The major elements of glassy spherules from samples 12001.73, 12057.60 and 12070.37 of lunar fines have been determined by electron probe analysis. The bulk chemistry of these spherules (which are between 200 μm and 62 μm in size) falls in most cases within the range of gabbro-peridotite and gabbro-anorthosite.

In individual spherules, the grade of chemical homogeneity is highly variable and can be related to the possible presence of small inclusions or sometimes to slight concentration gradients evident near the peripheries of the particles. These features, together with the presence of vesicles of different size in association with strong alkali enrichment along the boundaries of such cavities can account for relationships between the chemistry of the particles and their genetic history.

Glassy spherules ranging from 200 μ to 62 μ in size have been separated from lunar dust samples No. 12001.73, 12057.60, 12070.37. Most of them are regular in size (spherical, ellipsoidic, dumbbell, teardrop, etc.); some are irregularly shaped.

A tentative dynamical model of the evolution of a rotating melted spherical drop of homogeneous glassy material has been built in order to explain the observed forms. We suppose such fluid to be originated from the impact of meteoroids on the lunar surface. The energy balance between the projectile (meteoroid) and the target (lunar surface) has been calculated supposing that the impact gives rise to strong shock waves in both bodies.

Equations of the model have been solved numerically and a good agreement between these results and the experimental data regarding small spherules has been obtained.

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.

One of the possible reasons of the long duration of lunar seismograms are multiple reflections in the upper part of lunar cross-section, similar to those generating under Earth conditions. While registration of seismic oscillations in a region with stratified low-velocity sediment rocks of 6–7 km thickness the authors observed long seismic low-decaying oscillations. The observed decay was about 40 db during 30 min.

The long duration records are obtained only on the distances where the intense overcritical reflections exist from the M-boundary situated at a depth of 50 km.

These waves generated numerous multiple reflections, longitudinal, shear and converted waves in the upper part of the cross-section. These body waves are responsible for the generation of the surface waves, recorded in the subsequent parts of the seismograms. Periods of body waves are about 1–1.5 s., those of surface waves – about 1.5–3 s.

Extrapolating similar mechanism of the wave generation to lunar media, one should assume the presence of a layered upper part of the cross-section and the possibility of the sufficiently intense wave incidence on its lower boundary.

It is possible if either reflecting boundaries or a vertical velocity gradient are present in the underlying media. The first variant is accompanied with overcritical reflections, the second one – with intense refracted waves.

At present seismographs are operating on the Moon as well, installed there owing to the successful Apollo missions. However these data are insufficient for detailed statistic investigations. That is why in case of the Moon we are to use indirect indications of its activity, such as the data on transient light phenomena from the catalogues by Miss B. Middlehurst. Among the great number of earthquakes there were chosen only the strong earthquakes (magnitude 6.5) with focuses deeper than 70 km. According to these characteristics 630 earthquakes were selected from 1904 to 1967. In the Middlehurst catalogue during the same period about 370 transient events on the Moon are registrated. A distribution of lunar events on the days of an anomalistic month gives evidence of the influence of the Earth's tidal forces (the Middlehurst effect). It appears that the distribution of earthquakes gives a similar curve. Thus the tidal interaction of the Earth and the Moon establishes certain synchronism in tectonic activity of these planets. The further statistic analysis reveals some more causal relation between the processes of the Earth and the Moon. Strongly pronounced maximum of lunar events is observed with the interval of 2–3 days after the earthquakes and the maximum of earthquakes – with quite the same interval after the lunar events. The peaks of these maxima exceed the mean number of events by a factor 3. The Moon Earth system is the astronomical example of a direct interaction of the processes in the neighbouring celestial bodies.

The corresponding experiments, made at the Pulkovo Observatory, confirm the possibility of immediate interactions of irreversible processes due to the change of physical properties of time. Thus we can form a chronology of orogenesis on the Moon judging from the data on the history of the Earth. Tectonic processes of the Earth and the Moon seem to be in such a close interaction as if the Moon were in direct contact with the Earth, i.e. in other words, were its seventh continent. These conclusions give evidence of the extreme importance of regular seismic observations on the Moon.

An attempt is made at explaining the successive origin of the central peaks and terrace ring-wall in the crater formations filled with melt after impacts.

The hypothesis on an internal origin of lunar rocks of gabbroic type is supported by experimental petrologic data obtained by the author. The temperature interval of their crystallization from a dry silicate melt is given.

Lunar gabbroic rocks of the Tranquillity Base are compared with paleobasalts of north-eastern Bohemia, eucrites and associated rocks of the British Isles and meteoritic eucrites of poikilophitic texture.

The metasomatic origin of lunar anorthosites displaying a mosaic texture in deeper parts of the volcanic apparatus is postulated.

An analogy is thought to exist between the Tertiary volcanic areas of Mull, Ardnamurchan and Rum in Scotland and the Ptolemaeus, Alphonsus and Arzachel regions of the Moon in the overall tectonic structure and the development of tectono-volcanic cirques. By analogy the possibility of the presence of more basic rocks in the rim and on the floor of the Moon subsidence calderas and of more acidic rocks of anorthositic to trachyandesitic chemistry in the central peak is presumed.

The mode of origin of double-craters of Cyrillus-Theophilus type is suggested to be similar to the origin of two consecutive volcanic rings of Mull.

The ring- and radial complexes of wrinkle ridges of Lamont type are compared with cone sheets and radial dykes of the central type tectono-volcanic complex of Mull.

A review of results obtained by an examination with optical interferometry of a variety of glassy objects found in lunar fines from Apollo 11 and 12. Glassy spheres, cylinders, chips and fragments have been examined. It is established that many spherules show

(a) evidence of shock;

(b) evidence of impact with a small particle;

(c) very high specularity.

Some small pieces of lunar glass reveal the characteristic step pattern shown by glass shattered in the laboratory.

The absorption spectra of Apollo 11 fine-grained rocks, 10017 and 10022 are due entirely to pyroxene minerals. Spectral bands due to Fe3+, Fe2+, Cr3+ and Ti4+ and Ti3+ are detected. Single crystals of olivine in rocks 12021 and 12018 show bands due to Fe3+, Fe2+, Cr3+, Ti3+, Mn3+, and Mn2+. Pyroxenes in the same rocks exhibit band maxima of the same cationic species as in the olivines. Spectral shifts are noted due to anisotrophy of the crystal structures.

Heating sections 10017, 10022, and 12018 from the rock interiors at 200–225°C for 2 h caused large decreases in the spectral intensity of Fe3+, Cr3+ and Ti3+, indicating the following reaction:

Fe3+ + Cr3+ + Ti3+ → Fe2+ + Cr2+ + Ti4+

This suggests that Fe3+, Cr3+ and (a portion of) Ti3+ are not in equilibrium. It is most probable that they were produced subsequent to the formation of the rocks by a combination of secondary ionization processes following cosmic ray bombardment and by trace radioactivity present in the rocks.

An orange glass, 150 μ in diam and 50 μ thick contained in brecciated rock, 10048.44, exhibited 15 identifiable absorption bands related to Fe2+, Cr3+, Ti3+, Mn3+ or Mn2+ ions.

Plagioclase in 12021.65 has perfect transmission over the region studied. The limit of Fe3+ is in the order of < 1 ppm and Fe2+, 1000 ppm or less in this plagioclase single crystal of dimensions 0.6 mm × 0.2 mm × 30 μ.

A proton accelerator, modified for work on lunar samples, is described; 60 keV protons at about 1 μA cm−2 are used. Luminescence emission spectra in the visible and near IR regions are shown for lunar samples from Apollo 11 and 12, and preliminary results are given for Apollo 14 samples. Lunar samples are compared with terrestrial and meteoritic materials. Plagioclase is found to be the most efficient luminescent material present in the lunar samples, and the activator for its dominant green peak is found to be Mn2+.

Apparatus is described for taking colour photographs of the luminescence emission from rock chips under 6 keV electron excitation. Most of the lunar samples investigated show only plagioclase emission, but one breccia shows a wide variety of colours from different luminescent constituents.

Comparative studies of the distribution of latent and etched tracks in lunar grains from five different size fractions of three lunar fine samples and of six lunar dust samples taken at different depths in core tube 12028 have been performed by using transmission and scanning electron microscopies. Two very different sets of etching conditions were used: a slight etching was applied for transmission microscopy but a much stronger etching was used for scanning microscopy. We observed: (1) a definite stratigraphy in the core tube, both in the latent and etched track distributions; (2) striking differences between the densities of the latent and slightly etched tracks (≥ 1010 tracks cm−2) and those of the strongly etched tracks, ranging from ⋍ 108 to 5.109 tracks cm−2; (3) a lack of correlation between the grain size and the density of strongly etched tracks observed on the external surface of grains from sample 12032; (4) no variation of the density of the tracks with the depth inside a grain. Some implications of the present results concerning the ancient low energy solar cosmic rays and the fabric of the lunar soil will be briefly discussed.

We have studied by combined high voltage and scanning electron microscopies both the latent and etched track distributions in lunar fragmental rocks as well as in solar type gas-rich meteorites. We have used a new experimental approach for studying gas-rich meteorites to avoid problems with the interpretation of the results. Some implications of the present results concerning the ancient solar flare cosmic rays and the origin of the track distributions in gas-rich meteorite crystals will be discussed.

Studies of thermoluminescence emission from lunar samples show that at lunar day surface temperatures and even at 18°C the trapped electron responsible are decaying to their ground states by a non-thermal process. Data from various workers show similar characteristics with respect to this process. They show that thermoluminescence cannot be used as a technique for dating lunar samples (or terrestrial plagioclases) over any significant geological period. A quantitative model for the non-thermal process is proposed.

Information about lunar surface history revealed by fossil particle tracks is summarized. Such tracks are the result of damage left in dielectric materials by highly ionizing charged particles including heavy solar and galactic cosmic ray nuclei, heavy nuclei recoiling from cosmic ray induced spallation reactions and induced- and spontaneous-fission fragments. From the distribution of cosmic ray and spallation tracks in the lunar rock, surface residence times of 1 to 30 million yr and rock erosion rates of 1 to 10 Å/yr have been determined. Particle tracks also record surface orientation and depth history of the rocks and contain information about ancient solar activity. The distribution of particle tracks in lunar soil is found to be consistent with a model which includes repeated excavation, layering and burial. With this model one core 12025 + 28 soil layer can be identified as unmixed and weakly irradiated; the others contain soil which has been better and better mixed and more and more irradiated.

Steady magnetic field measurements of magnitude 30 to 100 γ on the lunar surface impose problems of interpretation when coupled with the non-detectability of a lunar field at 0.4 lunar radius altitude and the limb induced perturbations of the solar wind reported by Mihalov et al. at the Explorer orbit. The lunar time varying magnetic field clearly indicates the presence of eddy currents in the lunar interior and allows calculation of an electrical conductivity profile. The problem is complicated by the day-night asymmetry of the Moon's electromagnetic environment, the possible presence of the TM mode and the variable wave directions of the driving function. The electrical conductivity is calculated to be low near the surface, rising to a peak of 6 × 10−3Ω−1 m−1 at 250 km, dropping steeply inwards to a value of about 10−5Ω−1 m−1, and then rising toward the interior. A transition at 250 km depth from a high conductivity to a low conductivity material is inferred, suggesting an olivine-like core at approximately 800 °C, although other models are possible.

During the next Apollo mission Apollo 15, it is planned to fix thermocouples at various depths up to 3 m below the lunar surface. It seems likely that the resulting temperature measurements will show a positive temperature differential with depth resulting from a net outward heat flux. It is the purpose of this paper to examine experiments already carried out which indicate a temperature gradient. Since the thermal flux is of direct importance in fundamental problems of lunar origin and the nature of the lunar interior, the relation between this quantity and the temperature gradient will be examined.

It is natural to inquire whether thermal convection is occurring in the Moon through solid state creep processes. The primary evidence is the departure of the Moon from the figure of hydrostatic equilibrium, but certain difficulties in the thermal history of the Moon are eased by assuming heat transfer by convection. If convection exists in the Moon it must have a second harmonic pattern, otherwise the lunar moments of inertia would not differ.

Two important predictions of the marginal theory of convection: the existence of a core of radius 0.06–0.3 of the lunar radius (for a second ergee harmonic) and the value of 0.4 for the ratio of the dynamical to surface ellipticities now have support, the latter from the data of the heights of the lunar surface. The former prediction is compatible with the value of the moment of inertia factor now found if the Moon's interior is ‘hot’.

Further the existence of a fluid iron core 3400 m.y. ago seems required as a result of the remanent magnetization of the crystalline rocks of the maria basins inferred from the remanent magnetization of the returned Apollo samples and the fields measured by the Apollo 12 and Explorer magnetomers.

The possible thermal history of the Moon is investigated by means of theoretical models. The calculations include the effects of melting and time-dependent redistribution of radioactive heat sources. The known constraints can best be satisfied by a model which is characterized by relatively high initial temperatures close to the melting range; melting and, consequently, fractionation and redistribution of radionuclides would occur during the first 1.5 × 109 yr and would then be followed by an effective cooling process. Heat flow measurements on the lunar surface should permit a distinction between such a completely fractionated model and a non-fractionated model or a model with restricted fractionation in the outer few hundred kilometers.

Analyses of occultation timings show that periodic correction terms with semi-amplitude as great as 0.″18 arise from corrections required to the empirical constants of the Brown/Eckert theory. Using the atomic time-scale, some of the occultation data have been used to determine a correction of – 30 ± 16″/cy2 to Spencer Jones' value for the secular acceleration of the Moon. In the light of this correction, and previous determinations, attention is drawn to the possible weakness of Spencer Jones' value, which is not reflected in his quoted error of ± 1″/cy2. Further analyses of 50000 occultations observed since 1943 promise to reveal more accurately-determined corrections.

According to the Radzievskij-Artemjev hypothesis of the ‘locked’ revolution of the circumplanetary swarms around the Sun, the initial Moon-to-Earth distance and the angular momentum acquired by the Earth through the accretion of the inner part of the swarm can be evaluated. Depending on the concentration of the density to the centre of the swarm we obtain the initial distance for a single protomoon in the range 15–26 Earth radii R and for a system of 3-4 protomoons in the range 3–78 R, if the outer boundary of the swarm equals to the radius of the Hill's sphere (235 R). The total angular momentum acquired by the primitive Earth-Moon system through the accretion of the swarm particles is ½–⅔ of its present value. The rest of it should be acquired from the direct accretion of interplanetary particles by the Earth. The contribution of satellite swarms into the rotation of other planets is relatively less.