Morphology of Lonar Crater,India: Comparisons and implications

Lonar Crater is a young meteorite impact crater emplaced in Deccan basalt. Data from 5 drillholes, a gravity network, and field mapping are used to reconstruct its original dimensions, delineate the nature of the pre-impact target rocks, and interpret the emplacement mode of the ejecta. Our estimates of the pre-erosion dimensions are: average diameter of 1710 m; average rim height of 40 m (30–35 m of rim rock uplift, 5–10 m of ejected debris); depth of 230–245 m (from rim crest to crater floor). The crater's circularity index is 0.9 and is unlikely to have been lower in the past. There are minor irregularities in the original crater floor (present sediment-breccia boundary) possibly due to incipient rebound effects. A continuous ejecta blanket extends an average of 1410 m beyond the pre-erosion rim crest.In general, fresh terrestrial craters, less than 10 km in diameter, have smaller depth/diameter and larger rim height/diameter ratios than their lunar counterparts. Both ratios are intermediate for Mercurian craters, suggesting that crater shape is gravity dependent, all else being equal. Lonar demonstrates that all else is not always equal. Its depth/diameter ratio is normal but, because of less rim rock uplift, its rim height/diameter ratio is much smaller than both fresh terrestrial and lunar impact craters. The target rock column at Lonar consists of one or more layers of weathered, soft basalt capped by fresh, dense flows. Plastic deformation and/or compaction of this lower, incompetent material probably absorbed much of the energy normally available in the cratering process for rim rock uplift.A variety of features within the ejecta blanket and the immediately underlying substrate, plus the broad extent of the blanket boundaries, suggest that a fluidized debris surge was the dominant mechanism of ejecta transportation and deposition at Lonar. In these aspects, Lonar should be a good analog for the fluidized craters of Mars.     

Parameters critical to the morphology of fluidization craters

The anomalously high number of craters with diameter less than 2.8 km, the igneous nature of rocks from the Apollo landing sites, and the possibility of outgassing magmas in the lunar crust, suggest that fluidization may be a viable mechanism for producing many of the smaller lunar craters, Fluidization craters were formed in the laboratory by blowing gas through various thicknesses of particulate material. Gas pressure, regolith thickness, and the duration of gas streaming were controlled over practical experimental limits and compared with the resultant crater morphology. Low to moderate fluidization pressures on coarsely crushed limestone (Mø = 0.40, So = =0.50) with low cohesion (ø - 43°) produced bowl shaped, basin shaped, and flat bottomed craters. Bowl shaped craters change into basin shaped and/or flat bottomed craters with long durations of gas streaming. Cone, funnel, and flat-funnel shaped craters are indicative of high fluidization pressures. Craters formed in finely crushed limestone (Mø - 1.55, So - 0.85) that is electrostatically charged by the streaming gas, are flat bottomed. Terraced craters develop from slumping during and after the discontinuation of gas flow. Central mounds inn terraced craters result from slumping into a confined space. In particulate material, fluidization craters have high circularity and axial symmetry, similar to those produced by impact. The use of an impact model and crater morphology (normal, flat bottomed, and concentric) for estimating lunar regolith depth is questioned because similar craters can be produced by fluidizationn processes in a thicker regolith.On leave at the Earth Physics Branch, Dept. of Energy, Mines and Resources, Ottawa, Canada.     

An analysis of the distribution of boulders in the vicinity of small lunar craters

Nine Orbiter 3 high-resolution photographs were examined at three sites for distributions of boulders around craters 110 m in diameter; three kinds of distributions were noted. Some had boulders inside and far outside (designated), others had boulders only inside or on their ramparts (), and some had no detectable boulders (). Additionally, shapes or morphologies of craters were classified according to their resemblance to one of three Jaffe models (1965); a third classification involved the depth of particulate overlay (Jaffe, 1965). Crater morphologies were classified (A) if they were relatively shallow with sharp, raised rims, (B) if they were rimless and shallow, and (C) if they were relatively deep and had low, broad rims. The data suggested that there were strong relationships between crater types and boulder distributions in which, generally, A-type was related to the-distribution, B-type to-distribution, and C-type to-distribution. Plots of numbers of craters of each crater type and each kind of boulder distribution versus steps of overlay for each site and for the totality of craters considered indicated that neither boulder distribution nor crater type represented orderly progression of age or erosional evolution. The apparent overlays for the A's and C's and for the's and's were similar, implying similar ages or stages of erosion. It is suggested that they represent two kinds of primary craters and that the A's are of impact origin while the C's are of volcanic origin. The B's probably represent later stages of erosion of the C's and possibly of some A's.Now at the University of Maryland.Receipt delayed by postal strike in Great Britain.     

Moon: ‘ghost’ craters formed during mare filling

This paper discusses formation of pathological cases of crater morphology due to interaction of craters with molten lavas. Terrestrial observations of such a process are discussed. In lunar maria, a number of small impact craters (D < 10 km) may have been covered by thin layers of fluid lavas, or formed in molten lava. Some specific lunar examples are discussed, including unusual shallow rings resembling experimental craters deformed by isostatic filling.Paper dedicated to Professor Harold C. Urey on the occasion of his 80th birthday on 29 April 1973.     

On the stability of small quasiperiodic motions in the hamiltonian systems

Orbital stability of quasiperiodic motions in the many dimensional autonomic hamiltonian systems is considered. Studied motions are supposed to be not far from equilibrium, the number of their basic frequencies may be not equal to the number of degrees of freedom, and the procedure of their construction is supposed to be converged. The stability problem is solved in the strict nonlinear mode.Obtained results are used in the stability investigation of small plane motions near the lagrangian solutions of the three-dimensional circular restricted three-body problem. The values of parameters for which the plane motions are unstable have been found.

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Sur les solutions Lagrangiennes et euleriennes du probleme generalise des trois corps en axes absolus

Résumé Le présent travail est une continuation d'un autre, publié plus tôt (Doubochine, 1970). On montre ici, que les propriétés des mouvements Lagrangiens et Euleriens établies en mécanique céleste classique sont vraies aussi dans les cas plus généraux, envisagés dans le travail indiqué. On montre de plus, que les trajectoires des points en ces mouvements en axes absolus sont les spirales infinies s'enroulant sur les surfaces des cylindres curvilignes infinis.

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Поле излучения в полубесконечной атмосфере, содержащей источники энергии

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Некоторые асимптотические решения в ограниченной задаче трех тел

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Some asymptotic solutions in the restricted problem of three bodies by L. G. Lukjanov.

Some particular solutions of the plane restricted problem of three bodies in the form of Liapunov's series are obtained. These solutions asymptotically approach the Lagrange solutions. Convergence is proved.

     

Оπорная селенодезическая система координат по гелиометрическим наБлюдениям луны В казани

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Оптимальное демпфирование нутационного движения спутников, стаБилизируемых вращением

, . , , . , , -, This article investigates the dynamics of a system for damping the nutating motion of a spin-stabilized satellite. The equations of motion of the satellite-damper system are derived omitting consideration of the influence of external torques. The conditions of stability of the stationary spinning are obtained and the optimal parameters of the satellite and the damper ensuring a maximal rate of damping of the nutation motion are determined.     

Околозвездньiе облака поданньiм ультрафиолетовьiх спектров свезл

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О влиянии флукаций электронной концентрации на меру дисперсии и мету вращения

, (DM) (RM). , DM RM N _e = n _e ds. M _e = n _e H cos ds ; . Lerche (1970a, b) , DM RM N _e M _e . .     

Le développement du potentiel dans le cas d'une densité analytique

The potential of a body of revolution is expanded in a series of spherical functions. It is proved that, for a body with analytical density limited by an analytical surface the coefficients of expansion decrease in geometrical progression.

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Индуцированное комптоновское рассеяние изотропного излучения релятивистскими электронами

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Повевхное магнитосферное течение С силяными разрывами

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Нитационные демпферы спутников, стаБилиэируемых вгащением

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The stability of the stationary motions of a spin-stabilized satellite is investigated using the Lyapunov second method. The nutating motion of the satellite is damped by a special-purpose device. In case the damping device consists of several independent dampers with one degree of freedom little affecting the satellite motion, their optimal parameters ensuring a maximal rate of damping the nutating motion of the satellite are determined with the hypothesis of resonance adjustmentsof the dampers. The Krylov-Bogolyubov method is used to investigate the influence of external moments on the motion of the satellite rotation axis.

     

St. Magnus Bay,Shetland: A probable British meteorite crater of large size

The last two decades have witnessed a continually expanding programme of investigation concerned with the discovery of terrestrial impact craters or astroblemes as Dietz has called them. These are the wounds produced on the Earth's surface by the high speed collisions with giant meteorites which have taken place throughout geological time. With the exception of a few comparatively recent craters, most of the large scars originated tens or hundreds of millions of years ago and have been preserved as fossils in rocks which have since undergone considerable erosion and alteration.Although various workers have now gathered an impressive array of evidence appertaining to the topographical, petrological and mineralogical changes wrought by the sudden release of enormous quantities of energy when collisions occur, it still remains true that most discoveries of craters are made as a result of their quasi-circular appearance on maps or aerial photographs.A search of maps of the British Isles has revealed several possible impact sites, of which the most convincing is the feature known as St. Magnus Bay in the Shetland Islands. No explanation other than massive impact seems able to account for the peculiar shape of the bay and its resemblance to certain ancient Canadian impact crater residuals.In size it ranks among the dozen or so largest terrestrial impact features and is thus an important object for further study; in its own right and in the context of the currently enhanced speculation concerning the origin of craters on such bodies as the Moon and Mars.     

A model of interplanetary and coronal magnetic fields

A model of the large-scale magnetic field structure above the photosphere uses a Green's function solution to Maxwell's equations. Sources for the magnetic field are related to the observed photospheric field and to the field computed at a source surface about 0.6 R above the photosphere. The large-scale interplanetary magnetic field sector pattern is related to the field pattern at this source surface. The model generates magnetic field patterns on the source surface that compare well with interplanetary observations. Comparisons are shown with observations of the interplanetary magnetic field obtained by the IMP-3 satellite.     

Спэктр тэплового излучения сверхмассивных звезд и рентгеновских источников

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In the external layers of supermassive stars and thermal sources of X-ray radiation electron scattering contributes more to the opacity than free-free processes. Therefore, the thermal radiation spectrum of supermassive stars must greatly differ from Planckian, The approximate formulae obtained for the radiation spectra are applicable to any objects with a predominant role of electron scattering in the opacity and power dependence of plasma temperature and density on geometrical depth of the layers.In thermal radiation sources with power dependence of plasma temperature on depth of the layer the formation of power radiation spectraF(v)v ^– with >0 with >0 is possible. Such spectra can imitate the presence of non-thermal radiation mechanisms. This effect takes place also in the case of small optical depth on the Thomson scattering. Possibly, this effect is of interest for the theories of X-ray sources and X-ray solar flares.

     

Influence du champ magnétique terrestre sur le mouvement d'un satellite autour de son centre de gravité

Résumé On étudie l'effet du champ magnétique terrestre sur le mouvement d'un satellite autour de son centre de gravité. Le satellite possède une symétrie dynamique et un moment magnétique propre dirigé suivant l'un des axes principaux d'inertie; le champ magnétique terrestre est assimilé au champ d'un dipôle dont les pôles coïncident avec les pôles terrestres. On néglige les perturbations de la trajectoire du satellite qui est supposée circulaire. La position du satellite par rapport à son centre de gravité est repérée dans un système d'axes lié au plan de l'orbite et le mouvement est décrit à l'aide des angles d'Euler , , . La symétrie sphérique et le choix du moment magnétique sur l'un des axes d'inertie permettent d'éliminer l'angle .La solution pour et peut se développer en séries de puissance d'un petit paramètre . Les séries convergent pour ||<1.Lorsque le moment magnétique est faible on la rotation du satellite rapide, est faible. Les développements sont calculés effectivement jusqu'à ².La comparaison des résultats avec l'intégration numérique du système d'équations différentielles est satisfaisante.

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The effect of the Earth's magnetic field on the motion of a satellite around its centre of mass is investigated. The satellite is assumed to be dynamically symmetric and to be magnetized in the same direction as that of a principal axis. The Earth's magnetic field is assumed to be a dipole field whose poles coincide with the rotation poles of the Earth. The satellite's orbit is circular and perturbations are neglected. The position of the satellite with respect to its centre of mass is given with respect to a coordinate system fixed in the orbital plane and the motion is described by Euler's angles , , . The spherical symmetry and the coincidence of the magnetic moment with a principal axis allow one to eliminate the angle .The solution for and , can be expanded in power series for small parameter .The series converge for <1. is small for a small magnetic moment or a high angular velocity of the rotating satellite. The terms of the expansion of the series are calculated up to ².The comparison of the results with those obtained by numerical integration of the differential equation is satisfactory.