Microsymposium 36, MS053, 2002

PERMANENTLY SHADED AREAS AT THE LUNAR POLES DURING THE PERIOD OF REGRESSIONOF THE LINE OF NODES. E. A. Kozlova, V. V. Shevchenko, Sternberg State Astronomical Institute, 119899,Moscow, Russia.

The orbit of the Moon is very nearly circular(eccentricity ~ 0.05) with a mean separation from theEarth of about 384,000 km, which is about 60 Earthradii. The plane of the orbit is tilted about 5,13° degreeswith respect to the ecliptic plane. The Moon's rotationaxis is not fixed in space. The regression of the line ofnodes of the Moon’s orbit has amplitude of 9” inobliquity and varies over a period of 18,6 years [1]. Themaximum altitude of the Sun above the celestialequator at midday is 1,53 °. So, the high of the limb ofthe Sun above the horizon is given by β = 90°- ϕ + 1,53° + δ

There ϕ - is latitude of the crater, δ =0,25°- is thehalf of visual diameter of the Sun.

Taking account of these movements, only centralpart of fresh deepest craters near poles might lie inconstant shadow during the all period of regression ofthe line of nodes of the Moon’s orbit. Water icedeposits can preserve in such craters. We used the frustum of cone model for largecraters with diameter larger than 10 km (see the fig. 1).Geometrical parameters characterizing our model arethe diameter of crater D, the depth of crater h, the floordiameter d and the wall slope α. Parameters have beenstudied in [2] according the size and degree ofdegradation of crater. Positive direction of X- axis isthe direction of lunar equator, S- axis is the direction ofthe center of the Sun, and Z- axis is the normaldirection of lunar surface.

Figure 1. The permanently shaded areas for lunar summermarked in blue and for the all period of regression of the lineof nodes of the Moon’s orbit marked in black.

We researched the regions with latitude higher than60° for both hemispheres of the Moon. 950 craters and1127 craters with diameters larger than 10 km wereconsidered for North and South Polar regions,respectively [3]. The areas, permanently shaded duringthe all period of regression of the line of nodes of theMoon’s orbit Sp, exist in 88 craters in the North Poleregion, and in 103 craters in the South Pole region. Theareas of these terrains are 0,0089% and 0,0131% oftotal lunar surface, respectively. We have investigatedthe craters according to area of permanently shaded

regions. Our estimates of the percentage of Sp arelisted in Table 1:

Table 1.The areas of permanently shaded regions for bothhemispheres of the Moon.

Sp N, km2 S, km2% totallunar

surfaceSp>100 km2 1955,57 3315,27 0,0139100km2>Sp>50km2

596,31 707,19 0,0035

50km2>Sp>20 km2 597,72 643,58 0,003320 km2>Sp>10km2

93,04 141,78 0,0006

10 km2>Sp>0 139,01 180,23 0,0009Sum 3381,65 4988,05 0,022

Some papers [4,5] had shown that effect ofsignificant portion of the enhanced hydrogen near bothpoles is corresponding to water ice deposits. Thedistributions of the Sp >10 km2 are shown at the fig 2.and fig.3. The crater Peary in North Polar Region isdemonstrating the enhanced hydrogen (H), especially insoutheastern corner. According to our calculations, thePeary is not contains the Sp areas. But two small craters(d = 10 km) are lie in southeastern part of Pearybottom. These craters are contains the permanentlyshaded areas Sp > 20 km2 and can contains water icedeposits. The much concentrations of hydrogen areoverlain a few small craters (D< 30 km) near the NorthPole. Our estimates of permanently shaded areas inthese craters is Sp >50 km2 (fig. 2). The maximumenhanced hydrogen near North Pole is overlain theheavily cratered region near the craterRozhdestvenskiy. There is no craters with diameter D >10 km, but there is many small, isolated craters, whichcan contains water ice.

H is enhanced in several craters (50 km>D>10 km)near the South Pole. These craters are contains thepermanently shaded areas Sp > 50 km2 and can containswater ice deposits. The largest concentrations ofhydrogen near the South Pole are overlay the cratersFaustini, Cabeus and unnamed crater at (87,20 S, 358,90

E), which contains the Sp > 100 km2 (fig. 3).So, the largest concentrations of hydrogen are

coinciding with areas, permanently shaded during theperiod of 18,6 years.

The paper is fulfilled with the support of INTASGrant No. 01-00792.

PERMANENTLY SHADED AREAS AT THE LUNAR POLES. V. V. Shevchenko

References: [1] Kulikov K.A. et al. (1972) Osnovylunnoy astrometrii.”Nauka”. [2] Rodionova J.F. etal.,(1988) An essential morphometric characteristics oflunar cratres.,Trudy Gosudarstvennogo Astro-nomicheskogo Instituta im. P. K. Shternberga, Tom LX,

p.179-183. [3] Rodionova J.F. et al.,(1987)Morfologicheskiy katalog kraterov Luny, ed MoscowUniversity, 177p. [4] Feldman W.C. et al., (1998)Science 281, p.1496-1500. [5] Feldman W.C. et al.,(2001) JGR.

Figure 2. The distributionof the permanently shadedregions Sp > 10 km2 at theNorth Pole of the Moonaccordingly the areas.Such regions are lies inthe small fresh craters orin the craters, lies on thebottom of large deepcraters. The zone wherewater ice can preserve isaround 15° the North Pole.

Figure 3. The distributionof the permanently shadedregions Sp > 10 km2 at theSouth Pole of the Moonaccordingly the areas. Thewater ice deposits canexist in some large (D>20km) craters near the SouthPole. The maximumpermanently shaded areais in the latitudinal zone85°-90°.