesse, 1989). Data for Earth (atmosphere), SW (solar wind implanted on A1 foils on the moon), Lunar (solar wind implanted on lunar soils), Q (chondrites), and Mars are from Table 3.2.

These data show that, because the fines derive from crystalline rocks, a carbon component has been added to the fines. The total carbon concentration in Apollo 11 fines increases with decreasing particle size, indicating that there is a surface correlationS4,67 It has been suggested54 therefore, that solar wind implantation of carbon into the surfaces of the fines makes a significant contribution to the total carbon, although a meteorite contribution cannot be discounted. 

CS2 HRMS Solar wind implanted carbon in troilite (FeS) 43,50)... 

Fig. 6. Concentrations (10ls atoms/g) of CD4 and CH4 (as carbon) released by DQ dissolution versus concentration of solar wind implanted 26Ar (1015 atoms/g) in Apollo 11, 12 and 14 fines...

The observed noble-gas abundances and isotopic ratios on Venus are summarized in Tables 3 and 4. The helium mixing ratio is a model-dependent extrapolation of the value measured in Venus upper atmosphere, where diffusive separation of gases occurs. The main differences between Venus and Earth are that Venus is apparently richer in He, Ar, and Kr than the Earth, and the low " Ar/ Ar ratio of — 1.1 on Venus, which is —270 times smaller than on Earth. The low " Ar/ Ar ratio may reflect more efficient solar-wind implantation of Ar in solid grains accreted by Venus and/or efficient early outgassing that then stopped due to the lack of plate tectonics. Wieler (2002) discusses the noble-gas data. Volkov and Frenkel (1993) and Kaula (1999) describe implications of the " Ar/ Ar ratio for outgassing of Venus. 

The atmosphere of Mars has several features that are distinct from that of the Earth and require a somewhat different planetary history. At likely nebular temperatures and pressures at its radial distance. Mars is too small to have condensed a dense early atmosphere from the nebula even in the limiting case of isothermal capture (Hunten, 1979 Pepin, 1991). Therefore, regardless of the plausibility of gravitational capture as a noble-gas source for primary atmospheres on Venus and Earth, some other way is needed to supply Mars. This may include solar-wind implantation or comets. An important feature is that, in contrast to Earth, martian xenon apparently did not evolve from a U-Xe progenitor, but rather from SW-Xe. This requires that accreting SW-Xe-rich materials that account for martian atmospheric xenon are from sources more localized in space or time and so have not dominated the terrestrial-atmospheric xenon budget. There are insufficient data to determineif the martian C/N ratio is like the terrestrial value, but it appears that the initial C/H2O ratio may have been. Further constraints on the sources of the major volatUes are required. 

Nitrogen concentrations are much larger in lunar soils than in lunar rocks (Mathew and Marti 2001) and in stepwise analyses most of the nitrogen in soils is released in the same fractions as solar wind implanted noble gases (e.g., Frick et al. 1988). This indicates that most of the nitrogen in lunar soils is a trapped component. 

Johnson JR, Swindle TD, Lncey PG (1999) Estimated solar wind-implanted helium-3 distribution on the Moon. Geophys Res Lett 26 385-388... 

Fig. 1. Carbon abundances as a function of values for a suite of 16 Apollo 16 soils, compared with predictions of a model based primarily on solar-wind implantation and proton stripping. The curves represent predictions for three trial values of the model parameter which is a rate constant incorporating both production and diffusive loss of methane. The numbered data points are for samples known from other evidence to be anomalous. The remaining data appear to be loosely consistent with the model predictions. From Kerridge et al (1974).

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