Microsymposium 36, MS087, 2002 PERMANENTLY SHADED AREAS AT THE LUNAR POLES DURING THE PERIOD OF REGRESSION OF THE LINE OF NODES V. V. Shevchenko 1 , E. A. Kozlova 1 . 1.Sternberg State Astronomical Institute, 119899, Moscow, Russia. The orbit of the Moon is very nearly circular (eccentricity ~ 0.05) with a mean separation from the Earth of about 384,000 km, which is about 60 Earth radii. The plane of the orbit is tilted about 5,13° degrees with respect to the ecliptic plane. The Moon's rotation axis is not fixed in space. The regression of the line of nodes of the Moon’s orbit has amplitude of 9” in obliquity and varies over a period of 18,6 years [1]. The maximum altitude of the Sun above the celestial equator at midday is 1,53 °. So, the high of the limb of the Sun above the horizon is given by β = 90°- ϕ + 1,53° + δ There ϕ - is latitude of the crater, δ =0,25°- is the half of visual diameter of the Sun. Taking account of these movements, only central part of fresh deepest craters near poles might lie in constant shadow during the all period of regression of the line of nodes of the Moon’s orbit. Water ice deposits can preserve in such craters. We used the frustum of cone model for large craters with diameter larger than 10 km (see the fig. 1). Geometrical parameters characterizing our model are the diameter of crater D, the depth of crater h, the floor diameter d and the wall slope α. Parameters have been studied in [2] according the size and degree of degradation of crater. Positive direction of X- axis is the direction of lunar equator, S- axis is the direction of the center of the Sun, and Z- axis is the normal direction of lunar surface. Figure 1. The permanently shaded areas for lunar summer marked in blue and for the all period of regression of the line of nodes of the Moon’s orbit marked in black. We researched the regions with latitude higher than 60° for both hemispheres of the Moon. 950 craters and 1127 craters with diameters larger than 10 km were considered for North and South Polar regions, respectively [3]. The areas, permanently shaded during the all period of regression of the line of nodes of the Moon’s orbit Sp, exist in 88 craters in the North Pole region, and in 103 craters in the South Pole region. The areas of these terrains are 0,0089% and 0,0131% of total lunar surface, respectively. We have investigated the craters according to area of permanently shaded regions. Our estimates of the percentage of Sp listed in Table 1: Table 1.The areas of permanently shaded regions for both hemispheres of the Moon. Sp N, km 2 S, km 2 % total lunar surface Sp>100 km 2 1955,57 3315,27 0,0139 100km 2 >Sp>50 km 2 596,31 707,19 0,0035 50km 2 >Sp>20 km 2 597,72 643,58 0,0033 20 km 2 >Sp>10 km 2 93,04 141,78 0,0006 10 km 2 >Sp>0 139,01 180,23 0,0009 Sum 3381,65 4988,05 0,022 Some papers [4,5] had shown that effect of significant portion of the enhanced hydrogen near both poles is corresponding to water ice deposits. The distributions of the Sp >10 km 2 are shown at the fig 2. and fig.3. The crater Peary in North Polar Region is demonstrating the enhanced hydrogen (H), especially in southeastern corner. According to our calculations, the Peary is not contains the Sp areas. But two small craters (d = 10 km) are lie in southeastern part of Peary bottom. These craters are contains the permanently shaded areas Sp > 20 km 2 and can contains water ice deposits. The much concentrations of hydrogen are overlain a few small craters (D< 30 km) near the North Pole. Our estimates of permanently shaded areas in these craters is Sp >50 km 2 (fig. 2). The maximum enhanced hydrogen near North Pole is overlain the heavily cratered region near the crater Rozhdestvenskiy. There is no craters with diameter D > 10 km, but there is many small, isolated craters, which can contains water ice. H is enhanced in several craters (50 km>D>10 km) near the South Pole. These craters are contains the permanently shaded areas Sp > 50 km 2 and can contains water ice deposits. The largest concentrations of hydrogen near the South Pole are overlay the craters Faustini, Cabeus and unnamed crater at (87,2 0 S, 358,9 0 E), which contains the Sp > 100 km 2 (fig. 3). So, the largest concentrations of hydrogen are coinciding with areas, permanently shaded during the period of 18,6 years. References: [1] Kulikov K.A. et al. (1972) Osnovy lunnoy astrometrii.”Nauka”. [2] Rodionova J.F. et al.,(1988) An essential morphometric characteristics of