Carbon dioxide Mars atmosphere

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. 

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. 

Water vapour makes a sizeable contribution, and probably the largest, to radiation trapping and as the temperature increases the water vapour concentration increases. Temperature rises as a result of increased water vapour concentration and hence a mechanism for a positive feedback in the greenhouse effect that might lead to a runaway greenhouse effect. When the vapour pressure for water reaches saturation, condensation occurs and water rains out of the atmosphere this is what happens on Earth and Mars. On Venus, however, the water vapour pressure never saturates and no precipitation occurs and the global warming continues to increase. Thus Venus suffers from extreme temperatures produced by both its proximity to the Sun and the presence of water vapour and carbon dioxide in its atmosphere. 

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. 

Owens NJP (1987) Natural variations in N in the marine environment, Adv Mar Biol 24 390 51 Pagani M, Arthur MA, Freeman KH (1999a) Miocene evolution of atmospheric carbon dioxide, Paleoceanography 14 273-292... 

This co-evolution of life, atmospheric carbon dioxide and oxygen levels, and a relatively moderate climate (compared with other planets) make Earth unique. Earth has far less atmospheric carbon dioxide than Mars and Venus, neighboring planets that were formed at about the same time. The atmospheres of both Mars and Venus are made of more than 95% carbon dioxide. On these planets, there are no photosynthesizing life forms to alter the levels of atmospheric carbon dioxide or to produce oxygen. 

Catalysis may be of interest even on Mars. The Martian atmosphere consists of 95% carbon dioxide and Breedlove et al. (2001) have presented that nickel cluster catalysts could be used in a photoelectrochemical process to split carbon dioxide, according to the reaction... 

The recent advances in modem technology continue to open new opportunities for the observation of chemical reactions on shorter and shorter time scales, at higher and higher quantum numbers, in larger and larger molecules, as well as in complex media, in particular, of biological relevance. As an example of open questions, the most rapid reactions of atmospheric molecules like carbon dioxide, ozone, and water, which occur on a time scale of just a few femtoseconds, still remain to be explored. Another example is the photochemistry of the atmospheres of nearby planets like Mars and Venus or of the giant planets and their satellites, which can help us to understand better the climatic evolution of our own planet. 

The atmospheric composition of Venus is similar to that of Mars (see Table VIII—3). Carbon dioxide is the main constituent. The CO mixing ratio is about 5 x 10"5, but the Oz mixing ratio is less than 10 6. Minor constituents that are present in the Venus atmosphere but not in the Martian atmosphere are HC1 and HF in mixing ratios of 6 x 10 7 and 1.5 x 10 9, respectively. 

The photochemical processes of triatomic molecules have been extensively studied in recent years, particularly those of water, carbon dioxide, nitrous oxide, nitrogen dioxide, ozone, and sulfur dioxide, as they are important minor constituents of the earth s atmosphere. (Probably more than 200 papers on ozone photolysis alone have been published in the last decade.) Carbon dioxide is the major component of the Mars and Venus atmospheres. The primary photofragments produced and their subsequent reactions are well understood for the above-mentioned six triatomic molecules as the photodissociation involves only two bonds to be ruptured and two fragments formed in various electronic states. The photochemical processes of these six molecules are discussed in detail in the following sections. They illustrate how the knowledge of primary products and their subsequent reactions have aided in interpreting the results obtained by the traditional end product analysis and quantum yield measurements. 

Oxygen is the most abundant element in the Earth s crust and accounts for 23 % of the mass of the atmosphere. In fact, Earth is the only planet in the solar system with an oxidizing atmosphere. On Mars, oxygen provides only 0.15% of the atmospheric mass and in the atmospheres of the outer planets, oxygen is essentially nonexistent. In the hot atmosphere of Venus, the oxygen has reacted and is present mainly as carbon dioxide. In that form, and as certain other gaseous oxides, it contributes to the warming of the planet (Box 15.1). 

The necessary starting point for any study of the chemistry of a planetary atmosphere is the dissociation of molecules, which results from the absorption of solar ultraviolet radiation. This atmospheric chemistry must take into account not only the general characteristics of the atmosphere (constitution), but also its particular chemical constituents (composition). The absorption of solar radiation can be attributed to carbon dioxide (C02) for Mars and Venus, to molecular oxygen (02) for the Earth, and to methane (CH4) and ammonia (NH3) for Jupiter and the outer planets. 

Jupiter and Uranus are outer planets composed mainly of gases. Jupiter s atmosphere contains reddish-brown clouds of ammonia. Uranus has an atmosphere made up mainly of hydrogen and helium with clouds of water vapor. This combination looks greenish to an outside observer. In addition, Mars has an atmosphere that is 95% carbon dioxide, and Venus has a permanent cloud cover of sulfur dioxide that appears pale yellow to an observer. Mercury has no permanent atmosphere. Saturn has 1 km thick dust and ice rings that orbit the planet. The eight planets in our solar system are diverse, each having different chemical compositions within and surrounding the planets. Out Earth is by far the friendliest planet for human existence. 

The surface of the Sun today has an effective temperature of 5,780 K, but five billion years ago, it was cooler, about 5,500 K. The Sun was also smaller and produced 70 percent of its present radiation. Today, a 30 percent decrease in solar luminosity would destroy our ecosystems. Water would freeze, and the planet would become more like Mars. However, perhaps early Earth could have supported life because the ancient atmosphere had more carbon dioxide and therefore trapped more solar heat.27... 

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. 

Mars s gravity is weaker than Earth s, and the planet has been unable to retain much of an atmosphere. The Martian atmosphere is less than 1% as dense as Earth s, and is made mostly of carbon dioxide, with trace amounts of nitrogen and argon. 

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. 

The availability of space-based observatories, beginning in the 1960s, provided a new and promising way of collecting further data about the composition of the Martian atmosphere. A number of the early U.S. and USSR flights confirmed earlier Earth-based discoveries and provided new values for previously calculated variables. For example, both USSR Mars and U.S. Mariner spacecraft confirmed the concentrations of carbon dioxide and water vapor in the planet s atmosphere, and Mariner confirmed the general distribution of water vapor at various locations above the planet s surface and at various seasons. 

The atmosphere on Mars is composed mainly of carbon dioxide. The surface temperature is 220 K and the atmospheric pressure is about 6.0 mmHg. Taking... 

Earth is unique among the planets of our solar system in having an atmosphere that is chemically active and rich in oxygen. Mars, for example, has a much thinner atmosphere that is about 90 percent carbon dioxide. Jupiter, on the other hand, has no solid surface it is made up of 90 percent hydrogen, 9 percent helium, and 1 percent other substances. 

It is generally believed that the solar system condensed out of an interstellar cloud of gas and dust, referred to as the primordial solar nebula, about 4.6 billion years ago. The atmospheres of the Earth and the other terrestrial planets, Venus and Mars, are thought to have formed as a result of the release of trapped volatile compounds from the planet itself. The early atmosphere of the Earth is believed to have been a mixture of carbon dioxide (C02), nitrogen (N2), and water vapor (H20), with trace amounts of hydrogen (H2), a mixture similar to that emitted by present-day volcanoes. 

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