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26 Cards in this Set
- Front
- Back
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The Moon: The Basics & Statistics. |
- satellite of Earth; differentiated planetary body in its own right. - exert significant gravitational attraction on each other, causing both to have a slightly elliptical shape. - the Moon’s pull on Earth produces ocean tides and Earth tides. - rotates on axis every 27.3 Earth days, revolves around Earth in 27.3 days: same side of Moon faces Earth always. - diameter = 3480 km (12,700 for Earth). - density = 3.34 g/cm3 (5.52 g/cm3 for Earth) - no liquid water, no atmosphere, no surface pressure. - temperature range = 100-400 K (-173 to 130° C). - strength of gravitational field at surface is 16% of Earth’s. - no magnetic field. |
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Mechanics of the Earth-Moon System |
- dynamic: changes over geologically significant spans of time. - distortion of Earth’s shape by pull of the Moon can’t keep pace with Earth’s rotational speed; excess mass associated with its bulge is not aligned on earth-moon axis. - bulge on the Earth & Moon attract, Earth’s rotational speed decreases, and Moon’s orbital velocity increases; makes Moon retreat from the Earth over time. - Apollo astronauts placed reflectors on moon; reflect laser beams from Earth and measure distance between Earth & Moon within 1 cm. - Moon is retreating from Earth at the rate of 4 cm/yr - Earth’s rotation slowing - problematic. |
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Internal Structure.
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- usual remote measurements of basic properties, direct sampling of surface rocks, seismic data - seismometers recording “Moon quakes”.
- 6 Apollo missions, 3 Soviet landers (1969-1975), - recovered over 380 kg of rocks in 2000 samples, including 160 cm long core. - NASA’s GRAIL (Gravity Recovery and Interior Laboratory) mission: pair of probes, Ebb & Flow - precise gravitational survey shows Moon’s crust to range from 34-43 km thick & revealed presence of dikes. - base of crust marked by significant increase in seismic velocity: Moonquakes - crust is heavily shattered for first few km, fracturing & brecciation to depths of ∼25 km - impacting by bolides. - mantle materials to 1000 km depth, + crust comprises lithosphere; Moonquakes originate near base of mantle or lithosphere, (800 km): result of tidal stresses caused by gravitational pull between Earth, Moon & Sun. - weak propagation of seismic S-waves below this depth implies an asthenosphere (plastic, low-velocity layer). - reanalysis of Apollo seismic data confirmed Moon has an iron rich core. radius = 330 ± 20 km. - lunar rock samples reveal remanent magnetism, date 3.9 - 3.1 Ga, coincident with eruption of mare basalts |
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Surface Geology.
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A. Terrae/highlands - rough highland or mountainous region, relatively high albedo.
- up to 5 km above mean planet radius (MPR), dated: ~4.56 - 4.4 G.a.; consistent greater age indicated by higher crater density B. Maria/Mare - large, dark plains - lie ~5 km below MPR, dated: 3.9 and 3.1 G.a., consistent with lower density of impact craters |
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Impact Craters. |
- sequence worked out by superposition & crosscutting of rims + radiometric dating = absolute timing
- dating indicates: moon is 4.53 G.a. - young crater, Copernicus = 0.8 G.a. - crater degradation = process where a simple crater changes through time, occurs by: i. Volcanism ii. Stream erosion iii. Impacts iv. Ejecta blanketing v. Moonquakes vi. Slumping |
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Volcanic Features.
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- lava flows extending over 600 km at slopes low as 1%, lobate flow fronts like terrestrial flood basalts from fissure eruptions: linear volcanic vent through which lava erupts, usually without any explosive activity - Mare basins: are large, dark, basaltic plains formed by ancient volcanic eruptions - very low viscosity - sinuous rilles/lava channels: 100+ km long, 1+ km wide, few 100 m deep - mark lava channels or collapsed lava tubes that formed during mare volcanism - all related to extrusion of mare basalts, 3.9 - 3.1 G.a. - few volcanic domes also seen & basaltic pyroclastic volcanoes (resemble Earth’s cinder cones) - evidence of water molecules trapped in volcanic glass beads |
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Anorthosite. |
- an igneous rock, almost pure plagioclase feldspar, especially CaAl2Si2O8.
- dominant constituent of lunar highlands: the oldest rocks, >4.4 G.a., predations eruption of mare basalts, and meteorite bombardment. - Moon’s early thermal state = outer layer molten, magma ocean with particular features developing: top of which early formed Ca-plagioclase would rise, to form primitive crust as coalesced "rockbergs"; earliest lunar crust. |
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Basalts. |
- volcanic rocks that comprise maria.
- similar to basalts on Earth except for certain features: complete absence of water/other coalitions, lesser K and Na; higher concentration of refractory elements (e.g. Ti, Zr, and Cr) i.e. higher temperature of condensation for the moon as compared to earth. - some lunar basalts have vesicles: evidence of volatiles escaping from lava as it cooled. - two kinds of basalts: mare basalts, generally <3.9 G.a., likely produced by melting of mantle materials. - KREEP basalts [high in K, REE (rare earth elements), and P], produced by fractional crystallization from primitive magma ocean, OR partial melting of an early crust; dated at ~3.85 G.a., prior to formation of Imbrium Basin. |
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Lunar Glass Beads & Breccia. |
Lunar Glass Beads - collected by Apollo 17 astronauts, mostly spherical, produced by eruptive process: "fire fountaining"; date at 3.48 G.a. As lava rapidly boiled/spewed to surface, droplets of lava quenched very quick to produce beads; associated vapours included ZnCl2 and GaCl3. Breccia - produced by bolide impact, consists of angular fragments of rock/glass, solidified by shock /compression, or welding by hot, glassy materials. |
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Regolith & Glass. |
Regolith - ejecta not yet consolidated, mixture of debris. - thickness correlates with age of underlying rocks (e.g. young crater Tycho: 10 cm, maria average 5 m, highlands may have as much as 10 m). - cannot use linear interpolation or extrapolation of regolith thickness to calculate surface age, because frequency and concentration of cratering has diminished significantly through time. - includes agglutinates [“stuck togethers”], fragments coalesced rather than remain fragmented; in absence of an atmosphere or liquid water, agglutination process: welding by melt products of micrometeorite impacts. responsible for: ejecta ray blanket degradation from bright (rough surfaces) to dark (smoother surfaces). Glass - equivalent of melt rock, released by bolide impact. - samples from rays of Copernicus show 70-90% glass in ejecta. |
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Pre-Nectarian Period. |
- encompasses span of time from formation of Moon - formation of the Nectaris Basin, i.e. 4.56-3.92 G.a. - embraces a few steps: "accretion", melting of perhaps outer few 100km to form magma ocean, then formation of primitive lunar crust, preserved as anorthositic lunar highlands/terrae. - all has been modified by intense bombardment. |
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Nectarian Period. |
- contemporaneous with formation of nectar is basin on eastern side of moon, ~3.92-3.85 G.a. - surfaces this old have been subjected to much bombardment by great range of objects, coincides with great cratering period, Late Heavy Bombardment, or LHB. - may be impossible to distinguish between surfaces Nectarian vs. Pre-Nectarian, so may be united under single label, Pre-Imbrian). - over 40 impact basins known from this period with diameters in range of 300-1000 km. - what else happend at this time: KREEP basalts formed. |
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Imbrian & Eratosthenian Periods. |
Imbrian Period - spans from formation of aim rim basin, a huge multilingual impact basin on northwest part of moon, until termination of extrusion of mare basalts, thus 3.85 - 3.15 G.a. - mare basalts: formed by partial melting of moons peridotite mantle, 400+ km depth, with possible heat sources being radioactive decay or tidal friction (earth and moon were much closer together - tidal effects stronger). Eratosthenian Period - surfaces formed during this period sometimes hard to distinguish from older cratered surfaces; cratering: has no evident rays, ejecta deposits are dark, secondary craters subdued, compared to younger ones. - spans 3.15-1.1 G.a. - period is recognized: where craters impacted Maria (must be younger.) |
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Copernican Period. |
- formations and preservation of rayed craters and rim deposits, good secondary crater systems, time span = 1.1 G.a. - present. - examples are Copernicus (0.8 G.a.) and Tycho (0.4? G.a.). - Eratosthenian and Copernican represent same thing: geologically inactive moon, post-volcanic and post-tectonic. - distinction is somewhat arbitrary, but freshness of impact characterizes Copernican Period; both represent light meteorite bombardment. |
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Origin of the Moon: Fission from Earth, "Splitting the Atoms." |
- considering retreat of Moon from Earth, plus slowing of Earth’s rotation, early in its history, Earth was spinning quickly. - when the two bodies were together: ~6 hour period for Earth’s rotation, 4X present rate. - suggests high spin rate allowed material to be ejected from Earth, coalescing to form Moon. - to throw off material from Earth, the planet would have to spin with frequency equal to critical vibration frequency (wine glass effect). - Given earths mass, this would require 2hr period of rotation, not 6, highly unlikely to have occurred. |
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Origin of the Moon: Capture. |
- Earth’s gravitational field captured a satellite that formed elsewhere, requires highly improbable orbit for Moon prior to capture (“one-in-a-billion” chance.) - oxygen isotope evidence argues against this; different groups of meteorites (including those representing fragments of Mars) plot on different trends than Earth, reflecting distinct differences in their history; Moon plots same line as Earth, implying significant common history/origin. |
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Origin of the Moon: Binary Accretion. |
- Moon and Earth accreted as separate bodies from same reservoir of material in the conducing solar nebula. - most unlikely given compositional differences, namely: i. density – Moon’s bulk density is 3.34 g/cm3, compared to Earths (5.52), implying nearly complete absence of Fe-rich core. ii. volatiles – Moon is strongly depleted in volatile elements, implying a higher temp or origin. - another problem: Moon does not orbit Earth in ecliptic plane. |
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Origin of the Moon: Collision. |
- favoured model: Mars-Sized planetesimal (“Theia”) believed to have collided with Earth. - estimates of temperature run to extreme of 6000 K, produced by conversion of kinetic energy to heat. - excavation would have involved (crust plus) mantle material from Earth i.e. predominantly ultramafic silicates; this ultra hot debris would have cooled and condensed as an orbiting ring of debris which then accreted to form Moon. consistent with and explain many observations: i. Oxygen isotopes are same for Earth and Moon. ii. depletion of volatiles on Moon compared to other bodies. iii. Lack of Fe on Moon iv. tilt of Earth ’s rotational axis off expected 90 degree to ecliptic plane (currently 23 degrees) v. orbital relationship between Earth & Moon - period of Moons rotation and orbit are the same. vi. Earth has an apparent excess of Fe, Ni, in mantle, representing inhomogeneous accretion that accounts for anomalously high bulk density compared to Mercury and Venus; represents “core” or at least dense component of bolide. - estimates have suggested 80% probability of Earth being impacted by a body of this size. |
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Lunar Water/Ice - Lunar Prospector. |
- Lunar Prospector, launched January 6, 1998, with primary 1-year orbiting mission. - small craft, a graphite-epoxy drum 1.4 m X 1.2 m, with surface mounted solar cells; three masts @ 2.5 m, bearing a total of five instruments. - Prospector mapped an area ∼150 X 175 km on both poles of Moon; area is elliptical because craft is both orbiting and spinning. - preliminary analyses suggested somewhere between 10 and 300X106 tons of water ice; wide range is due to fact that this is first interplanetary mission to use neutron spectroscopy, and no good calibration of tool response to source; calculation could be off by an order of magnitude. |
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Lunar Water/Ice - Detecting Water. |
- neutron spectrometer can detect water ice (i.e hydrogen) down to a depth of ∼0.5 m, whereas models predict that meteorite and other bolide impacts have gardened/ploughed Moon’s surface to a depth of 2 m. - medium-emery neutrons emitted by Moon intercepted/retarded by lunar soil that contains wear (neutrons are almost same as H atoms) + strong dips/lows in neutron emission seen at both poles. - Higher-energy/fast neutrons would show strong dips or a negative response if water were concentrated as large chunks of ice. - no significant dips in counts of high-energy neutrons, implying water ice dispersed as small crystals, perhaps at mixing ratio of 0.3 to 1.0%, over an area of 5,000 - 20,000 km2 at south pole, and 10,000 - 50,000 km2 at north pole. - water presumed to have been introduced by commentary sources, rather than begin indigenous.
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Lunar Water/Ice - Recent Research. |
- recently, LCROSS mission [Lunar CRater Observation and Sensing Satellite] companion to Lunar Reconnaissance Orbiter (LRO), launched June 18, 2009, impacted lunar surface on October 9, 2009. - result: produced plume that confirmed presence of water ice on Moon; plume rose almost 16 km above lunar surface, contained enough water to suggest over 5% concentration in soils, showed almost 20% of excavated martial to be various volatiles. - Hui et al. (2013) reinvestigated a lunar sample recovered by Apollo 15 mission in 1971; this troctolite, ~4.5 G.a. dubbed “Genesis Rock”, had up to 12 p.p.m. “water” in form of hydroxyl group. - water in Moon’s history not so volatile-depleted as once thought. - Hui et al. estimated that if troctolite crystallized after flotation from magma ocean, “ocean” could have had as much as 320 p.p.m. water. |
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Bulk Density of the Moon is closet to: A. 3.0 g/cm3. B. 4.0 g/cm3. C. 5.0 g/cm3. D. 6.0 g/cm3. |
A. 3.0 g/cm3 |
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Which of the following statements is true? A. The moon is nearing the Earth and velocity decreasing. B. Nearing the earth and velocity increasing. C. Moon is retreating and velocity decreasing. D. Moon is retreating and velocity increasing . |
D. Moon is retreating and velocity increasing. |
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Which of the following rocks is not part of the lunar crust? A. anorthosite. B. basalt. C. gabbro. D. peridotite. |
D. Peridotite. |
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Which of following lunar features is produced by volcanism? A. linear rilles. B. sinuous rilles. C. wrinkle ridges. D. none of the above. |
B. Sinuous Rilles |
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temperature on the sunward side of the Moon can reach 400K. in C, this is equal to? A. -173. B. - 127. C. 212. D. 273. |
B. -127 |
