Scientists are still attracted by the Orb of Night. It is proved by the flight of the American LRO (lunar reconnaissance orbiter), equipped with the Russian LEND (lunar exploration neutron detector).

Cooperation of Russian and American* scientists is intended to solve a series of practical tasks to ensure further development of the Moon: to explore optimal landing areas for automatic and pilot-controlled vehicles; to conduct mineral exploration of lunar depths; to study the local radiological environment from the viewpoint of its impact on human health. But the main task is to find out if polar craters of the natural satellite of the Earth are surrounded by ice sediments, as some specialists, including Russian scientists, have predicted. The answer to this question will greatly influence a future program for the exploration of the Moon and the Solar System in general.

It is not difficult to understand why scientists are searching for water on the Moon. In future it will become a base for human activities in the Universe. It is there that experts are planning to build first extraterrestrial stations. Of course, researchers will need water and its components: oxygen (O) to ensure vital activities of astronauts and spacemen, and hydrogen (H) to produce rocket propellant. In other words, if water is found there, it will be of great help for the Moon's colonization!

Besides, there may be a lot of resources containing rare elements and minerals on the Moon. It is beyond doubt that the primary ore will be first thoroughly processed, and the obtained product will be many times less than the primary material. Moreover, no one is going to take a dead rock from there. But it may become expedient at the minimum to get some substances with a great consumption of energy on the satellite's surface in order not to contaminate the Earth and not to spoil its ecology.

In addition, in time the Moon is planned to be used as a kind of trans-shipping point or as an intermediate cosmodrome to launch rockets to the Mars and other planets of the Solar System.

Of course, not all specialists support these plans of the use of the Earth's satellite: they will bring a lot of problems due to contamination of our stratosphere and upper layers of the atmosphere with discharge products of powerful rockets plying to the Moon and back. But if a part of plans to colonize the Moon is realized in practice, water will become one of the key elements in their implementation.

The search for water will be conducted by the American LRO equipped with the Russian LEND, manufactured and financed by Roscosmos. This device was designed by the RAS Institute of Space Research (ISR), specialists of the Joint Institute for Nuclear Research (Dubna, Moscow Region) and the State Institute of Astronomy named after P. Sternberg, Moscow State University. The research supervisor of the project Igor Mitrofanov, Dr. Sc. (Phys. & Math.), RAS Institute of Space Research, is a member of the international scientific group in charge of operation of the LRO scientific and measuring complex.

The LEND is an improved version of the Russian neutron detector H END**, that helps the American space vehicle "Odysseus" to search for water on the surface of Mars***. By the present time, it has been working on the orbits of the Red Planet much longer than any other research equipment sent there for the whole period of its studies.

The LEND is designed on the principle of registration of secondary neutrons, which appear in the near-surface ground layer, 1-2 mm thick, under the influence of cosmic rays. They are partially absorbed and slowed down by the nuclei of the main rock-forming substances. An outgoing flow of these electric uncharged elementary particles depends on their composition and, first of all,

* See: Yu.  Markov,  "Russia-USA:  Space Cooperation", Science in Russia, No. 3. 2008.—Ed.

** See: "Neutron Spectroscopy of the Moon". Science in Russia, No. 5, 2009.--Ed.

*** See: I. Mitrofanov, "Unlocking Martian Enigmas", Science in Russia, No. 6, 2002--Ed.

on the presence of hydrogen and hydrogenous compounds. Measurement of absorption processes enables neutron detectors to determine changes of the hydrogen content in the near-surface layer right from the orbit. Since hydrogen is one of the two basic elements of water, it is possible to assess its volume in the soil.

The LEND installed on the LRO started functioning on July 19, 2009. It was put into operation a day after the launch of the American satellite to the Moon. In addition, scientists carried out studies of the Moon, making use of unique characteristics of the LRO orbit: for a period of two months its perihelion point (point of maximum proximity to the Moon) was located over its South Pole at an altitude of around 30 km. The result was a discovery of local areas characterized by low-level neutron radiation, which likely means a high hydrogen content. It has also been proved that these areas do not coincide with the formerly known shaded areas on the bottom of lunar craters. It was a surprise for scientists believed that these areas characterized by a high hydrogen content should coincide with eternally shaded areas in the environs of its poles. Thus, the first data obtained by the LEND refuted the generally accepted hypothesis on the location of areas with a high hydrogen content on the Moon.

According to the data received by the Russian device, the environs of the southern polar crater Cabeus holds the first place as for the hydrogen content in the soil. That is why it was selected by the LCROSS project scientific group and NASA as the place of a deliberate crash of space vehicles into the lunar surface. Why is the upper soil layer of the Cabeus crater and of other similar areas characterized by a high hydrogen content, and in what form does it exist (for example, implanted protons of the solar wind, water ice, hydrated lunar minerals)-all these questions are still open.

Much will become clear after the lunar bombing on October 9, 2009, when the American LCROSS probe cut into the big crater Cabeus. Analysis of the formed soil outcroppings will perhaps enable scientists to determine if there is a water ice on the Moon and to develop a new hypothesis that will explain the origin of local high hydrogen content areas discovered by the LEND.

Report of the ISR RAS Press Service

Prepared by Yaroslav RENKAS