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1.
In this paper a theory is evaluated to describe the development of the lunar crater population with time under the bombardment by meteoroids and solar wind. Starting from a general mass distribution law a differential equation has been established and solved separately for meteoroid impact and solar wind bombardment. The theory permits the calculation of absolute formation ages of the lunar surface as well as the particle flux, supposing the crater distributions on the moon have been measured. As an important result it includes a D−2 equilibrium crater distribution law (D =crater diameter), actually measured in Mare Tranquillitatis and Oceanus Procellarum. Additionally, the exponential decrease of particle flux with time is confirmed.  相似文献   

2.
An interpretation of previously reported measurements of the Apollo 15/16 alpha-particle spectrometer on the distribution of 222Rn and 210Po across the lunar surface suggests that continuation of these measurements is a method of monitoring current activity on the moon. Since the two isotopes are relatively short-lived with effective half-lives of 3 days and 21 years, respectively, the activity detected has had to have been released during this current epoch. Changes in the rate of lunar emanation can be measured on three different time scales: (1) of a few days or less by detecting 222Rn at discrete sites such as the crater Aristarchus; (2) of a month by measuring 222Rn activity at the sunrise terminator; (3) of a few years by measuring 210Po activity at various locations. These observations could be carried out very effectively from a lunar polar orbiting satellite.  相似文献   

3.
A summary of experiments and analyses concerning electromagnetic induction in the Moon and other extraterrestrial bodies is presented. Magnetic step-transient measurements made on the lunar dark side show the eddy current response to be the dominant induction mode of the Moon. Analysis of the poloidal field decay of the eddy currents has yielded a range of monotonic conductivity profiles for the lunar interior: the conductivity rises from 3·10?4 mho/m at a depth of 170 km to 10?2 mho/m at 1000 km depth. The static magnetization field induction has been measured and the whole-Moon relative magnetic permeability has been calculated to be μμ0 = 1.01 ± 0.06. The remanent magnetic fields, measured at Apollo landing sites, range from 3 to 327 γ. Simultaneous magnetometer and solar wind spectrometer measurements show that the 38-γ remanent field at the Apollo 12 site is compressed to 54 γ by a solar wind pressure increase of 7·10?8 dyn/cm2. The solar wind confines the induced lunar poloidal field; the field is compressed to the surface on the lunar subsolar side and extends out into a cylindrical cavity on the lunar antisolar side. This solar wind confinement is modeled in the laboratory by a magnetic dipole enclosed in a superconducting lead cylinder; results show that the induced poloidal field geometry is modified in a manner similar to that measured on the Moon. Induction concepts developed for the Moon are extended to estimate the electromagnetic response of other bodies in the solar system.  相似文献   

4.
Tritium is measured as a function of depth in a Surveyor 3 sample. The upper limit for solar-wind-implanted tritium gives a3H/1H limit for the solar wind of 1 × 10?11. The temperature release patterns of14C from lunar soils are measured. The14C release patterns from surface soils differ from a trench bottom soil and gives evidence for the presence of14C in the solar wind with a14C/1H ratio of approximately 4 × 10?11. The implications of these radio nuclide abundances in the solar wind are discussed.  相似文献   

5.
Both lunar transient phenomena and 222Rn/210Po anomalies observed by Apollo-15 and -16 orbital alpha spectrometers display preferences for certain kinds of locations: rims of circular maria and craters with central peaks and/or dark floors. If these classes of observations are due to lunar gas venting, why are these types of locations preferred? The hypothesis offered is that these are locations at which cracks or channels exist extending deep enough into the moon to tap lunar volatile reservoirs. Possible channels include circumferential cracks around circular maria, old lava tubes for dark-floor and volcanic central peak craters, and shattered subsurface rock structure for impact central peak craters.  相似文献   

6.
Lunar transient phenomena have been attributed to the release of gases from within the moon. The failure of the Apollo surface experiments to detect significant atmospheric enhancements can be used to establish upper limits to the amount of gases now being released from the various sites associated with lunar transient phenomena. An analysis of the sensitivity of the network of Apollo Suprathermal Ion Detector Experiments (deployed initially in 1969 and still operating) indicates that they would have detected any contemporary gas release greater than 6,500 kg from Alphonsus, 28,000 kg from Aristarchus, and similar quantities from other craters. The quantity of gas required to cause such phenomena as obscurations or glow discharge is probably much greater than these values. Consequently, if transient phenomena are real lunar surface events, they must originate from a mechanism other than simple gas emission.  相似文献   

7.
Some breccias from the lunar highlands have probably trapped solar wind gases at a very early epoch in the history of the moon, as implied by their high contents of parentless fissiogenic xenon and sometimes, of parentless radiogenic129Xe. Four samples of this type, on which noble gas data already exist, have been selected for analysis of nitrogen contents and isotopic composition, by using step-wise heating techniques: 14047, 14055, 14307, 60255. Since uncertainties in the evolution of the solar wind15N/14N ratio with time are due in part to uncertainties in the measurement of the epoch of exposure, those samples provided the opportunity to measure the isotopic composition of nitrogen which has been trapped in the remote past, avoiding the problems inherent in the use of spallogenic nuclides. Results show that, in the samples studied from the Apollo 14 landing site, nitrogen is not particularly light, and has not been acquired, as a whole, in very ancient times. The conflicting presence of both parentless xenon and nitrogen of relatively “recent” isotopic signature can be explained if the hypothetical light nitrogen is diluted by more abundant, heavier nitrogen. Accordingly, the very ancient soil components which are implied in these objects by the presence of excess fission xenon have been re-exposed at a much later epoch, or mixed with some younger soil components, before the compaction event. The present data do not question the hypothesis of a secular isotopic variation of lunar trapped nitrogen, but cannot prove that very light nitrogen was trapped together with parentless fission xenon in the soil components of the highlands soil breccias. The very unusual release pattern of nitrogen in breccia 60255 can result from nitrogen isotopic homogenization with gas loss.  相似文献   

8.
The theoretical motion of individual dust grains in the lunar regolith is analyzed by using a Monte Carlo statistical code where the variables are the mass and speed distribution of meteorites at the lunar surface and the geometrical shape of impact craters. From these computations the detailed irradiation history of the grains in the ancient solar wind is traced back, over a period of 4 billion years, as a function of the grain size. Then by combining this irradiation scheme with the result of solar wind simulation experiments, the time and depth dependent accumulation of solar wind effects in the theoretical grains (solar wind maturation) is inferred. Finally, the validity of these predictions is tentatively checked by discussing a variety of physical and chemical solar wind effects which are registered in the surface layers of lunar dust grains. Therefore these studies give a tentative scenario for the “maturation” of the lunar regolith with respect to solar wind effects, but they also reveal useful guidelines to deduce meaningful information from such effects. In particular, they suggest a “lunar skin” sampling technique for extracting dust grains in lunar core tubes which could help in deciphering the past activity of the ancient solar wind over a time scale of several billion years.  相似文献   

9.
The Sm-Nd systematics of lunar KREEP basalt 15386 reflects two chronologically distinct events in the development of the incompatible element-rich materials of the moon. The measured Sm-Nd mineral isochron of 15386 indicates an age of 3.85 ± 0.08 AE which is consistent with the reported Rb-Sr and39Ar-40Ar ages of many other KREEP-rich samples. This age is interpreted as the time at which 15386 crystallized from a liquid on or near the lunar surface. The frequent occurrence of this age for KREEP-dominated samples, as well as the restricted location of KREEP near major lunar near-side impact basins, suggests that the eruption of these incompatible element-rich liquids was related to deep impact events during the postulated final bombardment phase of the surface of the moon. However, the lower than chrondritic initial143Nd/144Nd of 15386 and the essentially identical Sm-Nd evolution of other KREEP-rich samples require that the light REE enrichment which characterizes KREEP was established considerably before 3.85 AE. Within the limits imposed by model assumptions in the various radiometric systems, it is concluded that the extremely narrow spread of Sm-Nd model ages for these samples around 4.36 AE, and the compatibility of this age with that indicated by the U-Pb and Rb-Sr systems, indicate that the source of later KREEP volcanism was produced in the closing stages of an early global scale lunar differentiation episode.  相似文献   

10.
A study of 19 months of data shows that relative variations in the dayside lunar ionosphere are predictable from solar wind flux and solar extreme ultraviolet variations. Discrepancies in the absolute magnitudes exist, however. One significant discrepancy in the predicted and observed ion flux magnitudes probably arises from sputtered surface gases during and following an extended period of anomalously high solar wind flux. A second minor enhancement of the observed flux over the predicted flux may be due to endogenous lunar gas associated with an interval of high lunar seismic activity. However, considerable restraint is necessary in this interpretation since the enhancement is not strong and the interval follows within a few months after the Apollo-17 mission.  相似文献   

11.
If the Earth was formed by accumulation of rocky bodies in the presence of the gases of the primordial solar nebula, the Earth at this formation stage was surrounded by a massive primordial atmosphere (of about 1 × 1026 g) composed mainly of H2 and He. We suppose that the H2 and He escaped from the Earth, owing to the effects of strong solar wind and EUV radiation, in stages after the solar nebula itself dissipated into the outer space.The primordial atmosphere also contained the rare gases Ne, Ar, Kr and Xe whose amounts were much greater than those contained in the present Earth's atmosphere. Thus, we have studied in this paper the dissipation of these rare gases due to the drag effect of outflowing hydrogen molecules. By means of the two-component gas kinetic theory and under the assumption of spherically symmetric flow, we have found that the outflow velocity of each rare gas relative to that of hydrogen is expressed in terms of only two parameters — the rate of hydrogen mass flow across the spherical surface under consideration and the temperature at this surface. According to this result, the rare gases were dissipated below the levels of their contents in the present atmosphere, when the mass loss rate of hydrogen was much greater than 1 × 1017 g/yr throughout the stages where the atmospheric mass decreased from 1 × 1026 g to 4 × 1019 g.  相似文献   

12.
We performed nitrogen and argon isotopic analyses in single 200-μm-sized ilmenite grains of lunar regolith samples 71501, 79035 and 79135. Cosmogenic and trapped components were discriminated using stepwise heating with a power-controlled CO2 laser. Cosmogenic 15N and 38Ar correlate among different ilmenite grains, yielding a mean 15Nc/38Arc production ratio of 14.4±1.0 atoms/atom. This yields a 15N production rate in bulk lunar samples of 3.8-5.6 pg (g rock)−1 Ma−1, which agrees well with previous estimates. The trapped δ15N values show large variations (up to 300‰) among different grains of a given soil, reflecting complex histories of mixing between different end-members. The 36Ar/14N ratio, which is expected to increase with increasing contribution of solar ions, varies from 0.007 to 0.44 times the solar abundance ratio. The trapped δ15N values correlate roughly with the 36Ar/14N ratios from a non-solar end-member characterized by a 36Ar/14N ratio close to 0 and variable but generally positive δ15N values, to lower δ15N values accompanied by increasing 36Ar/14N ratios, supporting the claim of Hashizume et al. (2000) that solar nitrogen is largely depleted in 15N relative to meteoritic or terrestrial nitrogen. Nevertheless, the 36Ar/14N ratio of the 15N-depleted (solar) end-member is lower than the solar abundance ratio by a factor of 2.5-5. We explain this by a reprocessing of implanted solar wind atoms, during which part of the chemically inert rare gases were lost. We estimate that the flux of non-solar N necessary to account for the observed δ15N values is comparable to the flux of micrometeorites and interplanetary dust particles estimated for the Earth. Hence we propose that the variations in δ15N values observed in lunar regolith can be simply explained by mixing between solar wind contributions and micrometeoritic ones infalling on the Moon. Temporal variations of δ15N values among samples of different antiquities could be due to changes in the micrometeoritic flux through time, in which case such flux has increased by up to an order of magnitude during the last 0.5 Ga.  相似文献   

13.
The rate of escape of 40Ar from the moon is calculated from mass-spectrometer data obtained at the Apollo-17 landing site. It is shown that the rate of loss of Ar from the moon varies significantly over periods the order of one lunation and that the average loss rate is about 3 t/a, corresponding to about 6% of the present rate of Ar production by K decay within the moon. These features of the Ar loss-rate data are interpreted as evidence that this gas originates in the partially molten asthenosphere, which in turn requires that early differentiation only affected the outer 600–1,000 km of the moon, trapping significant amounts of radioactive materials in the present asthenosphere. The relationship of the venting of Ar and other radiogenic gases of the lunar atmosphere are discussed.  相似文献   

14.
Abundances and isotopic compositions of all the stable noble gases have been measured in 19 different depths of the Apollo 15 deep drill core, 7 different depths of the Apollo 16 deep drill core, and in several surface fines and breccias. All samples analyzed from both drill cores contain large concentrations of solar wind implanted gases, which demonstrates that even the deepest layers of both cores have experienced a lunar surface history. For the Apollo 15 core samples, trapped4He concentrations are constant to within a factor of two; elemental ratios show even greater similarities with mean values of4He/22Ne= 683±44,22Ne/36Ar= 0.439±0.057,36Ar/84Kr= 1.60±0.11·103, and84Kr/132Xe= 5.92±0.74. Apollo 16 core samples show distinctly lower4He contents,4He/22Ne(567±74), and22Ne/36Ar(0.229±0.024), but their heavy-element ratios are essentially identical to Apollo 15 core samples. Apollo 16 surface fines also show lower values of4He/22Ne and22Ne/36Ar. This phenomenon is attributed to greater fractionation during gas loss because of the higher plagioclase contents of Apollo 16 fines. Of these four elemental ratios as measured in both cores, only the22Ne/36Ar for the Apollo 15 core shows an apparent depth dependance. No unambiguous evidence was seen in these core materials of appreciable variations in the composition of the solar wind. Calculated concentrations of cosmic ray-produced21Ne,80Kr, and126Xe for the Apollo 15 core showed nearly flat (within a factor of two) depth profiles, but with smaller random concentration variations over depths of a few cm. These data are not consistent with a short-term core accretion model from non-irradiated regolith. The Apollo 15 core data are consistent with a combined accretion plus static time of a few hundred million years, and also indicate variable pre-accretion irradiation of core material. The lack of large variations in solar wind gas contents across core layers is also consistent with appreciable pre-accretion irradiation. Depth profiles of cosmogenic gases in the Apollo 16 core show considerably larger concentrations of cosmogenic gases below ～65 cm depth than above. This pattern may be interpreted either as an accretionary process, or by a more recent deposition of regolith to the upper ～70 cm of the core. Cosmogenic gas concentrations of several Apollo 16 fines and breccias are consistent with ages of North Ray Crater and South Ray Crater of ～50·106 and ～2·106 yr, respectively.  相似文献   

15.
The general features of the region of interaction of the solar wind with the ionosphere of Venus and Mars are compared using data obtained with the Mariner 5 and the Pioneer Venus Orbiter (PVO) spacecraft for Venus and with the Phobos II, the Mars Global Surveyor (MGS) and the Mars Express spacecraft for Mars. Despite the overall weak intrinsic global magnetic field that is present in both planets there are significant differences in the manner in which the interplanetary magnetic field accumulates and is organized around and within their ionosphere. Such differences are unrelated to the crustal magnetic field remnants inferred from the MGS measurements around Mars. In fact, while in Venus and Mars there is a region in which the magnetic field becomes enhanced as it piles up in their plasma environment it is shown that such a region exhibits different regimes with respect to changes in the ion composition measured outside and within the ionosphere. At Venus the region of enhanced magnetic field intensity occurs in general above the ionopause which represents the boundary across which there is a change in the ion composition with dominant solar wind protons above and planetary O+ ions below. At Mars the region of enhanced magnetic field is located below a magnetic pileup boundary across which there is also a comparable change in the ion composition (solar wind protons above and planetary O+ ions below). It is argued that this difference in the relative position of the region of enhanced magnetic field with respect to that of a plasma boundary that separates different ion populations results from the peculiar response of the ionosphere of each planet to the oncoming solar wind dynamic pressure. While at Venus the peak ionospheric thermal pressure is in general sufficient to withhold the incident solar wind kinetic pressure there is a different response in Mars where the peak ionospheric thermal pressure is in general not large enough to deviate the solar wind. In this latter case the ionosphere is unable to force the solar wind to move around the ionosphere and as a result the oncoming electron population can reach low altitudes where it is influenced by neutral atmospheric particles (the solar wind proton population is replaced at the magnetic pileup boundary which marks the upper extent of the region where the interplanetary magnetic field becomes enhanced). Peculiar conditions are expected near the magnetic polar regions and over the terminator plane where the solar wind is directed along the sides of the planet.  相似文献   

16.
A large number of individual enstatite crystals of the gas-rich aubrites Khor Temiki, Staroe Pesyanoe and Bustee was analyzed for implanted helium and for steep gradient ion tracks in order to investigate the relation between solar flare irradiation and solar wind implantation with extreme local resolution. Irradiated and non-irradiated crystals coexist within the gas-rich phases of the aubrites investigated. Statistically in a given meteorite the proportion of crystals with implanted solar wind is similar to the proportion of solar flare irradiated crystals. It varies from aubrite to aubrite in the sequence of their bulk contents of trapped rare gases.For nine enstatites, tracks and rare gases were subsequently measured within the same crystal. The results support the intimate association of solar flare tracks and implanted He. The4He-surface concentrations of irradiated crystals vary between <5 × 10?7 and 10?4 cm3 STP/cm2.The absence of saturation effects together with the low degree of elemental gas fractionation indicates very short solar wind exposure times (< 100 yr) rather than strong diffusion losses. The evidence from tracks and rare gases can be understood in terms of an early simultaneous irradiation of aubritic crystals by solar wind and solar flare particles on top of a regolith-covered parent body.  相似文献   

17.
The composition, structure and evolution of the moon's interior are narrowly constrained by a large assortment of physical and chemical data. Models of the thermal evolution of the moon that fit the chronology of igneous activity on the lunar surface, the stress history of the lunar lithosphere implied by the presence of mascons, and the surface concentrations of radioactive elements, involve extensive differentiation early in lunar history. This differentiation may be the result of rapid accretion and large-scale melting or of primary chemical layering during accretion; differences in present-day temperatures for these two possibilities are significant only in the inner 1000 km of the moon and may not be resolvable. If the Apollo 15 heat-flow result is representative of the moon, the average uranium concentration in the moon is 0.05–0.08 p.p.m.Density models for the moon, including the effects of temperature and pressure, can be made to satisfy the mass and moment of inertia of the moon and the presence of a low-density crust inferred from seismic refraction studies only if the lunar mantle is chemically or mineralogically inhomogeneous. The upper mantle must exceed the density of the lower mantle at similar conditions by at least 5%. The average mantle density is that of a pyroxenite or olivine pyroxenite, though the density of the upper mantle may exceed 3.5 g/cm3. The density of the lower mantle is less than that of the combined crust and upper mantle at similar temperature and pressure, thus reinforcing arguments for early moon-wide differentiation of both major and minor elements. The suggested density inversion is gravitationally unstable and implies stresses in the mantle 2–5 times those associated with the lunar gravitational field, a difficulty that can be explained or avoided by: (1) adopting lower values for the moment of inertia and/or crustal thickness, or (2) postulating that the strength of the lower mantle increases with depth or with time, either of which is possible for certain combinations of composition and thermal evolution.A small iron-rich core in the moon cannot be excluded by the moon's mass and moment of inertia. If such a core were molten at the time lunar surface rocks acquired remanent magnetization, then thermal-history models with initially cold interiors strongly depleted in radioactive heat sources as a primary accretional feature must be excluded. Further, the presence of ～||pre|40 K in a FeFeS core could significantly alter the thermal evolution and estimated present-day temperatures of the deep lunar interior.  相似文献   

18.
EISCAT observations of interplanetary scintillation have been used to measure the velocity of the solar wind at distances between 15 and 130R (solar radii) from the Sun. The results show that the solar wind consists of two distinct components, a fast stream with a velocity of 800 km s–1 and a slow stream at 400 kms–1. The fast stream appears to reach its final velocity much closer to the Sun than expected. The results presented here suggest that this is also true for the slow solar wind. Away from interaction regions the flow vector of the solar wind is purely radial to the Sun. Observations have been made of fast wind/slow wind interactions which show enhanced levels of scintillation in compression regions.  相似文献   

19.
It has been clearly established that there is a substantial outflow of ionospheric plasma from the Earth's ionosphere in both the northern and southern polar regions. The outflow consists of both light thermal ions (H+ and He+) and an array of energized ions (NO+, O2+, N2+, O+, N+, He+, and H+). If the outflow is driven by thermal pressure gradients in the ionosphere, the outflow is called the “classical” polar wind. On the other hand, if the outflow is driven by energization processes either in the auroral oval or at high altitudes in the polar cap, the outflow is called the “generalized” polar wind. In both cases, the field-aligned outflow occurs in conjunction with magnetospheric convection, which causes the plasma to drift into and out of the sunlit hemisphere, cusp, polar cap, nocturnal auroral oval, and main trough. Because the field-aligned and horizontal motion are both important, three-dimensional (3-D) time-dependent models of the ionosphere–polar wind system are needed to properly describe the flow. Also, as the plasma executes field-aligned and horizontal motion, charge exchange reactions of H+ and O+ with the background neutrals (H and O) act to produce low-energy neutrals that flow in all directions (the neutral polar wind). This review presents recent simulations of the “global” ionosphere–polar wind system, including the classical, generalized, and neutral polar winds. The emphasis is on displaying the 3-D and dynamical character of the polar wind.  相似文献   

20.
Data on the electrical conductivity of olivine and pyroxene obtained under redox conditions similar to those that exist in the moon indicate that the moon is at temperatures near the melting point at depths of 600–900 km. This temperature profile, combined with information on the distribution of radioactive elements and evidence of extensive differentiation of the moon, lead to the conclusion that the moon accreted at temperatures between 600–1000°C. This high accretion temperature can be reconciled with the presence of FeS and the probable FeO/MgO ratio in the lunar interior if the moon accreted from material which was depleted in H2 relative to the solar nebula.  相似文献   

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