Vol 53, No 2 (2019)

Internally consistent models of the thermal state, chemical composition and mineralogy of the three-layer mantle of the Moon are constructed based on the joint inversion of gravity, seismic and petrological-geochemical data within the Na₂O-TiO₂-CaO-FeO-MgO-Al₂O₃-SiO₂ system. Geochemical constraints on the chemical composition and physical properties in three zones of the mantle are obtained in terms of the cold and hot models. Velocities of P-waves in the lower mantle (∼8 km/s) are higher than in the upper mantle (∼7.7 km/s). The behavior of velocities of S-waves is conservative, they are observed in the interval 4.40–4.45 km/s in all zones of the mantle. It was found that, independently of the temperature distribution, the most probable concentrations of FeO, ∼11–14 wt % and MgO, 28–31 wt % and the values of the magnesian number MG# 80–83 are approximately the same in the upper and the lower mantles of the Moon, but drastically differ from those in the bulk composition of the silicate Earth (Bulk Silicate Earth, BSE, FeO 8%, MG# 89). On the contrary, the estimates of Al₂O₃ concentration in the three-layer mantle noticeably depend on the thermal state. The results of solution of the inverse problem indicate the trend towards the gradual increase in the Al₂O₃ content with depth, from the upper to the lower mantle to 4–7% with the higher content of garnet. For the cold models of the lower mantle of the Moon, the bulk content of Al₂O₃ is ∼1 × BSE, and for the hot models it can be in the interval of 1.3 × BSE-1.7 × BSE. The abundance of SiO₂ depends, to a lesser degree, on the thermal state and is 50–55% in the upper and 45–50% in the lower mantle. The high pyroxene content of the upper mantle of the Moon is the geochemical consequence of the geophysical models used with the inversion into composition and temperature relations; orthopyroxene, instead of olivine, is the dominant mineral of the upper mantle. Concentrations of SiO₂ in the lower (undifferentiated) mantle showing the bulk composition of the silicate Moon (Bulk Silicate Moon, BSM), are consistent with the geochemical estimates of 45–48% of SiO₂ for the BSM and close to those for the Earth’s mantle (45–47%). The composition of the mantle middle zone remains discussible, since it might be partially overlapped with compositions of the over- and underlying envelopes. The results of the model suggest that the mantle of the Moon is stratified in chemical composition. For the considered thermal state models, the mantle of the Moon is enriched in FeO and depleted in MgO in relation to the primitive Earth mantle, which indicates considerable differences between compositions of the Earth and its satellite.

Cosmogenic radionuclides with half-life periods T_1/2 ranging from several days to a million years, produced in the nuclear reactions of galactic cosmic rays (GCR) with meteoritic matter, provide valuable information on the GCR intensity variations on a long time scale (∼1 million years) within meteorite orbits 2–4 AU from the Sun. Information on the variations of GCR gradients in the inner heliosphere was obtained by comparing the measured contents of ⁵⁴Mn and ²²Na in stone meteorites (chondrites) with known orbits at the time of their fall to Earth with the calculated production rates of these radionuclides in them using balloon intensity measurements of GCR (E > 100 MeV) in the stratosphere at appropriate times. Although individual gradient values show significant uncertainties, the important information is that cosmogenic radionuclides in chondrites predict low gradients (0–10% per 1 AU) for all periods of minimum solar activity in 1957–2013, according to direct measurements in interplanetary space. High gradients (50–100% per 1 AU) are predicted for periods of maximum solar activity, especially in 1992 and 2012 (up to ∼200% per 1 AU). Average values of gradients are (20 ± 10)% per 1 AU for modern solar cycles (according to the production rate of ²²Na), similar to the average values for the last ∼1 million years (according to the production rate of ²⁶Al), which indicates the constancy of the solar modulation of the GCR, at least for the last million years.

To build the mass distribution of exoplanets discovered with the method of measuring the radial velocities, it is necessary to take into consideration the observational selection factors. We propose the detectability-window method to form homogeneous series of exoplanets. In addition, the errors in determining the masses are taken into account. The mass distributions of the transiting planets and the planets discovered with the radial-velocity method are compared in a range of 0.5 to 13 Jupiter masses.

An overview is given of the scientific and organizational outcomes reached at the 30th General Assembly of the International Astronomical Union, held on August 20–31, 2018, in Vienna, Austria.