Planetary surface

Another family of feedbacks arises because the radical differences in the albedo (reflectivity) of ice, snow, and clouds compared to the rest of the planetary surface, which causes a loss of the absorption of solar radiation and thereby cools the planet. Indeed, the high albedo of snow and ice cover may be a factor that hastens the transition into ice ages once they have been initiated. Of course, the opposite holds due to decreasing albedo at the end of an ice age. As simple as this concept may appear to be, the cloud-albedo feedback is not easy to quantify because clouds reflect solar radiation (albedo effect) but absorb... 

For measurements on planetary surfaces, the instrument has to meet special requirements. In the case of Mars, MIMOS II is able to work at temperatures as low as — 140°C and an average atmospheric pressure of 7 mbar of CO2 [36,40,47, 52-55]. 

With the exception of these fractionation pathways, studies of igneous systems chiefly focus on the potential of Li isotopes as geochemical tracers fingerprinting the cycling of Li derived from specific (low-temperature) sources through the solid Earth. The sections below deal with observations of Li isotopes in high-temperature systems, and the mechanisms for low-temperature fractionation processes are discussed after, imder the heading, Planetary surface systems. ... 

PLANETARY SURFACE SYSTEMS Mass fractionation in hydrologic cycle of Li... 

Beryllium-10, like 14C, 26Al, and 36C1, is used to infer the cosmic-ray exposure history of a meteorite or a planetary surface. 

The fraction of incoming cosmic rays that generate nuclear reactions is quite low. In a meteorite traveling in space, about one in 108 of the target atoms undergoes a nuclear reaction in a 10-Myr period. However, the cosmogenic nuclides that they produce can be measured to estimate the time that an object has been exposed to cosmic rays. Table 9.1 shows some of the nuclides that are used to estimate cosmic-ray exposure ages in meteorites and in materials from planetary surfaces. 

Sharma, S.K. Lucey, P.G. Ghosh, M. Hubble, H.W. 8c Horton, K.A. Stand-Off Raman Spectroscopic Detection of Minerals on Planetary Surfaces Spectroc. Acta Pt. A-Molec. Biomolec. Spectr. 2003, 59, 2391-2407. 

Between all the factors governing a re-distribution of carbon above (and below) the planetary surface, two processes of mainly regional character play the most... 

This paper reviews briefly the mechanisms responsible for mineral luminescence, then turns to less common modes of excitation, particularly ion and radical recombination luminescence, and finally discusses luminescence on the scale of remote sensing of planetary surfaces. 

In orthopyroxenes, the very intense Fe2+/M2 site bands near 11,000 cm-1 and 5,000 cm-1 in spectra measured at atmospheric pressure (cf. fig. 5.15), as well as the Fe2+/Ml site band located at 8,333 cm-1, show pressure-induced blue-shifts (Shankland et al., 1974 Mao and Bell, 1971). At elevated temperatures, the Fe2+/M2 site 1 micron (11,000 cm-1) band shows negligible thermal shifts (Sung et al., 1977 Singer and Roush, 1985). However, the 2 micron (5,000 cm-1) band shows a significant red-shift in orthopyroxenes and a blue-shift in clinopyroxenes (Singer and Roush, 1985). These effects, which have important applications in remote-sensed spectral measurements of hot planetary surfaces, are described in chapter 10 ( 10.7). 

Remote-sensing compositions of planetary surfaces applications of reflectance spectra... 

In remote-sensed reflectance spectra of planetary surfaces measured through Earth-based telescopes, the Sun is the illuminating source. Light reaching... 

Figure 10.5. The 1 pm versus 2 pm pyroxene spectral determinative curve widely used to identify compositions and structure-types of pyroxenes on planetary surfaces (from Adams, 1974). Circles refer to room-temperature data. Numbered squares (orthopyroxene En86Fs14) and triangles (clinopyroxene Wo42En51Fs7) represent spectral data obtained at the temperatures (1) 80 K (2) 173 K (3) 273 K (4) 373 K and (5) 448 K (modified from Singer Roush, 1985).

The contrasting temperature-induced shifts of the pyroxene 1 and 2 pm bands could lead to erroneous estimates of the composition and, to a lesser extent, structure-type of a pyroxene-bearing mineral assemblage deduced from the remote-sensed reflectance spectrum of a hot or cold planetary surface if room-temperature determinative curves, such as that shown in fig. 10.5, are used uncritically. For example, remote-sensed spectra of planets with hot surfaces, such as Mercury and the Moon, would lead to overestimates of Fe2+ contents of the orthopyroxenes and underestimated Fe2+ contents of the clinopyroxenes (Singer and Roush, 1985). Planets with cold surfaces, such as Mars and the asteroids, could produce opposite results. On the other hand, the room-temperature data underlying the pyroxene determinative curve shown in fig. 10.5 may impose constraints on the compositions of pyroxenes deduced from telescopic spectra of a planet with very high surface temperatures, such as Mercury. 

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