Mare Imbrium Research Articles

Polarized Magnetic Field Fluctuations at the Apollo 15 Site: Possible Regional Influence on Lunar Induction

High-frequency (5 to 40 millihertz) induced lunar magnetic fields, observed at the Apollo 15 site near the southeastern boundary of Mare Imbrium and the southwestern boundary of Mare Serenitatis, show a strong tendency toward linear polarization in a direction radial to the Imbrium basin and circumferential to the Serenitatis basin, a property that could be indicative of a possible regional influence on the induction.

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.

Gas-Retention and Cosmic-Ray Exposure Ages of Lunar Rock 15555

The last lava flow in the Hadley Rille area of Mare Imbrium, as inferred from an argon-40-argon-39 experiment on a plagioclase separate from the lunar basalt 15555, occurred 3.31+/-0.03x10(9) years ago. An argon-40-argon-39 experiment on a whole rock sample shows significant loss of radiogenic argon-40 and yields a well-defined, high-temperature plateau indicating a lower age of 3.22+/-0.03x10(9) years. A cosmic-ray exposure age of 90+/-10x10(6) years is determined from the ratio of spallogenic argon-38 to calcium.

Lunar Mare Ridges, Rings and Volcanic Ring Complexes

Mare ridges often consist of two separate but related features: (1) a broad gentle arch overlain by (2) a sharper, more contorted ridge. Often these sharper, secondary ridges have flowed into craters in the adjacent terrain indicating they are extrusions. Major flows in Mare Imbrium appear to have issued from several prominent mare ridges. These flows show color differences which may be related to their abundance of titanium. The association of flows with mare ridges, the broad arching linked with many ridges and the coincidence of linear ridges with the directions of major fracture patterns in the highlands indicates that arched mare ridges are dike, sill or laccolithic-type intrusions along major fractures. In many cases these intrusions appear to have broken through the surface to form short flows and bulbous lava extrusions. Mare ridges unassociated with arching are probably lava extrusions only.Mare ridges often take the form of rings indicating that they developed along ring fractures. Several linear mare ridges and mare ridge rings have bright hills situated along them and are considered to be post-mare volcanic hills of more siliceous composition than the maria. Evidence suggests that many of the ring structures are post-mare volcanic ring complexes formed over large igneous masses.

Gas retention and cosmic-ray exposure ages of a basalt fragment from Mare Fecunditatis

An 40Ar- 39Ar gas retention age and an 38Ar- 37Ar cosmic ray exposure age have been determined on a total rock sample of the basalt fragment B-1 returned from Mare Fecunditatis by the Luna 16 mission. This sample shows large low-temperature loss of radiogenic 40Ar but defines a reasonably good high-temperature plateau at 3.45 ± 0.04 AE. This is presumed to date a period of igneous activity in Mare Fecunditatis. This activity is later than that at Mare Tranquillitatis but earlier than at Oceanus Procellarum and Mare Imbrium. The cosmic ray exposure age is 475 m.y.

Geologic Setting of the Apollo 14 Samples

The Apollo 14 lunar module landed in a region of the lunar highlands that is part of a widespread blanket of ejecta surrounding the mare Imbrium basin. Samples were collected from the regolith developed on a nearly level plain, a ridge 100 meters high, and a blocky ejecta deposit around a young crater. Large boulders in the vicinity of the landing site are coherent fragmental rocks as are some of the returned samples.

Lunar Radar Mapping: Correlation between Radar Reflectivity and Stratigraphy in North-western Mare Imbrium

DELAY-DOPPLER radar maps of the Moon obtained with the 430 MHz (70 cm wavelength) radar of the Arecibo Ionospheric Observatory in Puerto Rico (Thompson, unpublished) are at present being studied to correlate geological information with the radar reflexion characteristics of the lunar surface. Preliminary evaluation of the radar data for the Sinus Iridum quadrangle (32°–48° N; 14°–38° W) has revealed that the lowest values of radar reflectivity are closely correlated with the mare materials of lowest albedo mapped by Schaber1 as of most recent volcanic origin. These radar data were obtained with a surface resolution of 50 to 100 km2 on January 24 and April 17, 1967. A detailed account of the delay-doppler radar mapping technique can be found in unpublished reports by Thompson.

Doppler gravity, A new method

The method recently applied by P. M. Muller and W. L. Sjogren in mapping gravity anomalies of the moon employed a new principle of gravity measurement: time differentiation of Doppler-tracked velocities. Utilization of this method offers a promising new area of planetary investigation yielding data that, up to present, would have required landed mobile instrumentation. Analysis of the method shows that, unlike conventional terrestrial gravity, Doppler gravity varies in direction, depending on the configuration of the Doppler system; other configurations are possible which may yield data of improved analytical quality. A comparison of the Mare Imbrium Doppler gravity anomaly with theoretical curves indicates that the source is plate-like in shape. Topographic effects, however, must be evaluated before a complete analysis is possible. Comparison of anomalies and topography indicates that lunar surface features are not in isostatic equilibrium. Minor modifications of the present system that should yield data of improved analytical quality include more circular orbits and lower altitudes.

Radiometric Measurements of the Moon at 8.6- and 3.2-MILLIMETER Wave-Lengths

view Abstract Citations (6) References (6) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radiometric Measurements of the Moon at 8.6- and 3.2-MILLIMETER Wave-Lengths Clardy, D. E. ; Straiton, A. W. Abstract Lunar thermal-radiation data were recorded at wavelengths of 8.6 and 3.2 mm with a 16-foot-diame- ter antenna system at Austin, Texas. The data provided contours of equal brightness temperatures over the lunar disk at intervals of approximately 24° in lunar phase angle. Variations of brightness tempera- ture with time are presented in curves and as Fourier components for the selenographic center, the area around Surveyor I, Mare Tranquillitatis, Mare Imbrium, Copernicus, and the highland area around 100 W., 200 S. Comparison is made with similar measurements made with antenna beams 12' or less Publication: The Astrophysical Journal Pub Date: November 1968 DOI: 10.1086/149797 Bibcode: 1968ApJ...154..775C full text sources ADS |

VI. The nature of the Moon’s surface - The lunar surface and the U. S. Ranger programme

The unaided eye can see roundish dark spots on the Moon set in a brighter back­ground. Telescopic observation of these dark spots, called maria (plural of mare , sea) reveals that they are nearly level terrain sparsely covered with craters. The brighter surroundings or terrae are from shadow measurements found to be higher, some 1 to 3 km above the maria. The terra elevations scatter widely, reaching several kilometres in the mountain ranges. The most prominent of these ranges occur as peripheral mountain chains around the near-circular maria. Examples are the Apennines, the Alps, the Carpathians, and the Altai Scarp. These arcuate chains surround the maria as the crater walls surround crater floors, an analogy that can be carried further and implies, apart from scale, a similar origin. This origin is almost certainly impact by massive objects. In the case of the impact maria and pre-mare craters, the source of the objects appear to have been a satellite ring around the Earth through which the Moon swept very early in its history, in its outward journey from its position of origin very near the Earth (Kuiper 1954, 1965). The post-mare craters are presumably mostly asteroidal (and partly comet­ary) in origin and related to the craters observed by Mariner IV on Mars. The estimated time dependencies of these two crater-forming processes are shown schematically in figure 1. A fuller discussion of this problem has been given else­where (Kuiper, Strom & Poole 1966; Kuiper 1966). The higher asteroidal impact rate on Mars, by a factor of about 15, as derived from the Mariner IV records, is interpreted as being due to the greater proximity to the asteroid ring. The num­erical factor approximately agrees with theory. Mars apparently lacks the equiva­lent of the initial excessively intense bombardment of the Moon (attributed to impacts by circumterrestrial bodies); unless, of course, the entire Martian surface has been molten and is directly comparable to the lunar maria. This does not seem probable but can at present not be ruled out; if true, the earliest surface history would have been erased. The nature of the mare surface has, during the past decade, been an object of much, perhaps too much, speculation. With the several recent successful lunar reconnaissance missions completed, the older interpretation of the maria as lava beds, based on telescopic observation, has been abundantly confirmed. Four options discussed in recent literature are analysed in Kuiper (1965, §§A, B, pp. 12–39). Among the most potent arguments for the lava cover of the maria are the prominent lava flows observed on Mare Imbrium and Mare Serenitatis, each having a characteristic colour. A map of some Mare Imbrium flows is found in figure 2.

Results of a Radiometric Moon-Mapping Investigation at 3 Millimeters Wavelength

view Abstract Citations (8) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Results of a Radiometric Moon-Mapping Investigation at 3 Millimeters Wavelength Gary, B. Abstract This is the second of two papers describing an attempt to determine the nature of the lunar surface material from an analysis of the monthly variation of the Moon's 3.3-mm wavelength thermal emission. The Aerospace Corporation 15-foot-diameter radio telescope was used to construct high angular resolution radiometric maps consisting of brightness temperature contours on the Moon's disk for 14 representative lunar phases An analysis has been performed on the thermal behavior of five maria and portions of a large highland region. The final results of this analysis are reported in the present paper. The observed temperature variation during a lunation has been compared with predictions based on a model for the lunar surface which allows for the existence of vertical and horizontal inhomogeneities of certain parameters of the lunar material. Values for these parameters have been subjected to constraints imposed by infrared observations of the lunar nighttime surface temperature. No combination of parameter values permitted by these constraints can account for the microwave observations. Suggestions for possible improvements of the lunar model are given. Comparisons of the thermal behavior of different locations on the Moon reveal that the lunationaveraged temperature of the five maria investigated exceeds that of the highlands by 2.60 * 0.20 K, whereas albedo considerations lead to an expected temperature excess of only 0.80 i 030 K. An attempt is made to explain this discrepancy by associating the mare surfaces with either a greater abundance of rock (exposed, or close to the surface) or a smaller value for the lunar material's thermal inertia reciprocal, . The mare-highland temperature excess varies during a lunation between 0 K and +60 K for Mare Nubium, Mare Imbrium, and the mare region near Copernicus. Mare Serenitatis exhibits a 90 K variation, and the temperature excess of Mare Tranquilitatis appears to remain constant. An unsuccessful attempt to explain these variations provides further demonstration of the need for a more sophisticated model for the lunar surface. Publication: The Astrophysical Journal Pub Date: January 1967 DOI: 10.1086/148996 Bibcode: 1967ApJ...147..245G full text sources ADS |

3.2-mm Observations of the Lunar Eclipse of 30 December 1963

view Abstract Citations (2) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS 3.2-mm Observations of the Lunar Eclipse of 30 December 1963 Epstein, Eugene E. ; Stacey, Joseph M. Abstract Previous radio astronomical observations, at X>3.2 mm, during lunar eclipses have not reliably detected any temperature changes. However, no observations have been made at X~3.2 mm. A 15-ft, 3-min of arc beamwidth antenna, operating at X=3.2 mm, was used from 05h UT to 14h UT, 30 December 1963, to observe the subterrestrial point, a mountainous region near Sinus Medii, Mare Serenitatis, Mare Imbrium, and Copernicus. The temperatures of all five regions decreased 6% during the eclipse. The data show no statistically significant differences in the maximum temperature decreases or in the rates of cooling and recovery of the five regions. Cooling and recovery of each region commenced within ~1li of the entry into and exit from, respectively, the umbra. This research has been supported by U. S. Air Force Contract No. AF 04(695)-269. Publication: The Astronomical Journal Pub Date: 1964 DOI: 10.1086/109393 Bibcode: 1964AJ.....69Q.541E full text sources ADS |

Lunar tectonics

The lunar lineaments are described and their origin is considered. The components of the lunar grid-system—a system of intersecting lineaments comprised of elongated ridges, joints, crater-chains, and rilles—are described, and methods for producing orthographic charts of the principal global families A, B, C, and D of the grid-system are given. Each family, or system, of lineaments has a well-defined strike and is distinguished from one major regional system of joints (system R 1 ) which is associated with Mare Imbrium The global systems display a strong symmetry about the Moon’s central meridian. Discussion of the origin of system R 1 and a similar regional system of joints associated with Mare Humorum leads to the conclusion that these maria are igneous sinks and were not produced by impact. Examples of dip-slip and strike-slip faults are given. General properties of the mutally orthogonal systems A and B are listed and interpreted in terms of a general meridional pressure in the Moon’s crust.

Origin of the Mare Imbrium

G. K. GILBERT1 proposed that a large-scale collision occurred in Mare Imbrium and this hypothesis has been supported by R. B. Baldwin2 and, ardently, by H. C. Urey3. Other authors, however, have preferred to explain the radial symmetry without resort to dualism. Thus, Tomkins4, Spurr5, Kuiper6 and von Bulow7 considered that parts of the radial system were produced by faulting.

Comparison of the Ocean Floor with the Lunar Surface

Many attempts have been made to compare the smaller features of the moon with earthly features. Thus such familiar structural items as lava flows, faults, domes, and pressure ridges have been delineated. The larger lunar features—the maria, the mountains, the clefts, and the larger craters—have not heretofore been thought to have earthly counterparts. There are two principal theories of origin of the lunar features—volcanic and meteoritic. Both theories lead to the conclusion that the agent which produced the structures was more active in the past and may have been essentially dormant since the Archeozoic era. The most likely place on earth to search for similar features is in areas that have remained little changed since that time. In many ways the floor of the Atlantic Ocean resembles the moon9s surface. The Madeira Abyssal Plain is similar in size and shape to Mare Crisium; the Sohm Abyssal Plain is very like Oceanus Procellarum or Mare Frigoris; the Mid-ocean ridge is reminiscent of the lunar uplands; mid-ocean canyons recall the clefts of the moon; and the sea-mounts are like the isolated peaks and mountains of the Mare Imbrium district. East of Bermuda is a range of low hills (abyssal hills) arranged in a fan-shape very similar to the lunar Haemus Mountains. Two gashes across the Mid-Atlantic ridge, one at Lat. 30°N. and one at the equator, are very like the Alpine Valley of the moon. Steep slopes are characteristic of both the lunar mountains and the submarine slopes of the Atlantic. Both the Atlantic floor and the topographically low areas of the moon are thought to be blanketed with dust-sized material.

DATING LUNAR SURFACE FEATURES BY USING CRATER FREQUENCIES

Several theories have been advanced relating to the modes of formation and the ages of lunar surface features. Baldwin has proposed that the maria were formed so early in lunar history that only a small fraction of the Archeozoic age had passed.1 According to Kuiper, Mare Imbrium resulted from a major impact occurring nearly a billion years after the formation of the moon,2 while Urey believes that the bombardment causing Mare Imbrium occurred between 3 and 4. 5 billion years ago,3 and Gold attributes the present surface of Mare Imbrium to eroded materials that have accumulated over the entire lunar history.4 The ages of certain lunar features have recently been estimated by Lyubarski, who computed the number of meteoritic bodies falling on the moon per year per square km under certain assumptions concerning the velocity and mass distributions of the meteorites.5 In his investigation, Lyubarski found an age for Mare Tranquilitatis of between 2 and 46 million years and an age for Mare Humorum of between 4 and 94 million years. These estimates correspond to upper Cretaceous and early Tertiary periods. We have followed a somewhat different method by which large craters and maria are dated by comparing the number of craters of a given diameter per square km in these areas with the corresponding number of craters in the continental areas. We have also assumed a constant and isotropie meteoric influx on the moon.

The Lunar Surface as an Impact Counter

The dust cover of the Moon sticks to mountain slopes and cannot possess any degree of fluidity. It is probable that only a limited migration of the dust from the slopes into adjacent valleys takes place, caused by meteor bombardment. The material of the micrometeors cannot escape from the Moon and is expected to form a layer of the order of 40 gr/cm 2 , accumulating over the maria and protecting them from further erosion by small meteors. Large meteorites are not stopped by the dust and produce meteor craters; at a velocity of 20 km/sec the ratio of crater to projectile diameter is estimated to be about 20. 812 crater diameters, measured over an area of 465,000 km 2 in Western Mare Imbrium, show a frequency distribution which is close to that predicted from the present population of interplanetary space and a time interval of 4.5 × 10 9 years. It is concluded that since the formation of Mare Imbrium the population of interplanetary space has not changed appreciably; a tentative explanation is given.

Appendix: A report on recent lunar studies and their bearing on the nature of terrestrial continents and ocean basins

The common distinction between the low dark maria and high brighter continents, readily made on lunar photographs, must be refined. The bright areas are of two types: (1) accreted crust, modified by a sequence of impacts that led to the formation of the familiar large lunar craters; and (2) maria or accreted crust, buried by material clearly ejected from Mare Imbrium and a few smaller splash centers. The major mountain ranges (Alps, Caucasus, Apennines, Carpathians) belong in this second category; they seem to be composed of light‐colored blocks of crust, mixed with large quantities of darker lava, now solidified, which look somewhat like mud flows.The recent suggestion by T. Gold and others that the maria are featureless because they are Med with a very deep layer of dust is contradicted by several groups of observations: (1) The maria, seen under very low Sun, show an intricate fine structure, including discrete flows, minor faults, graben, etc. (2) Impact craters situated on the ‘shore’ lines of maria are often tipped toward the mare, like partly‐sunk boats lying against the shore line of a lake. Apparently, the foundations of these crater mins were melted locally and the ruins have subsided or even submerged. (3) A compelling argument is derived in the next paragraph from the nature of the ridges on the maria. (4) There is no trace of a filling effect of very small craters such as a thick, mobile dust layer would cause. Actually, the maria are beset with hundred of small craters iabout 1 km in diameter and smaller), whose numbers and shapes indicate that they are meteoritic in origin. Large craters, (10 to 100 km), as found on the continents, are nearly absent on the maria. These large craters appear to represent an early phase of lunar development, preceding the development of the maria and partly concurrent with it. The maria were probably formed about 4.5 billion years ago.

THE EXPLOSION CRATERS OF THE MOON

tated the subsidences that gave us the maria and the walled plains, but, with the possible exception of the central part of Mare Imbrium, they did little more. The adjective typical is used because some features which have been referred to as mountain walled differ from the true ones and should have been designated as ringed plains. Arzachel is an excellent example of such an error. It appears to show effects both of major explosion and of subsidence. The walled plains have little or no external walls. Ringed plains have definite ones and primarily are explosive in nature. They are the largest of the explosion craters. For the purposes of this study, any crater that has resulted from any sort of internal force will be spoken of as volcanic, even though some possible impact may have been an indirect cause, as in the cases of the craterlets near Copernicus and Tycho. Most of the data used in this study are shown on the photographic plates

Die Entstehung des Mare Imbrium und der Mondrillen

Die Entstehung des Mare Imbrium und der Mondrillen