Atmosphere of Mars

Without carbon, the basis for life would be impossible. While it has been thought that silicon might take the place of carbon in forming a host of similar compounds, it is now not possible to form stable compounds with very long chains of silicon atoms. The atmosphere of Mars contains 96.2% CO2. Some of the most important compounds of carbon are carbon dioxide (CO2), carbon monoxide (CO), carbon disulfide (CS2), chloroform (CHCb), carbon tetrachloride (CCk), methane (CHr), ethylene (C2H4), acetylene (C2H2), benzene (CeHe), acetic acid (CHsCOOH), and their derivatives. 

A gaseous element, oxygen forms 21 % of the atmosphere by volume and is obtained by liquefaction and fractional distillation. The atmosphere of Mars contains about 0.15% oxygen. The element and its compounds make up 49.2%, by weight, of the earth s crust. About two thirds of the human body and nine tenths of water is oxygen. 

The gas is prepared by fractionation of liquid air because the atmosphere contains 0.94% argon. The atmosphere of Mars contains 1.6% of 40Ar and 5 p.p.m. of 36Ar. 

Krypton is present in the air to the extent of about 1 ppm. The atmosphere of Mars has been found to contain 0.3 ppm of krypton. Solid krypton is a white crystalline substance with a face-centered cubic structure which is common to all the "rare gases."... 

The atmosphere of Venus is chiefly carbon dioxide in a concentration much higher than that found on Earth. Surprisingly, no evidence has been found for carbon monoxide, though ultraviolet light decomposes CO2 to form CO. The atmosphere of Mars is thought to be largely nitrogen (around °8%) and some carbon dioxide. 

The photo below, taken by the Ttl/ng spacecraft, shows that the surface of Mars has been eroded, apparently by liquid water. More recent photos transmitted by Spirit and Opportunity convince scientists that this was the case. Apparently, Mars was once much warmer than it is today. Planetary scientists speculate that at one time the atmosphere of Mars may have contained large amounts of carbon dioxide, setting up a greenhouse effect that made the surface of that planet warmer and wetter. Might there, then, have been life on Mars at some earlier time Molecular stmctures found in meteorites thought to come from Mars have been interpreted to show that there was once life there, but these results are controversial. 

Occurrence. Carbon is distributed very widely in nature as calcium carbonate (limestone). Coal, petroleum and natural gas are chiefly hydrocarbons. Carbon is found as carbon dioxide in the atmosphere of the earth and dissolved in all natural waters. The atmosphere of Mars contains 96% C02. It is plentiful in the sun, stars, comets and the atmospheres of most planets. 

Mass-independent isotopic fractionations are widespread in the earth s atmosphere and have been observed in O3, CO2, N2O, and CO, which are all linked to reactions involving stratospheric ozone (Thiemens 1999). For oxygen, this is a characteristic marker in the atmosphere (see Sect. 3.9). These processes probably also play a role in the atmosphere of Mars and in the pre-solar nebula (Thiemens 1999). Oxygen isotope measurements in meteorites demonstrate that the effect is of significant importance in the formation of the solar system (Clayton et al. 1973a) (Sect. 3.1). 

The three peaks observed at 1474, 1332, and 1119 A arc assigned by Winter et al. (1052) to the A , Tl and Z states, respectively, onatheoreti-cal basis. Recently the measurement has been extended beyond 1700 A [Ogawa (755), Hcimcrl (461), Shcmansky (871)] as the importance of the photochemistry of C02 in the lower atmosphere of Mars and Venus has been recognized. 

It is known that the main constituent of the atmospheres of Mars and Venus is C02. The results of the photochemical studies of C02 in the laboratory indicate that C02 should be converted into CO and 02 with solar radiation below 2275 A. The atmospheres of Mars and Venus should thus contain substantial amounts of CO and 02. Yet it has been observed that the mixing ratio of CO and 02 relative to C02 is only on the order of 10 3 on Mars (677) and 10"3 to 10 fi on Venus (678). This unusual stability of C02 toward photolysis has been a mystery. McElroy and Donahue (677) and Parkinson and Hunten (798) have proposed an OH -H02 cycle to catalytically recombine CO + O to form C02... 

Tables VIII—2 through VIII—4 show the major and minor constituents detected in the atmospheres of Mars, Venus, and Jupiter.

Figure 10.11 Representative bright-region and daik-region reflectance spectra of Mars obtained through Earth-based telescopes and scaled to unity at 1.02 Xm (from Singer, 1985). The band near 0.87 pm in bright-region spectra is assigned to Fe3+ (6A, — T]). Pyroxenes and, perhaps, olivine, contribute to the broad band at 0.9 to 1.1 im in daik-region spectra. The 2 pm pyroxene Fe2+/M2-site band is obscured by C02 in the atmosphere of Mars. C02 is also responsible for the peaks near 1.4 and 1.62 pm.

Other books of interest include Lewis and Prinn (1984), which emphasizes the use of observational data for understanding the origin, evolution, and present-day chemistry of planetary atmospheres. Krasnopolsky (1986) focuses on chemistry of the atmospheres of Mars and Venus. He also reviews the atmospheric composition, thermal structure, and cloud measurements by the Soviet Venera and Vega missions. Chamberlain and Hunten (1987) is the classic... 

Krasnopolsky V. A. (1986) Photochemistry of the Atmospheres of Mars and Venus. Springer, Berlin. 

Melosh H. J. and Vickery A. M. (1989) Impact erosion of the primordial atmosphere of Mars. Nature 338, 487-489. 

The atmosphere of Mars has a high value of = (-1-620 160)%c (Nier and McElroy, 1977) that may be due to fractionating losses (see section 7 in Chapter 4.12), and (4.7 1.2) X 10 g N, which is equivalent to 0.7 ppb when divided into the mass of the entire planet (Owen et al, 1977). Therefore, Mars appears to have 10 " times the nitrogen on the Earth. Mathew et al (1998) reported evidence for a component in a martian meteorite with < —22%c, suggesting that, like the Earth, the solid planet may contain nitrogen that is isotopically lighter than the atmosphere, and consistent with the modification of atmospheric nitrogen isotopes by losses. 

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. 

The Earth s atmosphere contains about 0.1 part per million of xenon. Studies indicate that the atmosphere of Mars may contain about the same amount of xenon, perhaps 0.08 parts per million. The element is not known to occur in Earth s crust. 

Using the wrong units to solve a problem can be a costly error. In 1999, the Mars Climate Orbiter crashed into the atmosphere of Mars instead of flying closely by as planned. The probe was destroyed before it could collect any data. Two teams of engineers working on the probe had used different sets of units—English and metric—and no one had caught the error in time. 

Much of the current interest in the photochemistry of gaseous CO2 is due to its presence as the principal constituent of the atmospheres of Mars and Venus. While laboratory studies continue to confirm its efficient photodecomposition and inefficient recombination, neither ground-based or planetary-mission spectroscopy reveal appreciable concentrations of either CO or O2. Thus it is toward a resolution of these apparently incompatible results that much recent work has been directed. 

The problem of the stability of the CO2 atmospheres of Mars and Venus has been considered by several authors. Early mechanisms proposed to account for low abundance of CO and O2 in these atmospheres have been discarded or modified as laboratory... 

The atmospheric pressure at the surface of Mars is 5.92 X 10 atm. The Martian atmosphere is 95.3% CO2 and 2.7% N2 hy volume, with small amounts of other gases also present. Compute the mole fraction and partial pressure of N2 in the atmosphere of Mars. 

Cess, R.D., and V. Ramanathan, Radiative transfer in the atmosphere of Mars and that of Venus above the cloud deck. J Quant Spectrosc Radiat Transfer 12, 933, 1972. 

Krypton (from the Greek word kryptos, meaning hidden ), is the second heaviest of the nohle gases. It was discovered in 1898 by Sir William Ramsay and Morris Travers dining their experiments with bquid air, air that has been bquefied by coobng. It has a concentration of 1.14 ppm by volume in Earth s atmosphere. It is present in the Sun and in the atmosphere of Mars. 

Xenon (its name derived from the Greek word xenos, meaning strange ), is the heaviest of the noble gases. Discovered in 1898 in London by Sir William Ramsay and Morris Travers while engaged in their investigations of liquid air, xenon accounts for less than 1 ppm of the volume of Earth s atmosphere. It is present in the Snn and in the atmospheres of Mars, Venus, and Mercury. 

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