The apollo 15 lunar samples: a preliminary description

Samples returned from the Apollo 15 site consist of mare basalts and breccias with a variety of premare igneous rocks. The mare basalts are from at least two different lava flows. The bulk chemical compositions and textures of these rocks confirm the previous conclusion that the lunar maria consist of a series of extrusive volcanic rocks that are rich in iron and poor in sodium. The breccias contain abundant clasts of anorthositic fragments along with clasts of basaltic rocks much richer in plagioclase than the mare basalts. These two rock types also occur as common components in soil samples from this site. The rocks and soils from both the front and mare region exhibit a variety of shock characteristics that can best be ascribed to ray material from the craters Aristillus or Autolycus.     

Petrogenesis of lunar basalts and the internal constitution and origin of the moon

Petrographic and electron-microprobe studies combined with high pressure-temperature investigations of phase relationships in average Apollo 11 basalt and possible source material show that the lower parts of maria may be composed of eclogite (density 3.74 grams per cubic centimeter), thus explaining the existence of mascons. The Apollo 11 basalt was probably formed at depths of 200 to 400 kilometers by a small degree of partial melting from pyroxenitic source material [FeO/(FeO + MgO) = 0.25, A1(2)O(3) 4 percent, CaO 3 percent]. This composition may be representative of the lunar interior and yields the observed mean lunar density and moment of inertia. Present data are in conflict with fission, binary planet, and capture hypotheses of lunar origin but are consistent with Ringwood's (1966) precipitation hypothesis.     

Lunar Orbiter Photographs: Some Fundamental Observations: Preliminary study reveals details of craters, crater distributions, and the major types of terrain

High-resolution photographs returned by Orbiters II and III typically show a surface pitted with small, perfectly circular craters as much as 50 meters in diameter, some of which are strongly clustered; these are superposed on larger, generally shallower craters and must be a mixture of primary and secondary impact craters. Rough terrain is less heavily cratered but is crossed by numerous closely spaced troughs and ridges up to 3 meters high. Terraces, which commonly occur at the base of steep slopes, are also crossed by these troughs and ridges and have relatively few craters. Fresh craters-craters whose exterior slopes are covered with material different from that of the intercrater areas-are rare and are surrounded by angular blocks up to 80 meters in diameter, in varying numbers; these craters apparently undergo gradual destruction to shallow gentle depressions. The frequency of craters 100 meters and more in diameter varies widely, even on level terrain; some of the highest concentrations of craters occur on rays.     

Lunar Gravity over Large Craters from Apollo 12 Tracking Data

The Doppler residuals from the Apollo 12 lunar module radio tracking data indicate large negative accelerations over the craters Ptolemaeus and Albategnius. The mass deficienicies required to produce these accelerations are approximately equivalent to the removal of the surface material to a depth of 1 kilometer over the entire area of these craters. Several other features of the gravity fine structure can also be correlated with topography.     

Lunar surface radioactivity: preliminary results of the apollo 15 and apollo 16 gamma-ray spectrometer experiments

Gamma-ray spectrometers on the Apollo 15 and Apollo 16 missions have been used to map the moon's radioactivity over 20 percent of its surface. The highest levels of natural radioactivity are found in Mare Imbrium and Oceanus Procellarum with contrastingly lower enhancements in the eastern maria. The ratio of potassium to uranium is higher on the far side than on the near side, although it is everywhere lower than commonly found on the earth.     

The moon: sources of the crustal magnetic anomalies

Previously unmapped Apollo 16 subsatellite magnetometer data collected at low altitudes over the lunar near side are presented. Medium-amplitude magnetic anomalies exist over the Fra Mauro and Cayley Formations (primary and secondary basin ejecta emplaced 3.8 to 4.0 billion years ago) but are nearly absent over the maria and over the craters Copernicus, Kepler, and Reiner and their encircling ejecta mantles. The largest observed anomaly (radial component approximately 21 gammas at an altitude of 20 kilometers) is exactly correlated with a conspicuous light-colored deposit on western Oceanus Procellarum known as Reiner gamma. Assuming that the Reiner gamma deposit is the source body and estimating its maximum average thickness as 10 meters, a minimum mean magnetization level of 5.2 +/- 2.4 x 10(-2) electromagnetic units per gram, or approximately 500 times the stable magnetization component of the most magnetic returned sample, is calculated. An age for its emplacement of 相似文献   

Lunar maria: structure and evolution

The lunar maria are considered to have evolved as homologous, transient, gravity-wave systems from large impact craters on a crustal layer 50 kilometers thick, fluidized from beneath by prompt, shock-induced melting inside an initially hot moon.     

Apollo 15 Geochemical X-ray Fluorescence Experiment: Preliminary Report

Although only part of the information from the x-ray fluorescence geochemical experiment has been analyzed, it is clear that the experiment was highly successful. Significant compositional differences among and possibly within the maria and highlands have been detected. When viewed in the light of analyzed lunar rocks and soil samples, and the data from other lunar orbital experiments (in particular, the Apollo 15 gamma-ray spectroscopy experiment), the results indicate the existence of a differential lunar highland crust, probably feldspathic. This crust appears to be related to the plagioclase-rich materials previously found in the samples from Apollo 11, Apollo 12, Apollo 14, Apollo 15, and Luna 16.     

Radar glory from buried craters on icy moons

Three ice-covered moons of Jupiter, in comparison with rocky planets and Earth's moon, produce radar echoes of astounding strengths and bizarre polarizations. Scattering from buried craters can explain these and other anomalous properties of the echoes. The role of such craters is analogous to that of the water droplets that create the apparition known as "the glory," the optically bright region surrounding an observer's shadow on a cloud. Both situations involve the electromagnetic phenomenon of total internal reflection at a dielectric interface, operating in a geometry that strongly favors exact backscattering. Dim surface craters are transformed into bright glory holes by being buried under somewhat denser material, thereby increasing the intensity of their echoes by factors of hundreds. The dielectric interface thus formed at the crater walls nicely accounts for the unusual polarizations of the echoes.     

The impact cratering record on triton

Impact craters on Triton are scarce owing to the relatively recent resurfacing by icy melts. The most heavily cratered surface has a crater density about the same as the lunar maria. The transition diameter from simple to complex craters occurs at a diameter of about 11 kilometers, and the depth-diameter relationship is similar to that of other icy satellites when gravity is taken into account. The crater size-frequency distribution has a differential -3 slope (cumulative -2 slope) and is the same as that for the fresh crater population on Miranda. The most heavily cratered region is on the leading hemisphere in Triton's orbit. Triton may have a leading-trailing asymmetry in its crater population. Based primarily on the similarity of size distributions on Triton and Miranda and the relatively young surface on Triton, the source of Triton's craters is probably comets. The very peculiar size distribution of sharp craters on the "cantaloupe" terrain and other evidence suggests they are volcanic explosion craters.     

The martian surface

With the scarcity of factual data and the difficulty of applying crucial tests, many of the properties of the Martian surface remain a mystery; the planet may become a source of great surprises in the future. In the following, the conclusions are enumerated more or less in the order of their reliability, the more certain ones first, conjectures or ambiguous interpretations coming last. Even if they prove to be wrong, they may serve as a stimulus for further investigation. Impact craters on Mars, from collisions with nearby asteroids and other stray bodies, were predicted 16 years ago (5-7) and are now verified by the Mariner IV pictures. The kink in the frequency curve of Martian crater diameters indicates that those larger than 20 kilometers could have survived aeolian erosion since the "beginning." They indicate an erosion rate 30 times slower than that in terrestrial deserts and 70 times faster than micrometeorite erosion on the moon. The observed number, per unit area, of Martian craters larger than 20 kilometers exceeds 4 times that calculated from the statistical theory of interplanetary collisions with the present population of stray bodies and for a time interval of 4500 million years, even when allowance is made for the depletion of the Martian group of asteroids, which were more numerous in the past. This, and the low eroded rims of the Martian craters suggest that many of the craters have survived almost since the formation of the crust. Therefore, Mars could not have possessed a dense atmosphere for any length of time. If there was abundant water for the first 100 million years or so, before it escaped it could have occurred only in the solid state as ice and snow, with but traces of vapor in the atmosphere, on account of the low temperature caused by the high reflectivity of clouds and snow. For Martian life there is thus the dilemma: with water, it is too cold; without, too dry. The crater density on Mars, though twice that in lunar maria, is much smaller than the "saturation density" of lunar highlands. Many primeval craters, those from the last impacts which formed the planet, must have become erased, either by late impacts of preferentially surviving large asteroids or by a primeval atmosphere which rapidly escaped. The tenuous Martian atmosphere may have originated entirely from outgassing of surface rocks by asteroidal impacts, which also could have produced some molten lava. The role of genuine volcanism on Mars must have been insignificant, if any. The large amplitude in temperature indicates that the Martian upper soil, equally in the bright and the dark areas, is of a porous unconsolidated structure, with a thermal conductivity as low as that of atmospheric air. Limb darkening at full phase in green, yellow, and red light indicates absorption by atmospheric haze, aerosols, and dust. The loss of contrast in the blue and violet is caused by stronger absorptivity of the haze, which is almost as dark as soot, and not by a true decrease in contrast of the surface markings. Photometric measurementsin the blue reveal a residual contrast of 5 to 7 percent between the markings in 1958, invisible to the eye at a time when there was no "blue clearing." The surface brightness of the maria was surprisingly uniform in 1958 (late summer in the southern hemisphere), while the continentes showed considerable variation. In view of the spotty microstructure of the Martian surface as revealed by Mariner IV, and the lack of a sharp border between a mare and a continens, it seems that all the difference consists in the relative number of small dark and bright areas in the surface mosaic. If there is vegetation on Mars, it should be concentrated in the darkarea elements, measuring 10 to 100 kilometers. Vegetation is the best hypothesis to account for seasonal changes in the maria and for the persistence of these formations despite dust storms of global extent. Survival of vegetation in the extreme dryness of the Martian climate could depend on the low night-time temperature and deposition of hoarfrost, which could melt into droplets after sunrise, before evaporating. If not vegetation, it must be something thing specifically Martian; no other hypothesis hitherto proposed is able to account for the facts. However, the infrared bands which at one time were thought to be associated with the presence of organic matter, belong to heavy water in the terrestrial atmosphere. The conversion of a former bright area into a dark one in 1954, over some 1 million square kilometers, is the largest recorded change of this kind. Even on the vegetation hypothesis, it eludes satisfactory explanation. Relatively bright areas observed in the blue and violet in polar regions and elsewhere on the limb can be explained by a greater transparency of the atmosphere,its dust content being decreased by a downward (anticyclonic) current. The surface, of a greater reflecting power than the atmospheric smoke, then becomes visible. The sudden explosion-like occurrence of yellow or gray clouds, reducing atmospheric transparency and surface contrast, could be due to impacts of asteroids; in such a case, however, the number of unobservable small asteroids, down to 30 to 40 meters in diameter, should greatly exceed the number extrapolated from the larger members of the group. A "meteoritic" increment in numbers, instead of the asteroidal one, would be required. special observations with large Schmidt telescopes could settle this crucial question. The Martian "oases," centers of "canal" systems, could be impact creters. The canals may be real formations, without sharp borders and 100 to 200 kilometers wide, due to a systematic alignment. of the dark surface elements. They may indicate cracks in the planet's crust, radiating from the point of impact.     

Lonar lake, India: an impact crater in basalt

Discovery of shock-metamorphosed material establishes the impact origin of Lonar Crater. Coarse breccia with shatter coning and microbreccia with moderately shocked fragments containing maskelynite were found in drill holes through the crater floor. Trenches on the rim yield strongly shocked fragments in which plagioclase has melted and vesiculated, and bombs and spherules of homogeneous rock melt. As the only known terrestrial impact crater in basalt, Lonar Crater provides unique opportunities for comparison with lunar craters. In particular, microbreccias and glass spherules from Lonar Crater have close analogs among the Apollo specimens.     

Lunar transient phenomena: topographical distribution

The sites named in nearly 400 reports of lunar transient phenomena fall into three classes: (i) sites peripheral to the maria, (ii) ray craters, and (iii) ring plains with dark or partially dark floors; none are known in the rugged highland area of the southeast (International Astronomical Union, 1964; classically southwest) quadrant. Permanent records are few; the sites where known are consistent with the visual records.     

Apollo 12 lunar module impact: laboratory simulation and possible downrange ballistic effects

Plastic pellets were fired into sand targets at a launch angle of 4 degrees and a velocity of 1.68 kilometers per second, the conditions of the Apollo 12 lunar module impact. Shallow elliptical or doublet craters were formed, similar to certain lunar craters. Analysis of the ejecta suggests (i) that lunar module debris skipped and, with some crater ejecta, reimpacted far downrange, but (ii) this ballistic rain does not account for the anomalous seismic signal.     

History of meteorites from the moon collected in antarctica

In large asteroidal or cometary impacts on the moon, lunar surface material can be ejected with escape velocities. A few of these rocks were captured by Earth and were recently collected on the Antarctic ice. The records of noble gas isotopes and of cosmic ray-produced radionuclides in five of these meteorites reveal that they originated from at least two different impact craters on the moon. The chemical composition indicates that the impact sites were probably far from the Apollo and Luna landing sites. The duration of the moon-Earth transfer for three meteorites, which belong to the same fall event on Earth, lasted 5 to 11 million years, in contrast to a duration of less than 300,000 years for the two other meteorites. From the activities of cosmic ray-produced radionuclides, the date of fall onto the Antarctic ice sheet is calculated as 70,000 to 170,000 years ago.     

Deimos encounter by viking: preliminary imaging results

Recent close flybys of Deimos by Viking revealed a smooth-appearing surface void of grooves. Higher-resolution pictures showed that the surface was actually covered with craters but that a regolith filled the smaller craters, giving the smooth appearance. The surface was also covered with boulders and bright streak-like markings analogous to base-surge or ejecta cloud deposits.     

Preliminary examination of lunar samples from apollo 14

The major findings of the preliminary examination of the lunar samples are as follows: 1) The samples from Fra Mauro base may be contrasted with those from Tranquillity base and the Ocean of Storms in that about half the Apollo 11 samples consist of basaltic rocks, and all but three Apollo 12 rocks are basaltic, whereas in the Apollo 14 samples only two rocks of the 33 rocks over 50 grams have basaltic textures. The samples from Fra Mauro base consist largely of fragmental rocks containing clasts of diverse lithologies and histories. Generally the rocks differ modally from earlier lunar samples in that they contain more plagioclase and contain orthopyroxene. 2) The Apollo 14 samples differ chemically from earlier lunar rocks and from their closest meteorite and terrestrial analogs. The lunar material closest in composition is the KREEP component (potassium, rare earth elements, phosphorus), "norite," "mottled gray fragments" (9) from the soil samples (in particular, sample 12033) from the Apollo 12 site, and the dark portion of rock 12013 (10). The Apollo 14 material is richer in titanium, iron, magnesium, and silicon than the Surveyor 7 material, the only lunar highlands material directly analyzed (11). The rocks also differ from the mare basalts, having much lower contents of iron, titanium, manganese, chromium, and scandium and higher contents of silicon, aluminum, zirconium, potassium, uranium, thorium, barium, rubidium, sodium, niobium, lithium, and lanthanum. The ratios of potassium to uranium are lower than those of terrestrial rocks and similar to those of earlier lunar samples. 3) The chemical composition of the soil closely resembles that of the fragmental rocks and the large basaltic rock (sample 14310) except that some elements (potassium, lanthanum, ytterbium, and barium) may be somewhat depleted in the soil with respect to the average rock composition. 4) Rocks display characteristic surface features of lunar material (impact microcraters, rounding) and shock effects similar to those observed in rocks and soil from the Apollo 11 and Apollo 12 missions. The rocks show no evidence of exposure to water, and their content of metallic iron suggests that they, like the Apollo 11 and Apollo 12 material, were formed and have remained in an environment with low oxygen activity. 5) The concentration of solar windimplanted material in the soil is large, as was the case for Apollo 11 and Apollo 12 soil. However, unlike previous fragmental rocks, Apollo 14 fragmental rocks possess solar wind contents ranging from approximately that of the soil to essentially zero, with most rocks investigated falling toward one extreme of this range. A positive correlation appears to exist between the solar wind components, carbon, and (20)Ne, of fragmental rocks and their friability (Fig. 12). 6) Carbon contents lie within the range of carbon contents for Apollo 11 and Apollo 12 samples. 7) Four fragmental rocks show surface exposure times (10 x 10(6) to 20 x 10(6) years) about an order of magnitude less than typical exposure times of Apollo 11 and Apollo 12 rocks. 8) A much broader range of soil mechanics properties was encountered at the Apollo 14 site than has been observed at the Apollo 11, Apollo 12, and Surveyor landing sites. At different points along the traverses of the Apollo 14 mission, lesser cohesion, coarser grain size, and greater resistance to penetration was found than at the Apollo 11 and Apollo 12 sites. These variations are indicative of a very complex, heterogeneous deposit. The soils are more poorly sorted, but the range of grain size is similar to those of the Apollo 11 and Apollo 12 soils. 9) No evidence of biological material has been found in the samples to date.     

Martian topography: large-scale variations

The variation in carbon dioxide abundances detected in the 1.05-micron band over small, discrete areas on Mars indicates that larger-scale topographical differences are present than had previously been believed. Spectroscopic mapping of the surface also indicates no apparent correlation between albedo and height; the results are in good agreement with topographical data derived from the range-gated rodar scan along +21 degrees N. High and low areas are found in both the major equatorial maria and the bright deserts in the northern hemisphere.     

Geology of the Caloris basin, Mercury: a view from MESSENGER

The Caloris basin, the youngest known large impact basin on Mercury, is revealed in MESSENGER images to be modified by volcanism and deformation in a manner distinct from that of lunar impact basins. The morphology and spatial distribution of basin materials themselves closely match lunar counterparts. Evidence for a volcanic origin of the basin's interior plains includes embayed craters on the basin floor and diffuse deposits surrounding rimless depressions interpreted to be of pyroclastic origin. Unlike lunar maria, the volcanic plains in Caloris are higher in albedo than surrounding basin materials and lack spectral evidence for ferrous iron-bearing silicates. Tectonic landforms, contractional wrinkle ridges and extensional troughs, have distributions and age relations different from their counterparts in and around lunar basins, indicating a different stress history.     

Lunar apennine-hadley region: geological inplications of Earth-based radar and infrared measurements

Recently completed high-resolution radar maps of the moon contain information on the decimeter-scale structure of the surface. When this information is combined with eclipse thermal-enhancement data and with high-resolution Lunar Orbiter photography, the surface morphology is revealed in some detail. A geological history for certain features and subareas can be developed, which provides one possible framework for the interpretation of the findings from the Apollo 15 landing. Frequency of decimeter-and meter-size blocks in and around lunar craters, given by the remote-sensed data, supports a multilayer structure in the Palus Putredinis mare region, as well as a great age for the bordering Apennine Mountains scarp.