Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
32 Cards in this Set
- Front
- Back
|
Statistics. |
- fourth planet from Sun, ∼50% farther than Earth, and last of inner/terrestrial planets. - rotates on axis (Mars day) every 24 1/2 hours, and revolves around Sun (Mars year) in 1.88 Earth years. - axis of rotation inclined 24° from normal to ecliptic - diameter = 6,790 km ~1⁄2 of Earth’s. - density = 3.93 cm3 (5.52 g/cm3 for Earth). - thin atmosphere, with a pressure of only 6mb (earth at 1000mb), dominated by co2 (at least 95%, with lesser N2, H2O at O2, and air). - surface temperature = 150 - 300 K (-123 - 27° C). - Mars Global Surveyor, over a year spanning 1997/98, noted wind storms with wind speeds as big as 580 km/h, almost 5 times minimum for hurricane on earth. - suspended dust in Martian atmosphere heats up very rapidly, temperature rising by 7°C just after sunrise; captured heat triggers growth of vortices, may cover vast areas - no magnetic field (field strength <0.01% Earth’s); it is a weak remanding field in Martian crust from warmer period in history when it would've had an active field |
|
|
Internal Structure. |
- much larger than Mercury but much lower density, which is not surprising (formed much farther from Sun in region of lower temp=lighter condensates) - structure is comparable to that of Earth - surface rocks are less dense than planet’s average, it likely has iron core (perhaps with S, O) of 1500 - 2000 km radius, that is now solid. - mantle is calculated to be 1300-1800 km thick, and understood to be convecting. - crustal thickness from as little as 3 km to as much as 90 km, with average of 50 km; composition known from SNC meteorites recent orbiters, and landers. - a particular pair of meteorites, NWA 7034 and NWA 7533 believed to be representative of “average” Martian crust. basaltic breccias, with fragments of volcanic rocks in matrix of basaltic material, may represent melt sheet materials. - early basaltic crustal material has been weathered, eroded, and redistributed by winds, to blanket Mars with red soil/dust that gives geochemical signature that matches Martian basaltic breccias. - subtle differences between analyses and SNC meteorites: SNC groups lack of subsequent interaction with Martian atmosphere. |
|
|
Densely Cratered Highlands. |
- comprise southern hemisphere; similar to ancient cratered terrains of moon and Mercury. - several large, multiring impact basins; Hellas at 2000 km exceeds even Imbrium and Caloris Basins. - represent: preserved ancient crustal surface, almost certainly older than 4.0 G.a. - although some craters show classic rays & secondary cratering, many show evidence of flow of ejecta, suggesting involvement of water. - rampart or splash craters: wherein ejecta moved as heavy mudflows, with lobate flow fronts having steep or rampart faces, rather than airborne Rays. - continuous ejecta deposit extends 1.5 to 2X crater radius, vs. typical values of 0.7 for Moon, and 0.5 for Mercury. - model explaining formation: impact melts ice & liquid mixes with ejecta to form a slurry (like lahars or mudflows related to volcanic episodes) - distribution of such craters might allow mapping of ground ice/groundwater variation, and smallest size of rampart crater might reveal minimum depth to H2O. |
|
|
Northern Plains |
- dominate northern hemisphere, separated from southern highlands by an escarpment that is 2-3 km high. - mare-type basalts, organic features, stream-borne sediments, & evidence of aeolian activity. - upon arrival in 1971, Mariner couldn’t see surface due to global dust storm; various sources give differing numbers e.g. wind speeds 200 km/h or more, Viking landers recorded wind speeds 108 km/h, up to 500 km/h. - depositional features: dunes and dune fields of sand-size dark grains: (rather than Quartz as on earth; unavailable, and security not an issue), some seasonally covered by north polar ice cap,. erosional features: yardangs - sculpted ridges produced by removal of less resistant material. |
|
|
Global Escarpment. |
- erosional contact between older southern and younger northern hemispheres; it encircles Mars with few interruptions. - speculated to have been produced by large scale impact (mechanism unknown – thinning of crust in north). - dissected by stream erosion and mass movement/slumping, there are isolated blocks/mesas just north in what is called fretted terrain. |
|
|
Crustal Upwarps. |
- two major, continent-sized upwarps occur in northern plains, named: Tharsis and Elysium. - Tharsis Uplift believed to have originated ~ 3.5 G.a., terminating ~2.3 G.a., as hot mantle material rose by convection (without accompanying plate motions, there being no plates; Mars cooled too quickly and lithosphere became too thick). - have shield volcanoes, lava flows, calderas, and radial fracture systems; basaltic composition seems likely (compared with SNC meteorites). - included is Olympus Mons, largest volcano in Solar System at 27 km height and 600 km diameter, located on Tharsis Uplift. - most recent activity on Olympus Mons remarkably free of cratering, leading to estimates of timing of eruptions: 200 m.y. to 10 m.y. Since last eruptions; clearly volcanic activity has carried on after termination of Tharsis Uplift formation. - twice largest on Earth; lack of plate tectonics on Mars, a single "mantle plume" operating over long span of time would generate single enormous volcano. - isotopic data suggests Mars has two reservoirs for basalts that separated early on, remaining unmixed due to absence of plate tectonics. |
|
|
Polar Regions. |
- water ice (h20) and dry ice (co2) in winter, polar temperatures reach 130k vs freezing point for co2 of 148k. - removal of CO2 by freezing causes drop in atmospheric pressure over winter pole; effect on atmospheric circulation: consists of a single Hadley cell where surface movement is from summer(H) to winter (L) hemisphere. - Glacier movement in poles? - “Yes” side: it is largely H2O ice, so it should be possible; peculiar spiral form to polar ice caps, suggestive of some kind of dynamic; deposits show overlap i.e. dynamic, not static. - “No” side: if it is CO2 ice it would be too brittle to flow/be plastic; even if H2O, caps are too thin and Martian gravitational field too weak for them to flow under own weight; spiral troughs would seal or open i.e. show change if there were flow; only 1 mm/y accumulates on polar cap. - Mars’ obliquity varies between 15 & 35°; small satellites Phobos and Deimos do not stabilize Mars obliquity. - Mars has its own “Milankovitch Cycles”. - from Mars Global Surveyor mission, Mars Orbiter Camera took photos in successive Martian years, (our years 1999 and 200)1, mission was extended beyond its primary mission of one Mars year, 687 Earth days. - intent was to take images to allow for stereo viewing, but features on south polar ice cap had changed. - rapid retreat of faces of scarps and pits in layered CO2 ice (only dry ice would be sufficiently volatile), rates averaging 3m per Mars year, in extreme reaching 8m per Mars year. - isolated pits grow to become valleys, broad mesas retreat to become isolated buttes; similar time scale for Earth’s climatic fluctuations, e.g. “Little Ice Age” mid-14th-mid-19th centuries; temperatures ~1-2° C colder. - fluctuations in CO2 ice cover may be responsible for features once attributed to flow of liquid water; dunes (before recent landforms) cut by gullies - noteworthy for having raised edges, & pits rather than sediment deposits at down-slope end, and remarkably straight path. - Hugenholtz (U of C) et al.: conditions prevent presence and flow of water, but that blocks of dry ice, detaching from blanket of CO2 frost, would ride down cushion of vaporizing CO2, as “hover ice”, to create gullies, plowing up ridges of sediment at sides. |
|
|
Volcanic Features. |
Volcanic Plains: - Martian basalts differ from terrestrial basalts, they appear to be enriched in K, Na (volatiles) Fe, and depleted Al compared to terrestrial basalts; given that Mars is supposed to have formed far from Sun - should be more volatile-rich. Patera: - large structures of low relief, often with central volcanoes & flows of vast extent, what appear to be pyroclastics (cinder cones, e.g.). - explosive activity may constitute form of phreatic eruption as ice goes to steam due to approach of magma/lava. - patera have associated tectonic features. |
|
|
Tectonic Features. |
Tectonic Features: - no evidence for plate tectonics; what we see are: Mare Ridges/Wrinkle Ridges. - produced by buckling of cooling lavas in volcanic plains. Canyons. - many fault structures/grabens related to crustal extensions as unwarps occurred. - Valles Marineris on Tharsis Dome: 4000 km long by 700 km wide by 7 km deep, comparable to East African Rift (divergent plate boundary on Earth). - Valles Marineris was produced in first instance by extensional tectonics, has been substantially modified by mass movements and fluvial erosion. |
|
|
Water on Mars: Viking, Polar Caps, & Dendritic Drainage Systems. |
Viking. - measured water in atmosphere, rocks and solids. polar caps. - are dominantly H2O ice, plus CO2. Dendritic drainage systems. - overland flow of precipitation, evidence of “sapping” - groundwater seepage and flow leads to enlargement of a channel which is structurally controlled,no apparent associated drainage basin. scarcity of tributary channels for even dendritic systems, suggesting limited overland flow, or possibly subsequent erosion of lesser channels (less likely). range from 4.5 - 3.5 G.a. |
|
|
Water on Mars: Outflow Channels & Freshly Exposed Ice Patches. |
Outflow channels. - running from southern highlands to northern plains across global escarpment, “unsourced” channels that evidently carried groundwater that first surfaced at springs, then flowed northward in braided stream systems with tremendous erosive power. - collapse or subsidence of overlying terrains into voids created by this loss of subsurface water. Freshly-exposed ice patches. – recent small-scale cratering (depth of excavation up to 2.5 m) exposes fresh, bright water ice that within weeks vaporizes to leave excavation dark. |
|
|
Water on Mars: Other Features. |
- Mars Pathfinder mission, 1997, detected water-related features by camera and X-ray spectrometer. - one hill exhibits four or five coloured bands or layers (similar to Grand Canyon stratigraphy), suggesting not just one episode of water flowing across planet’s surface. - piles of well-rounded boulders suggest rounding by stream flow, and also exhibit imbrication: boulders stacked tilting in same direction, indicative of very strong flow of water - rover Curiosity found stream bed, with rounded, “M&M-sized” pebbles; could not be moved/produced by wind. - a sample revealed equivalent chemistry to andesite, an intermediate composition volcanic rock characterized by significant water content, bound in minerals as part of basic chemistry (OH- or hydroxyl group) opposed to within pore spaces; suggests significant internal and early water, not just near-surface and possibly introduced from external sources. - Mars Reconnaissance Orbiter observed McLaughlin Crater, 92 km in diameter and 2.2 km deep, with layered carbonates and clays (CRISM spectrometry matches composition) normally deposited from aqueous media; no inflow channels breaching crater rim, suggesting crater’s lake was fed by groundwater. - Mars Rover Spirit, landed in Gusev Crater January 3, 2004, & Mars Rover Opportunity, landed on Meridiani Planum January 25, 2004; both generated tremendous numbers of images, and geochemical data sets. - Rover Spirit recorded sediment deposits equivalent to a delta entering standing body of water, at margin of crater. - Opportunity observed small concretions that have been called “blueberries” - hematite (Fe2O3), where they have been abraded, do not show concentric structure expected of concretions. - drilled into bedrock, analysis is equivalent of mineral jarosite, a K-Fe-sulphate-hydroxide which only form in presence of water. - within crater Endeavour, Opportunity detected fracture filling, “Homestake vein”, with calcium sulphate, most likely gypsum, CaSO4.2H2O, normally low-temperature precipitate from aqueous solutions. - suggested Mars outgassed enough h2O to cover surface to depth of 440m (Earth outgasses enough water to cover itself to depth of 2700m); - outflow of water from southern highlands cover have produced a northern ocean. - modeling/comparison of Venus, Earth, and Mars, from standpoint of surface temperatures due to distance from Sun, shows water accumulating in atmospheres until a particular pressure reached. - on Mars it would have gone to ice (bulk of Mars’ water believed to constitute cryosphere, likely upper 10 km of crust), on Earth was liquid, and on Venus would have eventually gone to liquid state, but remained in vapour state due to runaway greenhouse effect. - limitation of this model: evidence that Mars had significant liquid water, enabled by presence of dissolved chlorides (“brines”) lowering melting point i.e. not pure/fresh water. |
|
|
Life on Mars: Viking Mission. |
- two Viking landers carried out experiments designed to find evidence of life in terms of chemical effects rather than direct evidence. - search was for any indication that organisms released gas as by-product of metabolic activity, be it respiration or use of nutrients, or would incorporate tagged isotopes in cells, to be detected by pyrolysis. - results were not inconsistent with biological activity, but were better explained by abiotic means. - Scientists regarded as unlikely that any organisms would withstand heating to 93 °C, let alone 180°C (there are no high temperatures on Mars which thermophiles would adapt); concluded some abiotic process was involved. |
|
|
The best argument against an asthenosphere on mars is? |
Absence of convergent plate tectonic features |
|
|
The oldest rocks on the moon are? |
Anorthosite. |
|
|
Which is not evidence for water on Mars? A. Anorthosite composition rocks. B. Canyons. C. Rampart craters. D. All of the above. |
A. Anorthosite composition rocks. |
|
|
Which does not support collision model of the Moon? A. Earth’s density. B. Excess volatiles on the moon. C. Orbital relationship. D. Oxygen isotope ratios. |
B. Excess volatiles on the moon. |
|
|
The fretted terrains on Mars are produced by? A. Cratering & slumping. B. Cratering & stream erosion. C. Slumping & stream erosion D. Stream erosion & volcanic eruption. |
C. Slumping & stream erosion |
|
|
Martian Meteorite. |
- a 1.9 kg sample collected from Antarctica in 1984, recognized as Martian in 1994. - reported as 1 of 13 samples that belong to a class called SNC meteorites; this one differs petrologically from S, N, & C types. - sample: Allan Hills (ALH) 84001, an igneous orthopyroxenite that crystallized 4.5 Ga. - two episodes of shock have affected sample; first: estimated at 4.0 Ga, produced multiple fractures whose surfaces have carbonate “globules” up to 250 μm in diameter. - second: affected/disrupted carbonate globules, which are estimated to be 3.6 G.a. in age - timing of sample’s excavation from Mars: 16 m.y.a. arrival on Earth: 13,000 y.p.b. - two questions we need to ask are: i. is evidence or material indigenous or terrestrial contaminant?
ii. material biogenic, inorganic, or possibly either? |
|
|
Polycyclic Aromatic Hydrocarbons (PAH). |
- various hydrocarbons, whose occurrence is as fossil molecules in sedimentary rocks, coal, and petroleum; exhibit tremendous variety, numbered in 1000’s, and produced by chemical aromatization. - sample ALH 84001: relatively few and simple PAH, the four most abundant are simple ring hydrocarbons; produced by early diagenesis (alteration at lower temperatures than metamorphism). - interior fracture surfaces in sample average >1 ppm PAH, levels are highest in vicinity of carbonate globules. - Contaminants? PAH accumulation over past 400 years has been studied in Greenland ice cores, i.e. 103-105 times lower than measured concentrations in ALH 84001. - PAH from Greenland mostly anthropogenic, with a particular peak, at 184 amu - Weathered Antarctic meteorites show no terrestrial PAH within detection limits, neither do uncontaminated non-Martian meteorites. - examination of meteorite ALH 84001 shows that outer 500 μm (0.5 mm) of sample exhibit a lack of PAH, a pattern which is consistent with this being a fusion crust or zone, formed upon entry into Earth’s atmosphere, heat of friction causing pyrolysis (burning) or volatilization (evaporation) of indigenous PAH from near surface of sample. - if PAH in sample were contaminants, concentrations expected to be higher near surface of sample, than depleted as they are. - conclusion: PAH belong to sample, and not been introduced since arrival on Earth. |
|
|
Criticisms of Polycyclic Aromatic Hydrocarbons (PAH). |
- abiotic organic matter can also undergo same aromatization, (methane to naphthalene) (a PAH); simply the way in which C, H, and O form most stable product at certain temperature & in certain proportions. - close association of PAH with carbonate globules may have no biotic significance; finer-grained carbonate (compared to minerals in meteorite) could have been an adsorbant, which scavenged carbonaceous material from environment; ferric oxide that gives globules orange colour is a catalyst in aromatization. - PAH of similar character are found in certain classes of chondrites for which no biotic origin is suggested. |
|
|
Carbonate Globules. |
- on Earth, production of significant volumes of carbonate minerals generally requires biological activity or mediation, hence attraction of carbonate globules as evidence of biological activity on Mars. - a sequence in chemistry, working from globule interiors to outer surfaces, of Ca (+Mn) carbonates, then Fe carbonate, then Fe sulphides, consistent with terrestrial low-temperature biomineralization. - carbonate exhibits dissolution, whereas associated magnetite and iron sulphides don’t; suggested that organic activity required to maintain disequilibrium (all three are soluble at acid or low pH conditions). - stable oxygen isotope ratios suggest low temperatures of formation (0-80° C). Caution: different species will exhibit different ratios at same temperature. |
|
|
Criticisms of Carbonate Globules. |
- carbonaceous chondrites with carbonate materials show similar sequences of chemistry in accepted abiotic conditions. - carbonate dissolution may occur at pH as high as 5.3, pH will rise rapidly to pH 6 or higher; level of disequilibrium and biological mediation; all values are too high for dissolution of magnetite or iron sulphides, thus no real disequilibrium here, and no need for biological mediation of system to produce observations. - petrographic and electron microprobe studies suggest that carbonate is of high temperature origin, (high as 700° C); may be too high for biological activity. |
|
|
Cellular Bodies/Surface Features. |
- some carbonate grains have small, ovoid to elongate bodies on surfaces; 20-80 nm across, and as much as 100 nm long and interpreted to be preserved cellular outlines. - not artifacts produced by couple of known possibilities: by coating of samples for SEM examination, nor by etching of sample (expected to follow more geometric pattern of crystal lattice). |
|
|
Criticisms of Cellular Bodies/Surface Features. |
- these bodies are 100X smaller than smallest known microfossils; authors responded by noting nanobacterium that measures 200X400 nm, which is in right size range; critics respond by questioning validity of nanobacterium. - maximum number of atoms that could fit inside a cell this size is less than 100X106, too low for functioning cell. - Schopf (1996, reported in Goldsmith, 1997, p. 189) suggested bodies needed to meet certain criteria to be considered biological: high number (500+) cell walls, cell division and log normal/ bell curve distribution plus variation in shape. |
|
|
Criticisms of Sulphur Isotopes & Evaluation. |
- terrestrial biologic systems or activity fractionate S isotopes (i.e. preferentially handle one over other; thus, sulphate-reducing bacteria excrete H2S enriched in 32S vs. 34S. - pyrite (FeS2) grains within carbonate globules, supposed sites of biological activity, enriched in 34S instead, by 4.8 - 7.8 permil; suggestive of low-temperature, non-biologic origin. - we cannot assume that Martian life would fractionate in same fashion, nor can we prove that pyrite grains are contemporaneous with their small bodies or carbonate globules. Evaluation. - evidence may be consistent with biologic activity, neither diagnostic nor compelling. |
|
|
Postscripts/Further Work. |
- a source showed results of subsequent investigations of small bodies in sample ALH 84001; no internal structure or subdivision, i.e. no hint of organic construction. - Nakhla meteorite (“N” in SNC) reveals round and ovoid bodies as in ALH 84001, many larger than those from ALH 84001, being a few hundred nm (few tenths of a micron), and thus more plausible as bacteria or microbes; recovery of samples was almost immediate, in case of fragment studied by McKay, came from fusion crust opened in sterile environment, thus uncontaminated. - ALH 84001 contains many microscopic crystals of magnetite (Fe3O4); a quarter of se are in form of chemically pure, perfectly shaped and same-sized hexagonal prisms. - in terrestrial settings, such crystals are produced only by bacteria that use as means to orient in Earth’s magnetic field; not produced by any known inorganic process. - Shergotty meteorite (age 165 m.y.a.) shows “suspicious” features; if valid, suggests a significant span to life on Mars. |
|
|
Most of the water on mars is in what state? A. liquid. B. solid. C. vapour/gas. D. it has no water. |
B. solid. |
|
|
Rayer craters are characteristic of what lunar period? A. Copernican. B. Eratosthenian. C. Imbrian. D. Nectarian. |
A. Copernican. |
|
|
Compared to mean radius of the moon, A. both maria and terrae are higher. B. maria are higher, and terrae lower. C. maria are lower, and terrae higher. D. both maria and terrae are lower. |
C. maria are lower, and terrae higher. |
|
|
Modeling suggests early in its history, water on Mars should have been in? A. liquid state. B. solid state. C. vapour state. D. all three states, as on Earth. |
B. solid state. |
|
|
Which of following craters/basins on Moon is youngest? A. Copernicus. B. Imbrium. C. Nectaris . D. Tycho. |
D. Tycho. |
