Earth, planetary features

Figure 3. The noble gas abundance patterns of the Earth and Cl chondrites (see Wider 2002, this volume), normalized to Si and the solar composition. The Earth shows greater depletion the light noble gases, similarly to Cl chondrites. However, the terrestrial Xe/Kr ratio is lower than chondrites. The difference between the terrestrial pattern and the dotted line, which parallels the Cl Chondrite pattern, was once interpeted to reflect missing Xe sequestered some where on Earth, although the lower terrestrial Xe/Kr ratio now appears to be a planetary feature.

The search for signs of life, present or past, is an important goal of NASA s robotic solar system exploration programs and, ultimately, for its astronomical programs designed to probe the gross characteristics of extrasolar planetary systems. To date, that search has been governed by a model of life that is based on the life that we know on Earth—terran life. Several features of terran life have attracted particular focus ... 

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. 

Such calculations also show that, fortunately for us, the Earth will probably stay at roughly the same distance from the sun for the next 100 million years, although this cannot be established with certainty As one worker in this field observed, [c]haos appears to be a common feature of planetary systems... [so] it s not surprising that our real solar system is chaotic. It would be surprising if it weren t. ... 

Space exploration by planetary missions from Earth has revolutionized our view of these moons and planets. Europa, Jupiter s second large moon, is easily among the most fascinating bodies. Its surface features suggest that it is a tectonically active body that is... 

Tsunogai, U., Ishibashi, J., Wakita, H., Gamo, T., Watanabe, K., Kajimura, T., Kanayama, S., and Sakai, H., 1994. Peculiar features of Suiyo Seamount hydrothermal fluids, Izu-Bonin arc Differences from subaerial volcanism. Earth and Planetary Science Letters, 126 289-301. 

The lower terrestrial Xe/Kr ratio has since usually been considered a feature of the Earth (see, however, Ozima and Podosek 1999 and Rayleigh distillation section below). Although relative abundances in chondrites were historically called the planetary pattern based on similarities with the Earth s atmosphere, and this in turn drove the search for the missing Xe , it is now clear that these trapped meteoritic gases do not have such direct relevance to the planets, and so are no longer properly termed planetary . However, the reason why the Earth does not exhibit a systematic depletion pattern relative to solar gases (Fig. 2) still requires explanation. 

Spencer D (1972) GEOSECS IE The 1970 North Atlantic Station Hydrographic features, oxygen, and nutrients. Earth and Planetary Science Letters 16 91-102. 

The planetary Rossby waves responsible for the distortion of the zonal jets in winter, and for the sudden warming phenomenon, are quasistationary that is, these waves move only slightly with respect to the Earth s surface. The marked differences between the wintertime circulation of the Northern and Southern hemispheres is due to the weaker amplitude of quasistationary planetary waves in the latter, as illustrated in Fig. 9. This, in turn, is probably related to the concentration of continental land masses in the Northern Hemisphere. Major orographic features are known to excite planetary waves when the tropospheric jet streams blow strongly across them, as is the case during winter the thermal contrast between continents and oceans is also known to excite planetary waves. 

Planetology and astrogeology are separate branches of science that examine the physical and chemical characteristics of the planets and minor bodies in the solar system. The principle difference between these two scientific disciplines is that planetology is inclusive of all planetary bodies, while astrogeology concentrates on those worlds that are basically similar to the Earth. Scientists within the field of planetology can study a variety of topics that include planetary atmospheres, interiors, orbital characteristics, the potential for life, and all aspects of planetary formation and evolution. In comparison, astrogeology essentially concentrates on the various surface features and geological processes of the Earth as seen on other worlds. 

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