Mars polar caps

Kargel, J.S. Tanaka, K.L. Baker, G. Komatsu, G. MacAyeal, D.R. Formation and dissociation of clathrate hydrates on mars polar caps, northern plains and highlands. Lunar Planet. Sci. 2002, XXXI. www.lpi.usra.edu/meetings/lpsc2000/pdf/ 1981.pdf... 

FIGURE 6.24 The polar ice caps on Mars extend and recede with the seasons. They are mostly solid carbon dioxide and form by direct conversion of the gas into a solid. They disappear by sublimation. Although some water ice is also present in the polar caps, the temperature on Mars never becomes high enough to melt it. On Mars, ice is just another rock. 

More than any other planet. Mars has captured our attention and fueled our speculations. Much of this interest relates to the possibility of martian hfe, as championed by Percival Lowell in the last century and subsequently in scientihc papers and science fiction. Lowell s argument for life on Mars was based partly on geochemistry, in that his assessment of the planet s hospitable climate was dependent on the identification of H2O ice rather than frozen CO2 in the polar caps. Although this reasoning was refuted by Alfred Wallace in 1907, widespread belief in extant... 

Polar caps—The deposits of frozen carbon dioxide at Mars s poles. The ice caps advance and recede with the changing Martian seasons, and bear a strong resemblance to Earth s polar regions. 

Icy satellites have an icy crust and mantle and are composed of mixtures of ice and silicates. Stripe patterns showing layered structures with different sand contents have been discovered on the polar cap on Mars. There could be a wide range of temperature conditions from the melting point of ice to below 100 K in icy satellites and on Mars. Therefore, it is important to study the rheological properties of ice-silicate mixtures at wide temperatures to elucidate the tectonics of icy satellites and the flow dynamics of ice sheets on Mars. 

Oamma-ray spectrometers have been successfully used in the exploration of the lunar and Martian surfaces, and a gamma-ray spectrometer was a significant component of the Mars Surveyor mission. Its goals were to quantitatively determine elemental abundances on the Martian surface, to map the distribution of water, to study the seasonal polar caps, and to investigate the nature of cosmic gamma-ray bursts. 

Scientific interest in Mars goes back to the seventeenth century and the work of Galileo Galilei, Johannes Kepler, and Giovanni Domenico Gassini— the last of whom, in 1666, observed the Martian polar caps and calculated the length of the Martian day. The apparent Earth-like nature of Mars led French author Bernard le Bouvier de Fontenelle in 1688 and British astronomer William Herschel in 1784 to speculate on the nature of life on Mars. 

Fig. 124.1 Schematic of the runaway greenhouse scenario. (1) Various planetary engmeering techniques are used to warm volatile-rich regions on Mars (2) carbon dioxide in the polar caps tmd the regoUth starts to vaporize (3) the thicker atmosphere warms the surface and hence causes a further release of gases. If positive feedback is strong enough, self-sustaining outgassing may occur as a result of a comparatively trivial forcing...

The planet Pluto as well as many satellites in the outer Solar System, such as Charon, Triton, and others belong to the group of relatively small objects with significant amounts of ices on the surface (see also Schmitt et al, 1998). The atmospheric surface pressure is then controlled by the surface temperature, the vapor pressure of the frozen volatiles, and the escape rate of the gases. Even Mars, with its CO2 polar caps, may be included in this group. Pluto and Charon are discussed together with comets and asteroids in Chapter 7. 

Herr, K. C. Pimentel, G. C. (1969). Infrared absorptions near three microns recorded over the polar cap of Mars. Science, 166,496-9. 

Hess, S. L., Henry, R. M., Tillman, J. E. (1979). The seasonal variation of atmospheric pressure on Mars as affected by the south polar cap. Journal of Geophysical Research, 84,2923-7. 

Fig. 3.5 Mars seen from the Earth orbiting Hubble Space Telescope, HST. One of the polar caps is clearly seen as well as some surface features and clouds in its atmosphere. Image Credit HST...

Mariner 9 images showed equatorial sinuous channels on Mars. Sagan, Toon and Gierasch, 1973 [288] mentioned two possible stable climates one that resembles the present day climate on Mars, the other which has atmospheric pressure of about 1 bar. The triggers for a transition from one state to another are changes in the obliquity, solar luminosity and albedo variations of the polar caps. 

Voyager s radio occultations, the infrared spectrometer and the ultraviolet spectrometer experiments, all gave us information about the atmosphere. These data are all consistent with a nitrogen atmosphere in what is called vapor pressure equilibrium. In vapor pressure equilibrium, the gas in the atmosphere comes from the sublimation of ice for the same material frozen on the surface. The amount of gas in the atmosphere is controlled by the temperature of the ice, and the atmosphere acts to keep the ice at a constant temperature by the transport and condensation of the gas from warm to colds areas. Mars primarily carbon dioxide atmosphere is in a similar equilibrium with its polar carbon dioxide caps. 

Mars has numerous earthlike features. There are large, extinct volcanoes dotting its surface, eroded channels where water once flowed freely, and ice caps covering its poles that look very much like Earth s polar regions. But, the thin Martian atmosphere is made mainly of carbon dioxide. Although Mars may now be a cold, dead world, the variety of features on its surface suggests a complex and fascinating past. 

There are three planets other than Earth in the inner solar system. The innermost is Mercury tiny, barren, and hard to observe as it is located near the Sun. Next comes Venus, the planet nearest in size and mass to Earth, but swathed in clouds a bland, featureless ball through the small telescope. Mars, half again as far from the Sun as Earth, is different. Features are distinguishable on its surface, and it sometimes shows polar ice caps that look much like Earth s. 

Atmospheric carbon dioxide is the source of Mars s polar ice caps. Atmospheres act like giant insulators for planets, preventing heat from radiating away to space. Mars s thin atmosphere holds very little heat—a blazing summer day on Mars might get up to the freezing point of water 32 E (0 C), but at night the temperature plummets well back below 0 E (18 C). At the poles, temperatures drop well below -lOO E (-73 C), sufficiently cold for the carbon dioxide in the atmosphere to freeze. Mars s polar ice caps consist of frozen carbon dioxide with an underlayer of ice. 

Earth follows a nearly circular path around the sun completing a cycle in one year. The 23.5° tilt of Earth s axis is responsible for the four seasons. Mars has an axis tilted to a very similar degree to that of Earth. The seasonal contrasts on Mars are enhanced because its orbit departs from circular and it is closer to the Sun during part of the Martian year. Lowell observed significant seasonal color changes on Mars and shrinking and expansion of its polar ice caps. He imagined construction of the above-mentioned canali by an advanced civilization. H. G. Wells published his novel The War of the Worlds in 1898 and Lowell published a book titled Mars as the Abode of Life in 1908. 

Mars -- the surface of Mars contains numerous craters, active and extinct volcanoes, ridges and valleys with extremely deep fractures. Iron oxide found in the dusty soil makes the surface seem rust colored and the skies seem pink in color. The atmosphere is composed of carbon dioxide, nitrogen, argon, oxygen and water vapor. Mars has polar regions with ice caps composed of water. Mars has two satellites. Mars was named after the Roman war god. 

In a dry atmosphere, as occurs over the polar Ice caps, on Mars H2 is the main source of odd hydrogen through photodlssoclatlon of H2, and the reaction... 

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