Investigation and exploration of the Moon:

fundamental problems, international perspectives

б.V.Gusev, N.K.Petrova

Kazan State University

Kremlin st., 18, Kazan, 420008, Russia

N.лБwano

National Astronomical Observatory

Japan

At the present days, the Moon has become a target of several space missions, it is a focus of attention for researchers in Astronomy and Planetology. The main scientific objectives of Japanese-Russian Lunar Cooperation are oriented on the main purpose of planned Japanese Lunar Missions SELENE: RISE, ILOM - to investigate and describe particularities of orbital-rotational and inner dynamics of Moon as composite deformable celestial body, to suggest more effective model, analytical description, numerical approach and programs for lunar mission for more exact and effective determinations of gravitational field parameters, parameters of resonant Moon librations, parameters of its inner and surface structure. More exact data about gravitational field, figure, and physical fields will be obtained from this mission and will give new possibility for further dynamical studies. The Russian scientific project "The Moon-2012+"is directed on the solution of fundamental problems of celestial mechanics, selenodesy and geophysics of the Moon - that is connected with pursuance of theoretical researches and computer's modeling on the following fields. The project will provide the development of the theory of the libration of the Moon, improvement of values of a core's radius, of lunar elastic characteristics, of initial conditions of the rotation, the theoretical estimations of tidal variations of the selenopotential and figure of the Moon.

Lunar rotation (Physical libration - LPhL), construction of various models of lunar interior are included in the program of many planned space experiments. As a result, a hypothesis about the origin of the Earth-Moon system and about its evolution will be clarified. To the present time many interesting data concerning the dynamics and interior of the Moon are already accumulated. These data are obtained as result of various observations and of space experiments such as the ground based optical and satellite observations, seismic and magnetometer measurements during the programs Apollo and Lunokhod, space mission Clementine (1994) Й Lunar Prospector (1998-1999), European lunar satellite SMART-1 (2003 -2006), the Lunar laser ranging (LLR) performed during 40 years gave the phenomenal accuracy in determination of lunar parameters. The Japan space experiment SELENE, whose start is planned onto 2007, its first project RISE and second project ILOM (2012), and also the series of lunar space projects of other countries- CHANG'E-1 (China, 2007), LRO (NASA, 2008), Chandrayaan-1 (India, 2008), Luna Glob (Russia, 2012) - all these will essentially enrich our knowledge about the Moon and will open new prospects in development of nearest space.

The last discoveries require taking a new view of the evolution of the Moon, its origin and thermal history, to develop the experimental and theoretical investigations of our satellite.

1. Results of the modern space experiments are presented in the light of internal structure of the Moon. Practically all these data and also the modern theories of heat evolution of our satellite give evidences that the Moon has a little (no more 400-500 km) core. The FCN detection of the Moon and its period will allow:љ a) to decide on the physical nature of the lunar core - it is possible only for the liquid core; b) to determine core radius and its flattening; c) to determine density jump at the CMB and CMB flattening.

2. The models of formation of the lunar core are consistent with a variety of scenarios.љ For pure compositions (Fe or FeS, small or large core radii) an entirely solid core is likely, the mean composition of the core is close to the eutectic composition (20-25% S). In this case even an entirely liquid core seems possible due to the very low eutectic temperature.

3. Of great importance for core parameters refinement is the determination of physical libration parameters - libration angles, dissipative Love number k₂ and qualitative parameter Q - in various experiments. An LLR analysis has already contributed essentially in this problem solution. The construction of the high precision theory of libration is required to adequate performing of these observations is required.љ

4. Having the high-accuracy theory and observations, it is possible to include the searching for the new frequencies in libration series - FCN, FICN and ICW in the program of the future Japanese geodesy experiment SELENE II (ILOM project), which will provide the direct determination of the Moon orientation in space.

5. Our present research predict possible values of the periods of these new mode for the different model of lunar core (two-layer or three-layer model, dissipation model) and with various set of parameters: core radiuses, thick of FOC and density for different states of aggregation.

6. Results of the seismic observations by Japanese mission SELENE are expected to provide key data on the size of the lunar core and its physical properties. In the perspective of the planned space experiment SELENE observable data constraining the core parameters are considered: these are the moments inertia relation, Love number k₂.

7. The heat flow measurements will also provide important data on thermal structure and concentrations of heat-generating elements in the Moon. These data will help to test our hypothesis about the origin of mascons discovered by Clementine in the thick continental crust of lunar far side.љ We propose to develop the theory of physical libration through consideration of visco-elastic proprieties of lunar body and core mantle differential rotation to adequately describe the observational data in the frame RISE project.

8. The analysis of modern observations of Moon and the modeling of lunar rotation give grounds to suppose that at center of the Moon a small (from 200 up to 600 km) liquid iron-containing core is present. In proposal of the two-layer model of the Moon containing a rigid mantle and a elliptical liquid core the new mode, called the Free Core Nutation, should appear in the polar rotation of the Moon.љ Theoretical modeling of rotation leads to determination of the FCN period magnitude. Its value is slightly changed (no more than 1%) in dependence on the core radius.љ Detection of the FCN period in the lunar rotation will permit to answer on the question about existence of the lunar core and of its nature.

9. The models of convection evolution of the Moon, calculated before, predict the appearance of several plumes of various intensity and location. One of the additional heating of the planet's interiors may be the dissipative energy at CMB, converted in heat. It creates instable thermal layer leading of the upwelling mantle plumes. Top of the plumes in early Moon were conserved in form of mascons in the lunar continental crust, and as result the specific surface characteristics should be observed: 1) the pluton-like intrusions ("mascons"), 2) specific fluctuations of thermal ("warm spot"), gravitational fields, 3) the Mocho uplifts, topographic features in the form of arched lineament.

10. The large prospects in the decision of this problem are opened by the RISE and ILOM projects of SELENE-mission. Obtained data will allow to improve the physical libration theory of the Moon, and on the other hand, together with theoretical and observational libration data they will provide a further study of the lunar interior and, as a consequence, of its origin and evolution. Results of global topographic cartography set new problems and developed new opportunities to studying the lunar interiors. The heat history of the lunar evolution could make marks on the lunar surface as the traces of ancient plumes.