Prospects of research of lunar crust, mantle and core in 2010-2020

A.V.Gusev, Yu.A.Nefedyev

EAO, Kazan Federal University

Russia

We discuss geophysical parameters, geometrical and dynamic compression of liquid core and elastic mantel of the multilayered Moon. The research results include the survey of internal structure of the Moon, tabulated values of geophysical parameters and geophysical profile of the Moon, including liquid lunar core, analytical solution of Clairaut form for calculation of geometrical compression the two-layer model of the Moon; mathematical and bifurcational analysis of solution based on physically justified task options; original debugged software in VBA programming language for computer generated simulation for various intervals of radiuses, values of geometrical compression on the Moon surface, densities, as well as graphic representations of the received data. The given characteristics are important for the evaluation of free librations of the Moon layers – Chandler Wobble (CW), Free Core Nutation (FCN), Inner Core Wobble (ICW), Free Inner Core Nutation (FICN). Defined are horizons of research and development of the Moon for the nearest decade.

Most detailed map of the Moon South Pole to date has been recently published by NASA. New data have been collected by “Lunar Reconnaissance Orbiter” (LRO) robotic spacecraft which now orbits around the Earth natural satellite in a polar orbit (i.e. the orbit with the inclination angle of 90 degrees). LRO orbits at approximately 45 kilometers above the lunar surface – lower than all previous missions. Such low altitude and high quality of instruments ensured most detailed mapping of the polar region. In particular, LRO found traces of hydrogen at southern craters of the South Pole. The latter are in permanent shadow from the sun; therefore, many scientists consider the presence of hydrogen as a sign of water ice presence. According to recent data, temperature in these craters does not rise above approximately 33 K, so theoretically under the given conditions water can be kept for billions years. Within the framework of the project scientists studied craters surface with the help of Goldstone Solar System Radar transmitter located in California.

LRO has found the coldest site in the Solar system. It is located in the shaded craters near to the South Pole of the Moon. The coldest site has been identified in the course of mapping Moon surface temperatures. The temperature inside the craters reaches –240°C, which is just 33 degrees above the absolute zero. Even on Pluto which is 40 times farer from the Sun, the temperature is several degrees higher. Soon the temperature at the South Pole of the Moon will increase, and the coldest spot in Solar system will “move” to the North Pole. Cold craters may preserve most diverse molecules, such as water or methane. Apart from that, in the course of the study of chemical composition of molecules inside craters astronomers can obtain new information about early stages of formation of the Solar system. It is worth to note that lunar craters are the coldest natural sites of the Solar system.

More detailed information about the Moon geology would be very useful for the development of the lunar settlement project. Among other things, experts are interested in the availability of water. Delivery of cargoes to the Moon is extremely costly enterprise, whereas lunar base inhabitants would definitely need it, although none has been definitely detected so far. Lunar soil samples delivered to Earth by American and Russian explorers lack any traces of water. Many experts assumed that water ice can be found in always shaded craters muzzles.

NASA moon-crater-blasting Lunar CRater Observation and Sensing Satellite (LCROSS) mission in the beginning of October 2009 punched a hole in the lunar landscape and obtained evidence of presence of significant amount of water! First the upper stage of a booster rocket Centaur hit Cabeus crater located near the South Pole of the Moon at a speed of about 2,5 kilometers per second and created a plume of material from the bottom of the crater. The height of the dust pillar made nine kilometers. Then the structure of the dust has been investigated by various methods by the explorer which fell on the surface of the Moon three minutes later, as well as by other spacecrafts. LCROSS was necessary to put to rest the question of whether lunar poles have ice. It also collected information about mineralogical structure of the Moon surface, in particular, at ever-shaded sites. Stocks of water on the Moon will considerably facilitate the work of future manned lunar bases on the surface of the Moon, as glaciers can considerably reduce the cost of delivery of drinking and technical water from Earth.

Numerous space agencies and countries announced of plans for development of the Moon in the coming-up years. The main purpose is preparation and installment of long-term scientific-technical and research-industrial bases on the visible side of the Moon and next to lunar poles with a view of implementation of research experiments and development of lunar subsoil riches.

LRO and LCROSS (NASA) were the first large-scale missions of NASA within the framework of the lunar program “Constellation”. LRO was used by scientists for exploration of the Moon natural resources, mapping of radioactivity on its surface, and testing new technologies. According to the adopted program, the epoch-making event – lunar landing of USA citizens – should take place no later than in 2020.

Future research by the Japanese mission SELENE-2 of rotation and gravitational field of the Moon will include observation of physical libration of the Moon with the help of a telescope to be installed on one of the Moon poles in 2014 (ILOM project). 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 both core and mantle.

China second lunar probe, Change-2, will be launched in October 2010. Change-2 has undergone essential improvements, therefore it can be registered with the next generation of lunar probes: it will be equipped with high-resolution digital camera. In 2013 Change-3, first Chinese moon rover, will be launched to the Moon to search for mineral resources. At present engineers test the impellent system of the rover. First lunar landing of taikonauts is planned for 2020, whereas installation of a lunar base is planned for 2030. The latter will be then used as a launch center for launching Chinese piloted space vehicles to other planets, first of all, to Mars (provisionally in 2050).

LLR and radio-interferometry prospects within the framework of international cooperation of space powers in the field of observations, processing and interpretation of data urge for adequate theoretical developments necessary to create ranging technologies allowing measuring Earth-to-Moon distance with the accuracy of up to 1 mm. Kazan school of physical libration of the Moon can make significant contribution to that end. The 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 core and a viscous-elastic mantle. Realization of research-technical project “Space Nano Astronometry” (2010–2015) at Kazan State University on the basis of astronomical observatory named after V.P.Engelgardt will become a key element in Russia in terms of achievement of the targeted accuracy in the system of international observations of the Moon.

In the beginning of the next decade within the framework of the Russian program “Luna-Glob” (2012) it is planned to launch the lunar probe intended for exploration of the internal structure of the Moon, to include 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 sounding 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 the work of moon rovers of new generation in order to obtain samples from the most interesting sites, which will be then delivered to the Earth by a returnable rocket. 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 2025.

As a first attempt at solving the problem, the paper presents the survey of internal structure of the Moon, tabulated values of geophysical parameters and geophysical profile of the Moon, including liquid lunar core, analytical solution of Clairaut equation for the two-layer model of the Moon; mathematical and bifurcational analysis of solution based on physically justified task options; original debugged software in VBA programming language for computer generated simulation for various intervals of radiuses, values of geometrical compression on the Moon surface, densities, as well as graphic representations of the received data. Description of the geophysical profile of the Moon is based on exact mass, radius and moment of inertia of the Moon.