![]() | This article may be too technical for most readers to understand.(June 2012) |
Carbon dioxide hydrate or carbon dioxide clathrate is a snow-like crystalline substance composed of water ice and carbon dioxide. [1] It normally is a Type I gas clathrate. [2] There has also been some experimental evidence for the development of a metastable Type II phase at a temperature near the ice melting point. [1] [3] [4] The clathrate can exist below 283K (10 °C) at a range of pressures of carbon dioxide. CO2 hydrates are widely studied around the world due to their promising prospects of carbon dioxide capture from flue gas and fuel gas streams relevant to post-combustion and pre-combustion capture. [5] [6] [7] [8] It is also quite likely to be important on Mars due to the presence of carbon dioxide and ice at low temperatures.
The first evidence for the existence of CO2 hydrates dates back to the year 1882, when Zygmunt Florenty Wróblewski [9] [10] [11] reported clathrate formation while studying carbonic acid. He noted that gas hydrate was a white material resembling snow and could be formed by raising the pressure above a certain limit in his H2O - CO2 system. He was the first to estimate the CO2 hydrate composition, finding it to be approximately CO2•8H2O. He also mentions that "...the hydrate is only formed either on the walls of the tube, where the water layer is extremely thin or on the free water surface... (from French)" This already indicates the importance of the surface available for reaction (i.e. the larger the surface the better). Later on, in 1894, M. P. Villard deduced the hydrate composition as CO2•6H2O. [12] Three years later, he published the hydrate dissociation curve in the range 267 K to 283 K (-6 to 10 °C). [13] Tamman & Krige measured the hydrate decomposition curve from 253 K down to 230 K in 1925 [14] and Frost & Deaton (1946) determined the dissociation pressure between 273 and 283 K (0 and 10 °C). [15] Takenouchi & Kennedy (1965) measured the decomposition curve from 45 bars up to 2 kbar (4.5 to 200 MPa). [16] The CO2 hydrate was classified as a Type I clathrate for the first time by von Stackelberg & Muller (1954). [17]
On Earth, CO2 hydrate is mostly of academic interest. Tim Collett of the United States Geological Survey (USGS) proposed pumping carbon dioxide into subsurface methane clathrates, thereby releasing the methane and storing the carbon dioxide. [18] As of 2009, ConocoPhillips is working on a trial on the Alaska North Slope with the US Department of Energy to release methane in this way. [19] [18] At first glance, it seems that the thermodynamic conditions there favor the existence of hydrates, yet given that the pressure is created by sea water rather than by CO2, the hydrate will decompose. [20] Recently, Professor Praveen Linga and his group in collaboration with ExxonMobil have demonstrated the first-ever experimental evidence of the stability of carbon dioxide hydrate in deep-oceanic sediments. [21] [22] [23]
However, it is believed that CO2 clathrate might be of significant importance for planetology. CO2 is an abundant volatile on Mars. It dominates in the atmosphere and covers its polar ice caps much of the time. In the early seventies, the possible existence of CO2 hydrates on Mars was proposed. [24] Recent consideration of the temperature and pressure of the regolith and of the thermally insulating properties of dry ice and CO2 clathrate [25] suggested that dry ice, CO2 clathrate, liquid CO2, and carbonated groundwater are common phases, even at Martian temperatures. [26] [27] [28]
If CO2 hydrates are present in the Martian polar caps, as some authors suggest, [29] [30] [31] [27] then the polar cap can potentially melt at depth. Melting of the polar cap would not be possible if it was composed entirely of pure water ice (Mellon et al. 1996). This is because of the clathrate's lower thermal conductivity, higher stability under pressure, and higher strength, [32] as compared to pure water ice.
The question of a possible diurnal and annual CO2 hydrate cycle on Mars remains, since the large temperature amplitudes observed there cause exiting and reentering the clathrate stability field on a daily and seasonal basis. The question is, then, can gas hydrate being deposited on the surface be detected by any means? The OMEGA spectrometer on board Mars Express returned some data, which were used by the OMEGA team to produce CO2 and H2O-based images of the South polar cap. No definitive answer has been rendered with respect to Martian CO2 clathrate formation. [33]
The decomposition of CO2 hydrate is believed to play a significant role in the terraforming processes on Mars, and many of the observed surface features are partly attributed to it. For instance, Musselwhite et al. (2001) argued that the Martian gullies had been formed not by liquid water but by liquid CO2, since the present Martian climate does not allow liquid water existence on the surface in general. [34] This is especially true in the southern hemisphere, where most of the gully structures occur. However, water can be present there as ice Ih, CO2 hydrates or hydrates of other gases. [35] [36] All these can be melted under certain conditions and result in gully formation. There might also be liquid water at depths >2 km under the surface (see geotherms in the phase diagram). It is believed that the melting of ground-ice by high heat fluxes formed the Martian chaotic terrains. [37] Milton (1974) suggested the decomposition of CO2 clathrate caused rapid water outflows and formation of chaotic terrains. [38] Cabrol et al. (1998) proposed that the physical environment and the morphology of the south polar domes on Mars suggest possible cryovolcanism. [39] The surveyed region consisted of 1.5 km-thick-layered deposits covered seasonally by CO2 frost [40] underlain by H2O ice and CO2 hydrate at depths > 10 m. [24] When the pressure and the temperature are raised above the stability limit, clathrate is decomposed into ice and gases, resulting in explosive eruptions.
Still a lot more examples of the possible importance of the CO2 hydrate on Mars can be given. One thing remains unclear: is it really possible to form hydrate there? Kieffer (2000) suggests no significant amount of clathrates could exist near the surface of Mars. [41] Stewart & Nimmo (2002) find it is extremely unlikely that CO2 clathrate is present in the Martian regolith in quantities that would affect surface modification processes. [42] They argue that long term storage of CO2 hydrate in the crust, hypothetically formed in an ancient warmer climate, is limited by the removal rates in the present climate. [42] Baker et al. 1991 suggests that, if not today, at least in the early Martian geologic history the clathrates may have played an important role for the climate changes there. [43] Since not too much is known about the CO2 hydrates formation and decomposition kinetics, or their physical and structural properties, it becomes clear that all the above-mentioned speculations rest on extremely unstable bases.
On Enceladus decomposition of carbon dioxide clathrate is a possible way to explain the formation of gas plumes. [44]
In Europa (moon), clathrate should be important for storing carbon dioxide. In the conditions of the subsurface ocean in Europa, carbon dioxide clathrate should sink, and therefore not be apparent at the surface. [44]
The hydrate structures are stable at different pressure-temperature conditions depending on the guest molecule. Here is given one Mars-related phase diagram of CO2 hydrate, combined with those of pure CO2 and water. [45] CO2 hydrate has two quadruple points: (I-Lw-H-V) (T = 273.1 K; p = 12.56 bar or 1.256 MPa) and (Lw-H-V-LHC) (T = 283.0 K; p = 44.99 bar or 4.499 MPa). [2] CO2 itself has a triple point at T = 216.58 K and p = 5.185 bar (518.5 kPa) and a critical point at T = 304.2 K and p = 73.858 bar (7.3858 MPa). The dark gray region (V-I-H) represents the conditions at which CO2 hydrate is stable together with gaseous CO2 and water ice (below 273.15 K). On the horizontal axes the temperature is given in kelvins and degrees Celsius (bottom and top respectively). On the vertical ones are given the pressure (left) and the estimated depth in the Martian regolith (right). The horizontal dashed line at zero depth represents the average Martian surface conditions. The two bent dashed lines show two theoretical Martian geotherms after Stewart & Nimmo (2002) at 30° and 70° latitude. [42]
Methane clathrate (CH4·5.75H2O) or (4CH4·23H2O), also called methane hydrate, hydromethane, methane ice, fire ice, natural gas hydrate, or gas hydrate, is a solid clathrate compound (more specifically, a clathrate hydrate) in which a large amount of methane is trapped within a crystal structure of water, forming a solid similar to ice. Originally thought to occur only in the outer regions of the Solar System, where temperatures are low and water ice is common, significant deposits of methane clathrate have been found under sediments on the ocean floors of the Earth (approx. 1100m below the sea level). Methane hydrate is formed when hydrogen-bonded water and methane gas come into contact at high pressures and low temperatures in oceans.
Clathrate hydrates, or gas hydrates, clathrates, or hydrates, are crystalline water-based solids physically resembling ice, in which small non-polar molecules or polar molecules with large hydrophobic moieties are trapped inside "cages" of hydrogen bonded, frozen water molecules. In other words, clathrate hydrates are clathrate compounds in which the host molecule is water and the guest molecule is typically a gas or liquid. Without the support of the trapped molecules, the lattice structure of hydrate clathrates would collapse into conventional ice crystal structure or liquid water. Most low molecular weight gases, including O2, H2, N2, CO2, CH4, H2S, Ar, Kr, Xe, and Cl2 as well as some higher hydrocarbons and freons, will form hydrates at suitable temperatures and pressures. Clathrate hydrates are not officially chemical compounds, as the enclathrated guest molecules are never bonded to the lattice. The formation and decomposition of clathrate hydrates are first order phase transitions, not chemical reactions. Their detailed formation and decomposition mechanisms on a molecular level are still not well understood. Clathrate hydrates were first documented in 1810 by Sir Humphry Davy who found that water was a primary component of what was earlier thought to be solidified chlorine.
Dry ice colloquially means the solid form of carbon dioxide. It is commonly used for temporary refrigeration as CO2 does not have a liquid state at normal atmospheric pressure and sublimes directly from the solid state to the gas state. It is used primarily as a cooling agent, but is also used in fog machines at theatres for dramatic effects. Its advantages include lower temperature than that of water ice and not leaving any residue (other than incidental frost from moisture in the atmosphere). It is useful for preserving frozen foods (such as ice cream) where mechanical cooling is unavailable.
The atmosphere of Mars is the layer of gases surrounding Mars. It is primarily composed of carbon dioxide (95%), molecular nitrogen (2.85%), and argon (2%). It also contains trace levels of water vapor, oxygen, carbon monoxide, hydrogen, and noble gases. The atmosphere of Mars is much thinner and colder than Earth's having a max density 20g/m3 with a temperature generally below zero down to -60 Celsius. The average surface pressure is about 610 pascals (0.088 psi) which is 0.6% of the Earth's value.
The terraforming of Mars or the terraformation of Mars is a hypothetical procedure that would consist of a planetary engineering project or concurrent projects aspiring to transform Mars from a planet hostile to terrestrial life to one that could sustainably host humans and other lifeforms free of protection or mediation. The process would involve the modification of the planet's extant climate, atmosphere, and surface through a variety of resource-intensive initiatives, as well as the installation of a novel ecological system or systems.
The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) was a visible-infrared spectrometer aboard the Mars Reconnaissance Orbiter searching for mineralogic indications of past and present water on Mars. The CRISM instrument team comprised scientists from over ten universities and was led by principal investigator Scott Murchie. CRISM was designed, built, and tested by the Johns Hopkins University Applied Physics Laboratory.
Planum Australe is the southern polar plain on Mars. It extends southward of roughly 75°S and is centered at 83.9°S 160.0°E. The geology of this region was to be explored by the failed NASA mission Mars Polar Lander, which lost contact on entry into the Martian atmosphere.
The climate of Mars has been a topic of scientific curiosity for centuries, in part because it is the only terrestrial planet whose surface can be easily directly observed in detail from the Earth with help from a telescope.
Swiss cheese features (SCFs) are curious pits in the south polar ice cap of Mars named from their similarity to the holes in Swiss cheese. They were first seen in 2000 using Mars Orbiter Camera imagery.
The formation of carbonates on Mars have been suggested based on evidence of the presence of liquid water and atmospheric carbon dioxide in the planet's early stages. Moreover, due to their utility in registering changes in environmental conditions such as pH, temperature, fluid composition, carbonates have been considered as a primary target for planetary scientists' research. However, since their first detection in 2008, the large deposits of carbonates that were once expected on Mars have not been found, leading to multiple potential explanations that can explain why carbonates did not form massively on the planet.
Martian geysers are putative sites of small gas and dust eruptions that occur in the south polar region of Mars during the spring thaw. "Dark dune spots" and "spiders" – or araneiforms – are the two most visible types of features ascribed to these eruptions.
Methane is a chemical compound with the chemical formula CH4. It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes it an economically attractive fuel, although capturing and storing it is difficult because it is a gas at standard temperature and pressure. In the Earth's atmosphere methane is transparent to visible light but absorbs infrared radiation, acting as a greenhouse gas. Methane is an organic compound, and among the simplest of organic compounds. Methane is also a hydrocarbon.
The Mare Australe quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Mare Australe quadrangle is also referred to as MC-30. The quadrangle covers all the area of Mars south of 65°, including the South polar ice cap, and its surrounding area. The quadrangle's name derives from an older name for a feature that is now called Planum Australe, a large plain surrounding the polar cap. The Mars polar lander crash landed in this region.
Almost all water on Mars today exists as polar permafrost ice, though it also exists in small quantities as vapor in the atmosphere.
The planet Mars has two permanent polar ice caps of water ice and some dry ice (frozen carbon dioxide, CO2). Above kilometer-thick layers of water ice permafrost, slabs of dry ice are deposited during a pole's winter, lying in continuous darkness, causing 25–30% of the atmosphere being deposited annually at either of the poles. When the poles are again exposed to sunlight, the frozen CO2 sublimes. These seasonal actions transport large amounts of dust and water vapor, giving rise to Earth-like frost and large cirrus clouds.
Martian gullies are small, incised networks of narrow channels and their associated downslope sediment deposits, found on the planet of Mars. They are named for their resemblance to terrestrial gullies. First discovered on images from Mars Global Surveyor, they occur on steep slopes, especially on the walls of craters. Usually, each gully has a dendritic alcove at its head, a fan-shaped apron at its base, and a single thread of incised channel linking the two, giving the whole gully an hourglass shape. They are estimated to be relatively young because they have few, if any craters. A subclass of gullies is also found cut into the faces of sand dunes, that are themselves considered to be quite young. Linear dune gullies are now considered recurrent seasonal features.
Chaos terrain on Mars is distinctive; nothing on Earth compares to it. Chaos terrain generally consists of irregular groups of large blocks, some tens of kilometers across and a hundred or more meters high. The tilted and flat topped blocks form depressions hundreds of metres deep. A chaotic region can be recognized by a rat's nest of mesas, buttes, and hills, chopped through with valleys which in places look almost patterned. Some parts of this chaotic area have not collapsed completely—they are still formed into large mesas, so they may still contain water ice. Chaos regions formed long ago. By counting craters and by studying the valleys' relations with other geological features, scientists have concluded the channels formed 2.0 to 3.8 billion years ago.
Nitrogen clathrate or nitrogen hydrate is a clathrate consisting of ice with regular crystalline cavities that contain nitrogen molecules. Nitrogen clathrate is a variety of air hydrates. It occurs naturally in ice caps on Earth, and is believed to be important in the outer Solar System on moons such as Titan and Triton which have a cold nitrogen atmosphere.
The reported presence of methane in the atmosphere of Mars is of interest to many geologists and astrobiologists, as methane may indicate the presence of microbial life on Mars, or a geochemical process such as volcanism or hydrothermal activity.
Mars's atmosphere is predominantly composed of CO2 (around 95%) with seasonal air pressure change that facilitates the vaporization and condensation of carbon dioxide. The CO2 cycle on the planet Mars has facilitated the formation of CO2 ice clouds at various locations and seasons on the red planet. Due to low temperatures, especially at Mars's polar caps, carbon dioxide gas can freeze in Mars’s atmosphere to form ice crystallized clouds. Several missions, such as the Viking, Mars Global Surveyor, and Mars Express, have led to interesting observations and measurements regarding CO2 ice clouds. MOLA data in addition to TES spectra have documented ice clouds forming during the winter season of Mars’s northern and southern polar caps. In addition, the Curiosity rover has imaged clouds well above 60 kilometers in the sky at the planet’s equator during the coldest time of Mars’s orbital year (when Mars is furthest away from the Sun due to its elliptical orbit), indicating the possibility of CO2 ice clouds around the planet’s equator. Although further data collection is needed to confirm the formation of CO2 ice clouds on Mars, especially at the planet’s equator, previous measurements have developed a strong argument for frozen carbon dioxide clouds on Mars.