Moon, moons and planets of Solar system

A.V.Gusev, Yu.A.Nefedyev

EAO, Kazan Federal University

Russia

The article gives brief account of reports presented at the International symposium "Moon, satellites of planets and planets: Robotic exploration and comparisons" which took place within the framework of the timed to the International Year of Astronomy international astronomical congress "ASTROKAZAN-2009" organized under the aegis of UNESCO and hosted by Kazan State University (Kazan, August 21-26, 2009). The majority of reports had to do with the study of the Moon and planets and results of numerous lunar satellite missions during 2006-2009. International symposium "Moon, satellites of planets and planets: Robotic exploration and comparisons" (chairman of Scientific Organizing Committee academician M.Marov). Symposium was dedicated to recent studies of the Solar system and results of various space experiments. The work was organized in two plenary sections. Section A: Planets and moons of Solar system; Section B: The Moon: Yesterday, Today, Tomorrow. Seminar participants - delegates from eight foreign countries, including especially representative delegations from Japan and France discussed achievements, problems and prospects of research of the Moon, Mars, Mercury, Venus, satellites of Jupiter and Saturn. Special attention was paid to lunar research and the results of numerous lunar missions, and this is not by mere chance, as Kazan school of astronomy is widely recognized by the world scientific community for significant achievements lunar research.

Symposium was also dated to the 50-year anniversary of lunar research in Russia. On January 2, 1959, the Soviet Union startled the world by launching first-ever automatic space station "Mechta" towards the Moon. The station flew by the Moon at a distance of 6000 and having left the sphere of terrestrial gravitation on January 4 became the first man-made object to reach heliocentric orbit. "Mechta" for the first time ever managed to reach second cosmic velocity and obtained information about the radiation belt of the Earth. The second lunar probe launched on September 14 of the same year, reached the lunar surface and delivered pennants with depictions of the national emblem of the USSR. Just one month after "Luna-3" equipped with the camera, transmitted to the Earth shots of the invisible from the Earth side of the Moon. In 1966 the Soviet Union launched "Luna-9" which for the first time in history achieved lunar soft landing and launched the first artificial satellite of the Moon "Luna-10", having conceded, however, to Americans a palm tree of superiority in piloted flights to the Moon. Nevertheless, almost simultaneously with the "Apollo" program flights of American astronauts, Soviet automatic stations "Luna-16, -20 and -24" delivered to the Earth samples of lunar soil from several sites of the Moon, whereas self-propelled rovers "Moon rover 1 and 2" worked on a lunar surface for more than one and a half year and collected unique scientific material. These historical achievements made under the supervision of our outstanding engineer G.N.Babakin, have not been yet outrivaled nowhere in the world.

Symposium participants discussed further development of lunar research and the active role of Kazan State University and its astronomical observatory named after V.P.Engelgardt. At present active work is being done within the framework of scientific and technical cooperation agreement between KSU and National observatory of Japan, drawing on data sets received from the Japanese satellite "Kaguya" in 2007-2009 which obtained the precise topography map of lunar surface, including earlier unknown areas of southern and northern poles of the Moon and a map of surface distribution of gravitational fields and gravitational anomalies of the backside of the Moon.

With the help of the onboard laser altimeter "Kaguya" mapped heights of 6,8 millions points on the surface of the Moon, including polar zones, with the range accuracy within 4 m. It also scanned the lunar poles which are permanently shaded from the sun. The difference between the highest and lowest surface points was revised to about 19,8 km, which is 2 km more than its was earlier suspected. The highest elevation on the Moon is the southern rim of Dirichlet-Jackson basin (about 11 km), whereas the lowest is inside Antoniadi crater (-9.06 km) in the Aitken Basin at the South Pole. On the far side a number of topographically ring-shaped negative gravity anomalies were detected. The latter often contain smaller positive gravity anomalies. The given ring-shaped negative anomalies associate with low-density rocks. Unfortunately, the origin of these positive anomalies remains unknown. They can be craters filled with volcanic basalts or solidified mantle rocks elevated in the result of collision with comets and large meteorites. Drawing on recently obtained information about on roughness of both visible and invisible sides of the Moon, it turned out possible to calculate rigidity of lunar crust and upper mantle. In opinion of the authors of research, nowadays the Moon has scarce reserves of water ice, and, most likely, it never had too much water neither on its surface, nor in the thick lunar crust.

Below is a brief review of the most interesting reports and presentations delivered at Symposium. In his introductory report "Lunary-planetary research. A glance from Russia" academician M.Marov presented a detailed overview of Solar system research over the last decade, briefly discussed most significant results are reviewed immediate prospects of domestic program in accordance with the plans of the Russian Federal Space Agency. In his report "SMART-1 mission results and the future of lunar research" Dr. Bernard Foing, Executive Director of the International Lunar Exploration Working Group (ILEWG) of the European Space Agency have considered several samples of hi-tech space equipment, the results of research of the surface of the Moon done in 2003-2006 by SMART-1 spacecraft and extensive international plans of lunar research up to 2020 within the framework of international cooperation.

Two reports of Japanese colleagues Dr. N.Namiki et al. "Comparative study of compensation mechanism of lunar impact basins from new gravity field model of Selene (Kaguya)", and H.Araki et al. "Lunar global topographic map by the Kaguya laser altimeter" were of special interest: scientists presented high-precision global and local gravitational and topographical maps of the Moon. They have also exemplified their use for construction of models of simulation of formation of impact craters on the surface of the Moon. Future research prospects were discussed in the report Dr.H.Hanada's (Japan) report "Various kinds of observation of lunar rotation and gravity by SELENE-2", such as observation of physical libration of the Moon with the help of a telescope to be installed on the Moon's pole in 2014 (program ILOM, mission SELENE-2). This telescope with 1m focal distance and aperture of 20 cm will be equipped with 4000x4000 CCD array to allow for determination of the stellar position accurate to one milliarcsecond. According to the results of computer generated simulation, during 450 days 14 basic members of the forced physical libration will be available for observation at the maximum accuracy of 1 milliarcsecond. These experiments will help to measure lunar core's radius R_c and density, density jump at core-mantle boundary, as well as its ellipticity, to obtain parameters of free libration and differential rotation of core and mantle.

S.Kopeikin (University of Missouri, USA) reported on "Millimeter Laser Ranging to the Moon: a comprehensive theoretical model for advanced data analysis" within the framework of the international project aimed at theoretical developments necessary to create ranging technologies allowing measuring Earth-to-Moon distance with the accuracy of up to 1 mm. The given task can be solved with regard to relativistic effects of rotation of the Earth-Moon system and recent achievements in geophysics and selenophysics. So far, the measurement error is 13 mm. More accurate knowledge of complex laws of rotation of the Moon will allow for clarification of fundamental physical constants of the general theory of relativity, sophisticated structure and composition of the Moon's core and a viscous-elastic mantle. O.Kuskov, corresponding member of the Russian Academy of Science presented very interesting report "Joint inversion of seismic and petrologic data for lunar thermal state". According to O.Kuskov, upper and lower layers of the Moon's mantle are amazingly different, pyrolitic model of lunar mantle cannot be adopted as a geochemical-geophysical basis for the entire mantle, whereas the structure of the Moon's mantle differs from the structure of the upper mantle of the Earth. The author concludes, that composite effects of rocks' composition play the dominant role in determination of temperatures from seismic models, whereas the obtained temperature profiles allow to define not only the range of admissible lunar mantle temperatures, but also boundaries of geophysical parameters by certain range of reasonable mineralogical structures and velocity models of the Moon.

Several joint reports by A.Gusev and N.Petrova and their Japanese and Russian colleagues under the common title "Rotation, physical libration and internal structure of multilayered Moon" discussed problems of study of subtle effects of rotary movement - physical libration, diverse internal structure of the Moon, research of gravitational field of the Moon and planets by methods of inter-satellite tracking and free libration of the Moon and planets. Identification of periods and amplitudes of free libration will allow to draw a conclusion about the presence of a liquid core of the Moon and planets, appreciate the size, the form, structure and temperature profile, as well as periods of Chandler wobble of inner solid core and free nutation of inner fluid and inner solid cores of the Moon. For the first time ever, authors calculated the spectrum of free libration and accomplished structural-parametrical modeling of the internal structure of the Moon aimed at the definition of dependence of the received periods of free rotation from radius, density, chemical composition of the core, as well as from dissipative characteristics of the core-mantle zone. Apart from the presented simulative geophysical profile of the Moon and structural specification of lunar two-layer core, of special interest were the results of star tracks simulation to be used in the course of organization of observations with the help of a polar optical telescope to be installed on one of the poles of the Moon within the framework of the Japanese ILOM project scheduled for 2010-2014. Separate project of estimations and recommendations relating to observation of physical libration of the multilayered Moon was presented. Modern fundamental problems of international astronomical and geophysical research of the Moon have been formulated with regard to prospects of creation of permanent manned lunar bases. Concept of lunar navigation yearbook was presented. Professor Yu.Barkin et al. reported on "First-order disturbances in rotation of the Moon" and presented the analytical theory of forced libration for the non-spherical solid Moon. At a first approximation for major angular variables of the theory of PoincarÊ and Euler and for various dynamic parameters of the Moon tables of amplitudes, phases and frequencies of physical libration were received.

E.Kozlova et al. in "Study of the relief of the South Pole basin of the Moon" compared topographical data from the South Pole of the Moon received by different recent lunar missions. Drawing on information obtained by the Japanese probe Kaguya (2007-2009) the authors of the report have reconstructed the three-dimensional relief and sun exposure maps of the South Pole of the Moon which will be very useful for planning future lunar projects.

New analytical approach to the study of physical libration of the solid-state Moon with regard to disturbances from the Earth and the Sun, based on 12 Euler equations for 15 variables, has been presented and analyzed by B.Kondratiyev in his report "Vector approach to physical libration of the Moon". In the result of transformations and linearization of the equations, he received the general solution - superposition of independent libations by longitude and latitude.

First report of M.Shpekin "Topographical preparation of airfields on the backside of the Moon" contained the analysis of morphology of the backside of the Moon in terms of its suitability for automatic spacecrafts' landing. Among the analyzed sites are East sea zone (the edge zone of the Moon) and sites at Aitken and Tsiolkovsky craters. Author also considers questions related to verification of topography of the proposed landing sites with reference to digital photogrammetry of photo shots of the abovementioned territories explored in 1968-70 by the Soviet spacecrafts "Probe-6,-8" and in 1970-72 by crews of American "Apollo-15,-16,-17". Second report "Study of Tsiolkovsky crater" focused on two new objects discovered by M.Shpekin at the bottom of the given crater. This interesting research project started with the photo shots of Tsiolkovsky crater made at the last orbit pass of "Apollo-17" while the sun was setting down the lunar horizon. Pictures were digitized at the University of Arizona and then first published in the spring of 2009. The has published his first paper on the found objects in June of 2009, two days before Americans launched their LRO (Lunar Reconnaissance Orbiter). The first object is the "oval plump hole" of about 24 km in diameter at the bottom of the crater. The second object is a small volcano next to the center of the abovementioned oval. Next series of appreciable and important reports was dedicated to urgent problems of planetary research with regard to future space projects, as well as fundamental cosmogony problems and computer-generated simulation tasks.

Academician L.Zelenyi et al. in "Landing to Europe: scientific goals and experiments" reviewed the basic data of Europe, Jupiter's moon, the purposes objectives of the international LAPLACE mission planned for 2020, and the list of most significant experiments to be implemented from Europe's orbit and after landing of the spacecraft on its surface. Its main goal is to look for evidence of a possible subsurface ocean and to estimate its properties. The report comments upon modern conceptualization of Europe's relief and internal structure, as well as some technical issues related to the space vehicle design and sequential formation of its orbit with a view to guarantee successful execution of all landing operations. Preliminary results of future research project were presented at the international conference ("Europe Lander: science goals and experiments", February 9-13, 2009) hosted by the Space Research Institute (Moscow, Russia).

J.Souchay and L.Cottereau's from the Paris observatory reported on "The rotation of Venus: state-of-the-art and precession-nutation model". The authors delivered historical overview of existing theories of rotation of Venus drawing on observations data and discussed the problem of variations of axis' inclination and reverse rotation. Most interesting are the results of numerical modeling of rotation of Venus for different models of its internal structure with regard to tidal effects' influence and dense atmosphere on variations of speed of rotation of the planet, as well as study of resonance between precession and orbital variations. Hamiltonian theory of nutation by longitude and in inclination with regard to all possible geophysical effects has been constructed at a first approximation.

In his detailed report Prof. O.Korablev "Spacecraft observations of Mars: Recent achievements and plans for the future" discussed results of recent Mars-related research projects received based on high-precision data of optical measurements in a wide range of frequencies received from numerous satellites and landing modules, mainly, from the European "Mars-Express" space vehicle. The latter was equipped with instruments developed jointly by Russian and European scientists. Close attention has been paid to precision spectrometry, laser altimetry, mineralogical analysis of mantle rocks, content and distribution of water in the near-surface layer and in atmosphere, and magnetic measurements. Future Russian, American and European space projects aimed at detailed exploration of Mars' nature and evolution were discussed.

Results of long-term measurements of content of water,            carbon dioxide, ozone and aerosols in the atmosphere of Mars with the help a multipurpose spectrometer were presented in A.Fedorova's et al. report "Infrared measurements with SPICAM experiment on Mars-Express: three Martian years of observations of the Martian atmosphere". The authors also considered reserves of water and carbon-dioxide ("dry") ice in the near-surface layer and received numerous distributions of concentrations of the abovementioned elements by latitude, longitude and altitude. So far, it is the applied work only. Academician M.Marov et al. in "Modeling of evolution of the protoplanetary gas-dust circumsolar disk" considered conceptual questions and results of computer-generated simulation of the structure and early evolution of the circumsolar protoplanetary disk based on methods of heterogeneous mechanics of turbulent environments. Main attention was paid to models of thermal and dynamic evolution of the protoplanetary with regard to radiation transfer and turbulence in gas-dust environment, calculation of variations of thermal conditions in a zone of formation of planets of terrestrial group and analysis of cosmochemical consequences. In particular, authors discovered that temperature in the zone of formation of the Earth and Venus did not fall below 300-500 K, which preconditioned deoxidized, waterless state of a solid phase of substance in the given zone, different from the coaly chondrites (CI) for lack of hydrosilicates, volatile and organic compounds. They also established conditions of emergence of gravitational instability in the dust-gas subdisk and its disintegration in a zone of primary hoop compression into spherical dust concentrations of protoplanet dimensions of a weight of ~ 10²⁰-10²¹g.

Professors S.Valeyev, Yu.Nefediyev et al. considered the task of determination of relative position of lunar center of the masses and centre of the figure of the Moon. It is important both from the point of view of the origin, structure and evolution of the Earth's satellite, and from the point of view of the precise decision of the near-Moon navigation problems. The given task was solved by way of direct use of selenocentric catalogues of coordinates of objects in need of identification located more or less homogeneously on the entire surface of the Moon, as well as data of recent Moon-related missions. Initial coordinates of objects of the visible side of the Moon were taken from Kazan catalogue developed in the system of the center of the masses and main axes of inertia of the Moon. Transfer of the edge zone and the backside objects to the system of the given catalogue will allow for creation of a Uniform basic selenocentric system of lunar objects encompassing all explored by now sites on the surface of the Moon.

D.Titov's et. al report "Venus Express: three years of atmospheric observations" contained the detailed analysis of results of atmospheric research, examination of plasma environment and some data on geology of Venus obtained with the help of the European space vehicle. Russian scientists contributed to the project through the participation in creation of scientific equipment. The report contained characteristics of scientific instruments, received distributions of temperature and atmospheric pressure by altitude and latitude, spatial distribution of molecules of water and carbon dioxide. Non-equilibrium emissions of oxygen were detected, and global morphology of clouds and polar whirlwinds, as well as their atmospheric dynamics was studied.

Professor Z.Franck from Germany reported on "Gliese 581d: The first habitable super-Earth-planet". The report contained the analysis of factors necessary for the emergence of primitive forms of life on exoplanets, description of orbital zones of planets with favorable temperature and atmospheric conditions dependent on the weight of the central star. Presumably, one of the planets of the given system, Gliese 581d, discovered on April 24, 2007 possesses the necessary potential of habitability! The planet rotates around of the red dwarf Gliese 581 located at a distance of 20,5 light years from the Earth in Libra constellation. The discovery was made with the help of a 3,6 m telescope of the European southern observatory in Chile. The new planet is located close enough to the star - its orbital period is just 3,15 days. Thus, the heat on the surface of the planet excludes possibility of liquid water presence.

The session closed with A.Eremeyeva's report "Kazan origins of Schmidt's cosmogony and its consequences" containing the detailed review of the book about Schmidt's biography and his theory.

In the beginning of the next decade within the framework of the Russian program of complex lunar research "Luna-Glob" (2012) it is planned to launch the lunar probe intended for exploration of the internal structure of the Moon, to include, first of all, determination of thickness of the crust, borders in mantle, size and aggregate state of the core, and implementation of comprehensive surface studies by way of remote sensing and direct measurements. The given launch is to proclaim the "return of Russia to the Moon" and to open wide horizons of further research projects, such as "Luna-Resource" program with possible participation of India, which will include landing of moon rovers of new generation to obtain samples from the most interesting sites, which will be then delivered to the Earth by a returnable rocket, like it was the case with automatic spacecrafts "Luna-16, -20, -24". It should be emphasized, that it will be necessary to deliver several purposely collected samples from several geologically representative and most ancient formations of the Moon with a view of determination of the key characteristics of the earliest stage of the Moon's evolution, in particular, processes which led to formation of a continental crust. The program which has no analogues in the world is designed to answer most urgent questions about the nature and origin of the Moon and significantly contribute to the creation of permanent lunar bases by the year of 2025.