ISSN 00380946, Solar System Research, 2015, Vol. 49, No. 6, pp. 367–382. © Pleiades Publishing, Inc., 2015. Original Russian Text © M.A. Ivanov, A.T. Basilevsky, A.M. Abdrakhimov, I.P. Karachevtseva, A.A. Kokhanov, J.W. Head, 2015, published in Astronomicheskii Vestnik, 2015, Vol. 49, No. 6, pp. 403–419.
Crater Boguslawsky on the Moon: Geological Structure and an Estimate of the Degree of Rockiness of the Floor M. A. Ivanova, b, c, A. T. Basilevskya, b, c, A. M. Abdrakhimova, I. P. Karachevtsevab, A. A. Kokhanovb, and J. W. Headc a
Vernadsky Institute of Geochemistry and Analytical Chemistry (GEOKHI), Russian Academy of Sciences, ul. Kosygina 19, Moscow, 119991 Russia b Moscow State University of Geodesy and Cartography (MIIGAiK), Gorokhovskii per. 4, Moscow, 103064 Russia c Brown University, Providence, RI 02912, USA email: mishaivn@mtunet.ru,
[email protected] Received March 30, 2015
Abstract—The paper considers the results of a study of the geological structure of the floor of the crater Boguslawsky selected as a primary target for the LunaGlob mission. The deplanate floor of the crater is cov ered by the material ejected from remote craters and the crater BoguslawskyD on the eastern inner slope of the crater Boguslawsky. It is highly probable that the sampling of the crater BoguslawskyD ejecta will provide the unique possibility to detect and analyze the material that predates the formation of the largest and most ancient currently known basin on the Moon—the South Pole–Aitken basin. The rockiness degree of the Boguslawsky crater floor has been estimated from the radar data and the manual boulder counts in the super resolution images (0.5 m/pixel obtained with the Narrow Angle Camera from the Lunar Reconnaissance Orbiter). Comparison of the radar data to the results of the photogeological analysis shows that the main con tributor to the radar signal is the rock debris located in the subsurface layer sounded by radar (1–1.5 m), while there are practically no boulders on the surface. The two most rocky regions on the crater Boguslawsky floor are associated with the relatively fresh impact craters 300–400 m in diameter. The spatial density of boulders near the craters suggests that one of them is 30–50 Myr older than the other. For both of these craters, the spatial density of boulders drops with the distance from their rims. The rate of the decrease in the boulder spa tial density is the same for both craters, which points to the constantintime intensity of the fragmentation of boulders. The size distribution of boulders versus the distance from a rim of the older crater is approximated by the curve with a slope of –0.02, while the curve slope for the younger crater is –0.05. The gentler curve slope for the older crater is obviously connected with the equalization of sizes of the rock debris with time. The sizefrequency distribution of all rock fragments for the both craters, regardless of the distance from the rim, shows that mainly large boulders first crumble away as the surface age increases. Some large boulders near the young crater demonstrate the traces of rolling, while such traces are absent for the boulders near the older crater. This allows us to estimate the intensity of the reworking of a thin surface layer at 0.01 m/Myr. Keywords: Moon, LunaGlob mission, crater Boguslawsky, sizefrequency distribution of boulders DOI: 10.1134/S0038094615060039
INTRODUCTION The LunaGlob mission of the Russian Space Council (http://www.lg.cosmos.ru) is to land a probe on the lunar surface near the southern pole. Among the scientific objectives of the mission is the study of the physical state and chemical and mineralogical composition of the regolith in the nearpole region of the Moon. To complete these tasks, the onboard set of instruments includes the neutron and gammaspec trometers, mass and IRspectrometers, and TV cam eras of high resolution (http://www.lg.cosmos.ru/ devices). One of the engineering challenges of the mis sion is to test the safe landing technique in the rugged topography terrain abounding in longterm and per petually shadowed regions.
The ballistic limitations of the LunaGlob mission allow the landing in the southern polar sector with the coordinates between 70°–85° S and 0°–60° E. In this area, the potential landing sites should be within the landing ellipses of 15 × 30 km each. In these ellipses the surface should be as smooth as possible (the mean slopes should be less than 7° at the 50m baseline), and no large boulders should be there if possible (the boul ders of 30–50 cm and larger pose a serious threat to the lander). From the preliminary geological analysis of the landing sector, several potential landing sites were selected (Ivanov et al., 2014). These regions are char acterized by both the smoothed surface and the low ered epithermal neutron emission, which indicates the
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Fig. 1. Topographic map of the southern polar region of the Moon (the data of the LOLA altimeter onboard the LRO spacecraft; the resolution is 64 pixel/degree), where the location of the crater Boguslawsky is indicated. The rims of some large impact craters are contoured with thin dashes. The approximate location of a part of the rim of the South Pole–Aitken basin is shown with a thick dashed line. A black frame indicates the landing sector of the LunaGlob mission.
increased content of hydrogen in the regolith (Boyn ton et al., 2012; Mitrofanov et al., 2012). Later, for the reasons of safety of the mission, the area of potential landing sites was narrowed; and the crater Boguslaw sky floor was finally selected for the landing. This crater, approximately 100 km in diameter, is at 72.8° S, 43.2° E within the ancient cratered terrain (Fig. 1). The crater’s floor is about 55–60 km across, and it is a morphologically smooth, flat, horizontal plain. Two landing ellipses were selected on its surface; their centers are at 72.9° S, 41.3° E (the western one) and 73.9° S, 43.9° E (the eastern one). The crater’s floor is not a region of a noticeably reduced emission of epithermal neutrons (Mitrofanov et al., 2012), which points to the relatively low hydro gen content in the regolith that is close to its back ground level in the southern nearpole region, 0.1– 0.2 wt % (Feldman et al., 2000; 2001; Mitrofanov et al., 2012). In spite of the absence of an expressed neutron anomaly, the crater Boguslawsky is a forma tion that is important for solving the other fundamen tal problems of the study of the Moon. The point is that the crater is located on the rim of the largest and, probably, oldest basin among the currently known lunar formations—the South Pole–Aitken (SPA) basin (Wilhelms et al., 1979; StuartAlexander, 1978; Wilhelms, 1987; Spudis et al., 1994; Hiesinger and
Head, 2004; Shevchenko et al., 2007; GarrickBethell and Zuber, 2009; Hiesinger et al., 2012). Such loca tion of the crater provides the unique possibility to examine the most ancient rocks on the Moon that probably predates the forming event of the SPA basin (4.2–4.3 Ga) and characterizes the initial stages of the geological evolution of the Moon. Due to the singular scientific importance of the challenges facing the LunaGlob mission, to provide its safety is of high priority. In this paper, we consider one of the safety aspects of the mission: the abun dance, geological associations, and sizefrequency distribution of boulders on the crater Boguslawsky floor and, specifically, within the selected landing ellipses. The photogeological studies of the crater allow one to specify the geological context of the future landing sites. The crater was analyzed with the images of the medium (100 m/pixel) and ultrahigh resolu tion (0.5–1 m/pixel) acquired with the Wide Angle Camera (WAC) and Narrow Angle Camera (NAC), respectively, onboard the Lunar Reconnaissance Orbiter (LRO). The new topographic data with a spa tial resolution of 30 m/pixel and the radar data with a spatial resolution of 150 m/pixel obtained from the Lunar Orbiter Laser Altimeter (LOLA) and MiniRF instrument, respectively, played an important role in SOLAR SYSTEM RESEARCH
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the study of the crater. Both these instruments are in the scientific payload of the LRO spacecraft. GEOLOGICAL STRUCTURE OF THE CRATER BOGUSLAWSKY FLOOR From the geological analysis of the crater Bogus lawsky, four morphologically different types of the ter rain were distinguished within its floor (Fig. 2): (1) rolling plains, (2) flat plains, (3) ejecta from the crater BoguslawskyD at the eastern slope of the host crater, and (4) clusters of secondary craters. Rolling Plains (rp) This unit is mostly observed near the northern and southern borders of the floor and in its central part (Fig. 2). Since the spatial location of the plains may be determined by their different nature, we divided the morphologically single unit of rolling plains to two categories: (a) rolling plains at the crater’s walls (rpw in Fig. 2) and (b) rolling plains in the center of the floor (rpc in Fig. 2). Rolling plains are characterized by the rugged relief formed by gentle swells up to several hundreds of meters high and a few kilometers across (Fig. 3a). The swells alternate with gentle curvilinear valleys of a few kilometers in length and width, and their crosssection is Ulike in shape. In some places of the surface of the plains, flatbottomed rounded depressions from hun dreds of meters to a few kilometers across are seen. The rolling plains within the flat floor of the crater Boguslawsky are topographically lower than the slope inflection separating the wall and the floor. The out crops of plains near the walls are bowshaped, which is determined by the shape of the crater, and extend to 30–35 km with a width of 5–10 km (Fig. 2). The roll ing plains in the central part of the floor form the elon gated fragments approximately 30 km long and 8– 10 km wide that extend from the northeast to the southwest (Fig. 2). Two remnants of the morphologi cally rolling plains are located in the southwestern part of the floor and completely surrounded by other mate rial units. The remnants were classified as rpc units (Fig. 2). The rolling plains occupy approximately 790 km2, which amounts to 29% of the floor area (Table 1). The chains of impact craters (probably, secondary craters) are seen in the rolling plains near the northern wall of the crater Boguslawsky (Fig. 3a). Some of these chains are localized within the boundaries of the plains and not observed in the adjacent types of the terrain, which suggests that the rolling plains are older. The absolute model age of the surface of the plains is esti mated from the sizefrequency distribution of the pri mary craters at approximately 3.96 Gyr (Hiesinger et al., 2014; Ivanov et al., 2015). This estimate cannot be distinguished from that for the age of the crater’s walls, which shows that the rolling plain is one of the most SOLAR SYSTEM RESEARCH
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Table 1. The area of stratigraphic units on the crater Bogus lawsky floor Area, percent of the floor
Unit
Area, km2
Secondary craters Ejecta from the crater Bo guslawskyD Flat plains Rolling plains, walls Rolling plains, center Total
289.2 837.5
10.8 31.5
753.4 523.5 264.8 2668.3
28.2 19.6 9.9 100.0
ancient material complexes on the floor of the crater Boguslawsky (Hiesinger et al., 2014), corresponding in age to a complex of ancient continental sheets Ntp (Wilhelms et al., 1979). Flat Plains (fp) Flat plains prevail in the western part of the floor (Fig. 2) and cover approximately 753 km2 or around 28% of its area (Table 1). The surface of the flat plains is complanate and subhorizontal (Fig. 3b). The ampli tude of their relief is approximately 100 m for the dis tance of 40–45 km. The main elements composing the plains are impact craters, and the largest of them (at the southern edge of the plains) reaches 3 km in diam eter. In the NAC highresolution images, it is seen that the contacts of the flat plains with the rolling ones and the swells are rather sharp, which is indicative of the underflooding of swells and rolling plains by the mate rial of the flat plains. The counting of impact craters on the surface of flat plains allows the age of this com plex to be estimated at 3.77 Gyr (Hiesinger et al., 2014; Ivanov et al., 2015), which corresponds to the Early Imbrian of the geologic history (Stöffler et al., 2006). Though the flat plains are younger than the rolling plains, there are noticeably more small (less than one hundred meters) impact craters on their sur face. This phenomenon is likely connected with the predominant destruction of small impact craters by the slope processes within rolling plains (Basilevsky, 1976). The spectral data of the Clementine spacecraft, that present the possibility to estimate the material compo sition of the surface, were acquired at large phase angles. Under such geometry of observations, the sur face albedo variations, that are the main source of information, are hardly distinguishable. Nevertheless, in the available spectral maps, the floor of the crater Boguslawsky cannot be visually distinguished from its walls and the terrain outside the crater. This suggests that both the rolling and flat plains are most likely rep resented by the material, whose composition is close to that of the surrounding highland terrain. In this case, the rolling plains near the crater’s wall may be
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Fig. 2. Geologic map of the crater Boguslawsky floor composed from the data of the WAC camera onboard the LRO spacecraft (the resolution is 100 m/pixel). White squares with numbers indicate the places, where the boulders on the surface were counted in the superresolution images (the NAC camera onboard the LRO spacecraft; the resolution is 0.5 m/pixel). Polar stereographic projection; the center of the image is at 73° S, 43° E.
Ejecta from the Crater BoguslawskyD (ejf)
unit that covers the whole eastern half of the floor (Fig. 2). The area of the ejf unit is approximately 837 km2 or 31% of the total area of the floor (Table 1). The surface of the unit (Fig. 3c) is gently undulating with numerous low (less than 100 m) flattopped hills and small flatfloor dishes; it looks less cratered than the adjacent flat or rolling plains.
Ejecta from the crater BoguslawskyD on the east ern wall of the host crater forms the blankets extending outside the crater Boguslawsky and covering its inner slope and floor. In our study, we considered only the ejecta portion that is on the floor. This portion of the ejecta blanket is the most widely spread stratigraphic
The ejecta is evidently the redeposited material of the eastern part of the crater Boguslawsky rim and rep resents the youngest unit on its floor. Such strati graphic location of the ejf unit agrees with the esti mates of its absolute model age, 3.74 Gyr (Hiesinger et al., 2014; Ivanov et al., 2015).
slump bodies, while the fragments of plains in the cen tral part of the floor are either the outcrops of the cen tral massif or the ejecta material from the nearby or remote craters. The flat plains can be either the impact melt or the crater ejecta.
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Fig. 3. The surface structure of the stratigraphic units (material complexes) mapped in the crater Boguslawsky floor. (a) The sur face of rolling plains near the crater’s walls (the rpw unit) in contact with the flat plains (the fp unit). Within the rolling plains, one may observe the chains of craters (marked by arrows) that are probably overlapped by the material of flat plains. A white solid curve indicates the contact of the rolling and flat plains. Mosaic of the WAC images with a resolution of 100 m/pixel. Polar stereographic projection; the center of the image is at 72.2° S, 42.8° E. (b) The surface of rolling plains in the crater’s center (the rpc unit) sur rounded by flat plains. The contact of the units is indicated by a white solid curve. Mosaic of the WAC images with a resolution of 100 m/pixel. Polar stereographic projection; the center of the image is at 72.9° S, 41.7° E. (c) The surface of the blanket of ejecta from the crater BoguslawskyD. Mosaic of the WAC images with a resolution of 100 m/pixel. Polar stereographic projec tion; the center of the image is at 73.1° S, 44.2° E. (d) The cluster of secondary craters composed of small impact structures with diameters from tens to first hundreds of meters. The NAC narrowangle image (M144342979) with a resolution of 0.5 m/pixel. Polar stereographic projection; the center of the image is at 72.3° S, 45.1° E.
Clusters of Secondary Craters (sc) Clusters of secondary craters are observed in many places on the floor of the crater Boguslawsky (Fig. 2). They are compact, often elongated gatherings of cra ters with diameters from tens to a few hundreds of meters (Fig. 3d). However, in the northwestern part of the floor, there is a cluster containing the craters 1– 2 km in diameter. Inside the craters of the clusters shown in Fig. 3d, shadowed regions are seen. Conse quently, the steepness of the craters' walls is larger than the Sun elevation above the horizon, that is 13°–14° in the considered cases. Nevertheless, no rock debris is seen on the rims and walls of the secondary craters. SOLAR SYSTEM RESEARCH
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Thus, the clusters of secondary craters are not rocky terrains, though the values of slopes are high in these regions. This is probably connected with the enhanced efficiency of the slope processes that bury the coarse clastic material under the finegrained regolith layer. A fraction of the clusters of secondary craters in the structure of the crater Boguslawsky floor is relatively small: their total area is approximately 289 km2 or 10.8% of the total area of the floor (Table 1). However, the clusters are not concentrated and occur in many places (Fig. 2). Since the orientation of the extension of the clusters are different, it can be definitely stated that they are associated with the ejecta from different craters located outside the crater Boguslawsky.
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THE NATURE OF MATERIAL BODIES ON THE CRATER BOGUSLAWSKY FLOOR A specific property of the crater Boguslawsky is that the ratio of its depth to the diameter d/D is relatively small. For this crater this morphologic parameter is approximately 0.038, while the value of the ratio d/D for the other large craters in the landing zone (Boiss ingault, Schomberger, Simpelius) ranges from 0.051 to 0.057. The deplanate shape of the crater suggests that it was filled with some material after formation. The slopes of the walls of the crater Boguslawsky cannot be distinguished from those of the other craters and do not exclude the leading part of the sliding processes in its filling, though the slump bodies are definitely observed inside the crater Boguslawsky. The other probable cause of the decreased depth of the crater— its volcanic flooding—is not confirmed by the spectral data. Thus, the most probable cause of a small value of d/D of the crater Boguslawsky is its infilling with ejecta from the neighboring or remote craters. To understand to processes that probably formed the material complexes on the floor of the crater, we consider a set of model geological crosssections directed from the west to the east. They illustrate three possible mechanisms of the infilling of the crater Boguslawsky. To build the crosssections, we used the current relief of the crater, and the altitude position of its pri mary floor was estimated by the typical value of the depthtodiameter ratio (d/D) for the craters of the same size category (Pike, 1977). The considered mod els mainly differ by the interpretation of the nature of rolling plains in the central part of the crater (Fig. 4). In the first of the considered crosssections, the unit of rolling plains is presented by outcrops of the central massif of the crater Boguslawsky (Fig. 4a). The flat plains may be either the volcanic flooding of the crater, which is hardly probable, or the impact ejecta. In the present model, the central massif looks dispro portionately wide and high (analogous formations in the craters of the same size are considerably smaller) and substantially shifted to the western wall of the cra ter. The other difficulty of the interpretation of the rolling plains as a central massif is connected with a strongly elongated shape of the outcrops of plains (Fig. 2). This poorly agrees with the typical configuration of such formations in the other lunar craters. Thus, it is hardly probable that the central region of the rolling plains is the outcrops of a central massif of the crater. In the second model, it is assumed that the crater Boguslawsky is mainly filled with ejecta from remote or neighboring large craters (e.g., ejecta from the cra ter Boussingault). In those places, where the ejecta drapes the central massif, the rugged relief of rolling plains appears (Fig. 4b). This model meets two main problems. First, this model, as the first one, does not explain the elongated shape of the central cluster of plains. Second, it fails to explain the sharp boundaries
between the rolling and flat plains. If the material of both these units were of approximately the same gran ulometric composition and their relief were deter mined by the presence or absence of an underlying massif, the gradual transitions from one type of the plains to another should be expected. In such a case, they would be the facial differences of the same material. Finally, in the third model, the rolling plains are coarse clastic fractions of ejecta (Fig. 4c). In this sce nario, the westward shift of the cluster of rolling plains and its elongated shape is not a problem. On the con trary, they are the consequence of the mechanism of the ejecta deposition; and the different morphology and sharp boundaries of the rolling and flat plains are explained by their granulometric composition and dif ferent time of deposition. The considered models of the infilling of the crater Boguslawsky determine the variety of types of the material that may be present on the crater’s floor. Though all of these models are probable to this or that extent, their common feature is the blanket of ejecta from the crater BoguslawskyD. This ejecta quite def initely originates from the local source (the rim of the host crater) and overlaps all previous material units (Fig. 4). In turn, the rim of the crater Boguslawsky is composed of the material that had been moved during the formation of the SPA impact basin; and, conse quently, it is more ancient than the basin. Thus, the ejecta from the crater BoguslawskyD should contain the rocks dating from the most ancient periods of the geological history of the Moon. These rocks are an objective of the highest scientific priority. How dan gerous or safe can be the landing on the ejecta blanket of the crater BoguslawskyD? To answer this question, the estimates of the spatial and sizefrequency distri bution of boulders may help. DATA SOURCES FOR DISTINGUISHING BOULDERS There are three data sources that make it possible to distinguish boulders on the surface and in the subsur face layer of the Moon. First, this is the imaging survey with an ultrahigh resolution by the LROC NAC cam era, which allows the details of several tens of centime ters across to be distinguished. The boulders larger than 1 m across, that really pose a threat to the lander, can be directly counted, and their position and sizes can be determined in the NAC images with the ArcGIS Crater Tools application (Kneissl et al., 2011). The NAC LROC images form a necessary basis for determining the spatial and sizefrequency distribu tion of boulders on the lunar surface. The second source is the radar data acquired with the radar onboard the LRO spacecraft (the MiniRF instrument) (Nozette et al., 2010). Though the spatial resolution of the MiniRF instrument is much worse (from 30 to 150 m/pixel) than that of the NAC data, SOLAR SYSTEM RESEARCH
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Fig. 4. A set of model geologic crosssections of the crater Boguslawsky from the west to the east. The vertical scale is fivefold. See the text for discussion.
the wavelength of the radar survey, 12.6 cm, makes it possible to notice the boulders with diameters of around 30 cm and larger. To estimate the number and abundance of boulders on the floor of the crater Boguslawsky from the radar data, we analyzed the variations of the values of the circular polarization ratio (CPR) of the radar signal. This quantity is a ratio of the power of the reflected sig nal polarized in the same direction as the sent beam to that polarized in the reverse direction (Spudis et al., 2009; 2010; Nozette et al., 2010). The CPR values are sensitive to the presence of either ice concretions or large boulders, or both types of these objects in the sounded layer (approximately ten wavelengths of the radar beam). The characteristic size of these fragments should be larger than several wavelengths (Campbell et al., 1978; Harmon et al., 1999; Black and Campbell, 2004; Spudis et al., 2010). The recently published maps of the neutron emission from the surface of the southern nearpole region of the Moon (Mitrofanov et al., 2012) show that the floor of the crater Boguslawsky is not a noticeable anomaly of the decreased neutron emission at all. Consequently, the crater can be con SOLAR SYSTEM RESEARCH
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sidered as a “dry” region, and the CPR variations on its floor are connected with the presence of boulders rather than ice. The boulders are both located on the surface and distributed in the subsurface layer of 1– 1.5 m thick (Neish et al., 2010). One more source of the data on the granulometric composition of the surface material that should be mentioned is the data of the DIVINER IR spectrom eter characterizing the diurnal behavior of the surface temperature (Paige et al., 2010). These data can be transformed into the thermal inertia model of the sur face, which may yield the estimates of the granulomet ric composition of its material. However, we do not here consider the data of the DIVINER instrument, since they have not been calibrated yet with respect to the number of rock fragments. INTERPRETATION OF THE RADAR DATA The map of the circular polarization ratio for the crater Boguslawsky floor (Fig. 5) shows that the CPR values are substantially smaller within the western ellipse than inside the eastern one. Such spatial distri
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Table 2. Comparison of the surface rockiness (direct counts from the superresolution images) and the values of the circular polarization ratio (CPR) for the crater Boguslawsky floor Count region of boulders
Total area, km2
1 2 3 4 5
4.15 5.56 5.48 2.36 3.26
Area Area with boulders, km2 with boulders, % 0.057 0.004 0.001 0.022 0.004
bution of the CPR values is apparently connected with the fact that the most abundant material in the eastern ellipse is represented by ejecta from the crater Bogus lawskyD. This unit is the youngest one from the stratigraphic point of view, and it probably contains a large portion of the largeboulder fraction. The radar survey clearly demonstrates the peculiar ities of the spatial distribution of boulders on the floor of the crater Boguslawsky (Fig. 5). Nevertheless, it gives us no indication of what portion of the reflected signal is connected with the boulders lying on the sur face and what portion is associated with the boulders distributed within the sounded layer. To estimate a portion of the signal connected with the boulders on the surface, we counted their number in five sites on the crater’s floor with the use of the NAC images with a spatial resolution of 0.5 m (Table 2, Fig. 2). The count regions of boulders were selected in such a way that the sites with the visually different and elevated values of CPR can be characterized; however, the regions with extremely high values of this parameter, for example, the crater’s walls, where the landing is impossible in any case, should be avoided. The CPR values in the selected regions vary from 0.38 to 0.65, which is generally higher than the mean value of this parameter for the crater Boguslawsky floor (0.39 ± 0.09). The comparison of the averaged values shows no correlation between these parameters (Fig. 6). For example, the region, where the spatial density of boulders is maximum (1.4%, region 1), is characterized by the averaged CPR of 0.47, while the spatial density of boulders in the region with the high est value of CPR (0.65) is only 0.12% (Fig. 6). No cor relation between the spatial density of boulders on the surface and the CPR values suggests that the main contributor to the radar signal is the rock debris located in the sounded subsurface layer. Such boulders pose no danger to the lander. Thus, the ejecta zone of the crater BoguslawskyD is not dangerous from the point of rock debris. Estimates of the variations of the surface slopes on the 30m baseline (Ivanov et al., 2015) also give us no grounds to consider the ejecta from the crater BoguslawskyD as a highrisk zone for the landing of the LunaGlob probe.
1.38 0.08 0.02 0.93 0.12
CPR, averaged
CPR, statistical deviation
0.469 0.483 0.468 0.375 0.645
0.142 0.045 0.064 0.038 0.116
SPATIAL AND SIZEFREQUENCY DISTRIBUTIONS OF BOULDERS Two of five regions, where the boulders were counted, (1 and 4 in Fig. 2) are associated with rela tively fresh craters of 300–400 m across that are sur rounded by many boulders. This allows us to quantita tively estimate the spatial and sizefrequency distribu tions of rocky fragments associated with the ejecta from small craters. Near crater 1 (73.0° S, 42.0° E; 419 m in diameter; Fig. 7a), in the circular area of 1347 m in diameter (approximately three diameters of the crater), 9351 rocky fragments from 1 to 13 m across were detected. The mean spatial density of boulders in this region is around 73 boulders per 10000 m2. Crater 1 is on the surface of the rpc unit (Fig. 2) that is apparently a largeboulder fraction of ejecta from the remote crater (Fig. 4). The boulders are spatially distributed along the rays that radiate from the crater’s center and are separated by the regions containing practically no boulders (Fig. 7a). The rays extend to many hundreds of meters, and their width near the crater’s rim is a few hundreds of meters. An important property of the sur face near crater 1 is that the traces of rolling of large boulders are seen behind some of them: they appear as shallow grooves approximately 30–50 cm deep (Fig. 7b). Around crater 4 (72.6° S, 44.9° E; 356 m in diame ter; Fig. 8), in the area of 1008 m in diameter (approx imately three diameters of the crater), 3959 rocky frag ments from 1 to 8 m across were detected. The mean spatial density of boulders in this region is around 41 boulders per 10 000 m2. Crater 4 is also located on the blanket of ejecta from the crater BoguslawskyD (Fig. 2). Thus, the nature of the targets of craters 1 and 4 is probably the same. The spatial distribution of boulders is the same as that around crater 1, though its ray structure is less expressed, the rays are narrower, the boulderfree spaces between them are wider (Fig. 8b). The rolling traces of boulders in the vicinity of crater 4 are not observed. It is evident that the number of boulders in the vicinity of the craters is connected with the age of impact structures: there are naturally more boulders around fresher craters than around older ones. The SOLAR SYSTEM RESEARCH
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375 N
w
ejf ejw
w 5 km
Fig. 5. The circular polarization ratio (CPR) for the crater Boguslawsky floor mapped from the MiniRF radar data of the LRO spacecraft. Bright and dark tones correspond to the high and low CPR values, respectively. In the right part of the figure, the boundary of the blanket of ejecta from the crater BoguslawskyD is contoured in white. The position of landing ellipses are shown by solid blackandwhite lines. Polar stereographic projection; the center of the image is at 73° S, 43° E.
recent studies on the survival time of boulders around the craters of the known age showed that the spatial density of boulders near their rims decreases with time according to the exponential law with the fixed param eters (Basilevsky et al., 2013). Thus, the results of the boulder counting quantitatively illustrate the aging process for craters and their ejecta on the lunar sur face. In this analysis, it is reasonably assumed that approximately the same number of boulders were ejected to the surface, when the craters of approxi mately the same size were formed in the targets of sim ilar nature (in this particular case, this is the ejecta from larger craters). More rock fragments around cra SOLAR SYSTEM RESEARCH
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ter 1 means that this crater was formed later than crater 4. The spatial density of boulders in the first two zones adjacent of the rims of the craters is 105 and 75 frag ments per 10000 m2, respectively, which is approxi mately 28% higher for crater 1 than for crater 4. According to the estimates of the survival time of boul ders on the lunar surface (Basilevsky et al., 2013), this difference in the spatial density of boulders means that crater 4 is 30–50 Myr older than crater 1. The abundance of boulders allows us to estimate some parameters of their spatial and sizefrequency distribution in the vicinity of impact structures. To obtain such estimates, we divided the count area of
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0.8
0.7
CPR value
Region 5 0.6
Region 1
Region 2
0.5
Region 3
0.4
Region 4 0.3 0
0.2
0.8 0.4 0.6 1.0 1.2 1.4 Area portion occupied by boulders, %
Fig. 6. Comparison of the averaged CPR values and the area portion occupied by rock fragments (larger than 1 m) on the surface in the count regions of boulders (see Fig. 1). No correlation between the compared parameters is evi dent. The vertical amplitude of the CPR values corre sponds to one standard deviation.
boulders (three diameters of the central crater) into ten zones with the same area that is approximately equal (93%) to the area of the central crater. In each of the zones, we calculated the spatial density of boulders and their sizes, which allows us to trace how these parameters change with the distance from the crater. When considering the variations in the spatial den sity of boulders, it is important to note that the curves of the density distribution of these two craters are practically parallel to each other (Fig. 9) and, conse quently, the process of degradation of boulders practi cally did not change with time. This result could be expected, since the determining role in the destruction of craters and their ejecta is played by a single factor, impact events, whose intensity has remained approxi mately constant after the epoch of intense meteoritic bombardment (Neukum et al., 2001). In the first two zones around the craters (1.7 diam eters of the central crater), the spatial density of boul ders quickly decreases. The slope of the density curve near the craters is –0.41 and –0.43 for crater 1 and 4, respectively (Fig. 9). Due to such a slope, the spatial density of boulders near crater 1 diminishes by approximately 26 and 40% in the second and third
zones, respectively, relative to the first one. For crater 4, the decrease of the density is sharper, and the spatial density of boulders diminishes by approximately 43 and 60% in the second and third zones, respectively, relative to the first one. Starting from the third zone (two diameters of the central crater), the spatial density of boulders decreases much slower. The slope of the curve of the density distribution amounts approximately –0.08 and –0.10 for crater 1 and 4, respectively (Fig. 9). Though the spatial densities of boulders near cra ters 1 and 4 change practically in the same way (Fig. 9), the sizefrequency distributions of boulders show a different pattern: the mean sizes of boulders in the zones around crater 1 decreases noticeably faster than those for crater 4 (the curve slopes are –0.05 and –0.02, respectively; Fig. 10). The gentler slope of the curve for the older crater 4 is obviously connected with the equalizing of sizes of rock fragments with time. This process most strongly manifests itself in the first two zones, where the largest fragments fall immedi ately after the impact event (Oberbeck, 1975). With the distance from the crater and with time, the size variations of boulders around the craters of different age are more and more smoothed over, and the curves of the size distributions of boulders converge (Fig. 10). The curves of the sizefrequency distribution of boulders observed in the vicinity of craters 1 and 4 (all zones, from the first to the tenth one included) are characterized by different slopes: –4.29 and –5.78 for the boulders around crater 1 and 4, respectively (Fig. 11). The difference in the slope of approximating curves shows that the larger boulders are destroyed faster (Hörz, et al., 1985). Otherwise, either the curves would be parallel to each other, if the destruction rate were the same in the whole size range, or the curve slope for the older crater 4 would be gentler, if smaller boulders were predominantly destroyed. If we assume that the sizefrequency distributions of boulders during the formation of craters 1 and 4 were the same, we may trace the dynamics of the destroying of boulders for the time period separating the craters, 30–50 Myr (Fig. 11; Table 3). It is seen from Table 3 that, during this time, approximately 50% of the boulder population in the size range from 2.8 to 4 m were destroyed, while this quantity is almost 90% for the range from 8 to 11 m. For the smaller boulders, the differences in the spatial density become smaller and amount from 30 to 40% for the diameter range from 1 to 2.8 m (Table 3). This is probably con nected, first of all, with the larger time required for destroying small boulders (Hörz, et al., 1985; Basi levsky et al., 2013) and, second, with the replenish
Fig. 7. (a) The vicinity of a younger crater 1 (73.0° S, 42.0° E), where the boulders larger than 1 m were counted. White concentric circles indicate the boundaries of the equalarea zones around the crater. The zones are numbered (numbers are in the bubbles). Each of the zones are approximately equal to the central crater by area. (b) The rolling traces of boulders near crater 1 appeared as shallow grooves (pointed by arrows). SOLAR SYSTEM RESEARCH
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Crater 1
100 m
(а) N
10 m
(b)
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Crater 4
100 m Fig. 8. The vicinity of an older crater 4 (72.6° S, 44.9° E), where the boulders larger than 1 m were counted. White concentric circles indicate the boundaries of the equalarea zones around the crater. The zones are numbered (numbers are in the bubbles). Each of the zones are approximately equal to the central crater by area.
ment of the population of small boulders at the expense of crumbling away the larger ones. The estimate of the age difference between craters 1 and 4 (30–50 Myr) allows us to get an idea of the intensity of the reworking of the lunar surface by small impact events. This characteristic can be derived from the fact that the traces of rolling are seen behind large boulders near crater 1, while there are no such traces near crater 4 (Fig. 7b). Consequently, for the time period between the impact events of two craters, the rolling traces of boulders were destroyed. The depth of the grooves left by boulders near crater 1 is approxi mately 30–50 cm. Thus, the regolith layer with a thickness of several tens of centimeters was reworked for 30–50 Myr, which yields the reworking rate of the upper layer of the lunar surface of approximately
0.01 m/Myr. In this case, by reworking is meant the grubbing and mixing of the layer of this thickness by meteoritic impacts rather than its removal (Basilevsky, 1974). This estimate practically coincides with that obtained from the analysis of the process of destruc tion of small (200–300 m) craters on the Moon (Fas sett and Thomson, 2014). These authors estimate the survival time of such craters at approximately 3 Myr, which yields the reworking rate of the lunar regolith layer with a thickness of several tens of meters also around 0.01 m/Myr. The closeness of these estimates suggests that the refreshing of the lunar surface at the expense of grub bing by impact events was going on with the same intensity in a wide range of the reworked layer thick nesses, differing by two orders of magnitude. SOLAR SYSTEM RESEARCH
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2.3
2.2 Crater 1
Mean boulder diameter, m
Spatial density of boulders, 10000 m–2
Crater 1
–0.41
100
Crater 1, mean: 73 boulders/10000 m2 –0.43
–0.08
50
Crater 4, meanе: 73 boulders/10000 m2 Crater 4
–0.10
2.1 –0.05
2.0 –0.02
Crater 4
1.9
1.8
0
1.7 1
2
3
4
5 6 Zones
7
8
9
10
1
2
3
5 6 Zones
4
7
8
9
10
Fig. 9. The spatial density of boulders (all size categories) in the equalarea zones around craters 1 and 4. See the text for discussion.
Fig. 10. The change of the characteristic size of boulders with the distance from craters 1 and 4. See the text for dis cussion.
DISCUSSION
(2) Interpretation of the nature of the units suggests that the ejecta from the crater BoguslawskyD is a more preferable object for investigations. In the ejecta material, one may find and analyze the substance that predates the formation of the largest and oldest impact basin—the South Pole–Aitken basin—and goes back to the most ancient periods of the geological history of the Moon.
Geological study of the structure of the crater Boguslawsky floor selected as a target for the Luna Glob mission allows us to infer the following. (1) The crater’s floor is composed of the material of four complexes: two units of rolling plains (the rpw and rpc units near the crater’s walls and in the central part of the floor, respectively), flat plains (the fp unit), and ejecta from the crater BoguslawskyD (the ejf unit). Within the western landing ellipse (72.9° S, 41.3° E), flat plains dominate, while ejecta from the crater BoguslawskyD dominates in the eastern one (73.9° S, 43.9° E).
(3) The rockiness degree of the surface of ejecta from the crater BoguslawskyD was estimated from the radar data (the circular polarization ratio, RCP) acquired with the MiniRF instrument onboard the LRO spacecraft and from the direct counting of the
Table 3. Spatial density of boulders in different intervals of diameters around craters 1 and 4 Diameter interval
Crater 1
from, m
to, m
Mean diameter, m
1.0 1.4 2.0 2.8 4.0 5.7 8.0 11.3
1.4 2.0 2.8 4.0 5.7 8.0 11.3 16.0
1.2 1.7 2.4 3.4 4.8 6.7 9.5 13.5
Crater 4
density
statistical deviation
density
statistical deviation
Density difference between craters 1 and 4, %*
72.6 58.0 32.2 10.6 2.4 0.5 0.1 0.01
0.8 0.7 0.5 0.3 0.1 0.1 0.03 0.01
53.2 41.1 19.3 5.4 1.0 0.1 0.01 –
0.8 0.7 0.5 0.3 0.1 0.04 0.01 –
–26.8 –29.1 –40.0 –49.2 –56.4 –73.8 –89.2 –
* Negative values mean that the spatial density of boulders near crater 4 is smaller than that near crater 1. SOLAR SYSTEM RESEARCH
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Cumulative spatial density of boulder, 10000 m–1
100
10
Crater 1 (Curve slope: –4.29)
1
0.1
Crater 4 (Curve slope: –5.78)
0.01
0.001 1
10 Boulder diameter, m
100
Fig. 11. The sizefrequency distribution of boulders (totally in all zones) around craters 1 and 4. See the text for discussion.
spatial density of boulders distinguishable in the superresolution images (0.5 m/pixel, the NAC cam era onboard the LRO spacecraft). (4) The images of ultrahigh resolution show that there are virtually no boulders larger than 0.5 m on the surface of ejecta from the crater BoguslawskyD. However, the radar data show numerous clusters of the boulder material within the ejecta. The comparison of the CPR values and the spatial density of boulders demonstrates no correlation between these parame ters. No correlation and a small spatial density of visu ally detected boulders suggest that the rock debris located in the subsurface layer sounded by radar (1– 1.5 m thick) is the main contributor to the CPR values. (5) From the superresolution images, the number and sizes of boulders near the most rocky craters of small sizes (craters 1 and 4) on the floor of the crater Boguslawsky were determined.
(6) The spatial density of boulders near crater 1 (105 boulders per 10000 m2) is approximately 28% higher than that near crater 4 (75 boulders per 10000 m2). Such a difference in the density indicates that crater 4 is approximately 30–50 Myr older than crater 1 (Basilevsky et al., 2013). (7) The spatial density of boulders drops with the distance from the crater in the both cases, 1 and 4. For these craters, the densities decrease in parallel to each other, which suggests that the intensity of destruction of boulders is constant in time. (8) The diameters of rock fragments near crater 4 is in a narrower range (1–8 m) than those for crater 1 (1–13 m), and they are distributed more uniformly in the vicinity of the crater. The size distribution of boul ders with the distance from the rim of crater 4 is approximated with the curve, whose slope is –0.02, while the slope of the approximating curve for the boulders around crater 1 is –0.05. The gentler slope of the curve for the older crater 4 is evidently connected with the smoothing of the rock debris sizes with time. (9) The sizefrequency distribution of all rock frag ments for craters 1 and 4, regardless of the distance from the rim, reveals the prevailing destruction of large boulders as the surface becomes older. The spatial density of boulders in the interval of diameters from 2.8 to 4 m for crater 4 is approximately 50% less than that for crater 1, while the spatial density of boulders in the diameter range from 8 to 11 m around crater 4 is 90% less than that around crater 1. These differences cause the different slopes of the curves approximating the sizefrequency distribution of fragments: it is ⎯4.29 around the younger crater 1, while the older cra ter 4 shows this quantity at –5.78. (10) Some large boulders near crater 1 demonstrate the rolling traces as grooves of 30–50 cm deep. There are no such rolling traces near crater 4, which suggests that the regolith layer with a thickness of first tens of centimeters was reworked by meteoritic bombardment during the time interval between the formations of cra ters 1 and 4, 30–50 Myr. This allows one to estimate the reworking intensity for a thin surface layer as 0.01 m/Myr, which actually coincides with the esti mate of the reworking rate for a substantially thicker layer (first tens of meters) obtained from the results of the study of destruction of small craters on the Moon (Fassett and Thomson, 2014). CONCLUSIONS The paper considered the results of the study of the geological structure of the crater Boguslawsky floor selected as a primary target for the LunaGlob mission. The deplanate floor of the crater is covered by the material ejected from the remote craters and the crater BoguslawskyD located on the eastern inner slope of the crater Boguslawsky. It is highly probable that, in the ejecta material of the crater BoguslawskyD, one may find and analyze the substance that predates the SOLAR SYSTEM RESEARCH
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formation of the largest and oldest currently known impact basin on the Moon—the South Pole–Aitken basin. The rockiness degree of the crater Boguslawsky floor has been estimated from the radar data and the manual boulder counts in the superresolution images (NAC, 0.5 m/pixel). Comparison of the radar data to the results of the photogeological analysis shows that the main contributor to the radar signal is the rock debris located in the subsurface layer sounded by radar (1–1.5 m), while there are practically no boulders on the surface. The two most rocky regions on the crater Boguslawsky floor are associated with the relatively fresh impact craters of 300–400 m diameter. The spa tial density of boulders near the craters suggests that one of them is 30–50 Myr older than the other. For both of these craters, the spatial density of boulders drops with the distance from their rims. The rate of the decrease in the boulder spatial density is the same for both craters, which points to the temporally constant intensity of the fragmentation of boulders. The size distribution of boulders with the distance from a rim of the older crater is approximated by the curve with a slope of –0.02, while the curve slope for the younger crater is –0.05. The gentler curve slope for the older crater is obviously connected with the equalizing of sizes of the rock debris with time. The sizefrequency distribution of all rock fragments for the both craters, regardless of the distance from the rim, shows that mainly large boulders first crumble away as the age of the surface increases. Some large boulders near the young crater demonstrate the traces of rolling, while such traces are absent for the boulders near the older crater. This allows us to estimate the intensity of the reworking of a thin surface layer at 0.01 m/Myr. ACKNOWLEDGMENTS The investigations were performed in GEOKHI RAS with the support of the Space Research Institute of RAS in terms of the geologic mapping and interpre tation of the material units in the crater Boguslawsky floor (contract no. 13 2013 of August 23, 2013; A.M. Abdrakhimov, A.T. Basilevsky, and M.A. Ivanov). The parameters of the spatial and size frequency distribution of boulders were estimated in MIIGAiK with the support of the Russian Scientific Foundation (project no. 142200197; A.T. Basilevsky, M.A. Ivanov, A.A. Kohkanov, and I.P. Karachevtseva). The work of J.W. Head, A.T. Basilevsky (in part), and M.A. Ivanov (in part) is supported by the NASA LRO mission, LOLA experiment team (Grants NNX11AK29G and NNX13AO77G) and NASA Solar System Exploration Research Virtual Institute (SSERVI) Grant for Evolution and Environment of Exploration Destinations under cooperative agree ment number NNA14AB01A at Brown University in respect of providing the data accessibility. SOLAR SYSTEM RESEARCH
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REFERENCES Bazilevskii, A.T., The way to estimate power and degree of lunar regolith processing according to craters’ abun dance, Kosm. Issl., 1974, vol. 12, no. 4, pp. 606–609. Basilevsky, A.T., On the evolution rate of small lunar cra ters, Proc. 7th Lunar and Planetary Sci. Conf., Houston, 1976, pp. 1005–1020. Basilevsky, A.T., Head, J.W., and Hörz, F., Survival times of metersized boulders on the surface of the Moon, Planet. Space Sci., 2013, vol. 89, pp. 18–126. Black, G. and Campbell, D.A., Rhea’s surface: ice proper ties measured by radar, Bull. Am. Astron. Soc., 2004, vol. 36, p. 1123. Boynton, W.V., Droege, G.F., Mitrofanov, I.G., McClana han, T.P., Sanin, A.B., Litvak, M.L., Schaffner, M., Chin, G., Evans, L.G., Garvin, J.B., Harshman, K., Malakhov, A., Milikh, G., Sagdeev, R., and Starr, R., High spatial resolution studies of epithermal neutron emission from the lunar poles: constraints on hydrogen mobility, J. Geophys. Res., 2012, vol. 117, no. 3, p. E00H3. Doi: 10.1029/2011JE003979 Campbell, D.A., Chandler, J.F., Ostro, S.J., Pettengill, G.H., and Shapiro, I.I., Galilean satellites: 1976 radar results, Icarus, 1978, vol. 34, pp. 254–267. Fassett, C.I. and Thomson, B.J., Crater degradation on the lunar maria: topographic diffusion and the rate of ero sion on the Moon, J. Geophys. Res., 2014, vol. 119, pp. 2255–2271. doi:10.1002/2014JE004698 Feldman, W.C., Lawrence, D.J., Elphic, R.C., Barra clough, B.L., Maurice, S., Genetay, I., and Binder, A.B., Polar hydrogen deposits on the Moon, J. Geophys. Res., 2000, vol. 105, pp. 4175–4195. Feldman, W.C., Maurice, S., Lawrence, D.J., Little, R.C., Lawason, S.L., Gasnault, O., Wiens, R.C., Barra clough, B.L., Elphic, R.C., Prettyman, T.H., Stein berg, J.T., and Binder, A.B., Evidence for water ice near the lunar poles, J. Geophys. Res., 2001, vol. 106, pp. 23231–23252. GarrickBethell, I. and Zuber, M.T., Elliptical structure of the lunar South PoleAitken basin, Icarus, 2009, vol. 204, pp. 399–408. Harmon, J.K., Arvidson, R.E., Guinness, E.A., Camp bell, B.A., and Slade, M.A., Mars mapping with delay Doppler radar, J. Geophys. Res., 1999, vol. 104, pp. 14065–14089. Hiesinger, H. and Head, J.W., Lunar South PoleAitken impact basin: topography and mineralogy, Lunar Planet. Sci, 2004, vol. 34, abstr. no. 1164. Hiesinger, H., van der Bogert, C.H., Pasckert, J.H., Schmedemann, N., Robinson, M.S., Jolliff, B., and Petro, N., New crater sizefrequency distribution mea surements of the South PoleAitken basin, Lunar Planet. Sci, 2012, vol. 43, abstr. no. 2863. Hiesinger, H., Ivanov, M., Pasckert, J.H., Bauch, K., and van der Bogert, C.H., Geology of the Lunar Glob land ing sites in Boguslawsky crater, Moon, Lunar Planet. Sci., 2014, vol. 45, abstr. no. 2370. Hörz, F., Cintala, M.J., See, T.H., Cardenas, F., and Thompson, T.D., Collisional fragmentation of grano diorite targets by multiple impact events, Lunar Planet. Sci, 1985, vol. 26, pp. 364–365.
382
IVANOV et al.
Ivanov, M.A., Abdrakhimov, A.M., Basilevsky, A.T., Dixon, J.L., Head, J.W., Chick, L., Vitten, J., Zuber, M.T., Simt, D.E., Mazarico, E., Neish, C.D., and Bassey, D.B.J., Geological context of potential landing site of the LunaGlob mission, Solar Syst. Res., 2014, vol. 48, no. 6, pp. 391–402. Ivanov, M.A., Hiesinger, H., Abdrahimov, A.M., Basi levsky, A.T., Head, J.W., Pasckert, J.H., Bauch, K., van der Bogert, C.H., Gläser, P., and Kohanov, A., Landing site selection for LunaGlob mission in crater Boguslawsky, Planet. Space Sci., 2015 (in press). Kneissl, T., van Gasselt, S., and Neukum, G., Mapprojec tionindependent crater sizefrequency determination in GIS environments – new software tool for ArcGIS, Planet. Space Sci., 2011, vol. 59, pp. 1243–1254. Mitrofanov, I., Litvak, M., Sanin, A., Malakhov, A., Golovin, D., Boynton, W., Droege, G., Chin, G., Evans, L., Harshman, K., Fedosov, F., Garvin, J., Kozyrev, A., McClanahan, T., Milikh, G., Mok rousov, M., Starr, R., Sagdeev, R., Shevchenko, V., Shvetsov, V., Tret’yakov, V., Trombka, J., Varenikov, A., and Vostrukhin, A., Testing polar spots of waterrich permafrost on the Moon: LEND observations onboard LRO, J. Geophys. Res., 2012, vol. 117, no. 27, p. E00H27. Doi: 10.1029/2011JE003956. Neish, C.D., Bussey, D.B.J., Spudis, P., Thomson, B., Patterson, G.W., and Carter, L., MiniRF observations in support of LCROSS, Lunar Planet. Sci, 2010, vol. 41, abstr. no. 2075. Neukum, G., Ivanov, B.A., and Hartmann, W.K., Cratering records in the inner Solar System in relation to the lunar reference system, Space Sci. Rev., 2001, vol. 96, pp. 55–86. Nozette, S., Spudis, P., Bussey, B., Jensen, R., Raney, K., Winters, H., Lichtenberg, C.L., Marinelli, W., Cru san, J., Gates, M., and Robinson, M., The Lunar Reconnaissance Orbiter Miniature Radio Frequency (MiniRF) technology demonstration, Space Sci. Rev., 2010, vol. 150, pp. 285–302. Oberbeck, V.R., The role of ballistic erosion and sedimen tation in lunar stratigraphy, Rev. Geophys. Space Phys., 1975, vol. 13, pp. 337–363. Paige, D.A., Foote, M.C., Greenhagen, B.T., Schofield, J.T., Calcutt, S., Vasavada, A.R., Preston, D.J., Taylor, F.W., Allen, C.C., Snook, K.J., Jakosky, B.M., Murray, B.C.,
Soderblom, L.A., Jau, B., Loring, S., Bulharowski, J., Bowles, N.E., Thomas, I.R., Sullivan, M.T., Avis, C., De Jong, E.M., Hartford, W., and McCleese, D.J., The Lunar Reconnaissance Orbiter Diviner Lunar Radiom eter experiment, Space Sci. Rev., 2010, vol. 150, pp. 125–160. Pike, R., Apparent depth/apparent diameter relation for lunar craters, Proc. 8th Lunar Sci. Conf., 1977, pp. 3427–3436. Shevchenko, V.V., Chikmachev, V.I., and Pugacheva, S.G., Structure of the South PoleAitken lunar basin, Solar Syst. Res., 2007, vol. 41, no. 6, pp. 447–462. Spudis, P.D., Reisse, R.A., and Gillis, J.J., Ancient multir ing basins on the Moon revealed by clementine laser altimetry, Science, 1994, vol. 266, pp. 1848–1851. Spudis, P., Nozette, S., Bussey, B., Raney, K., Winters, H., Lichtenberg, C.L., Marinelli, W., Crusan, J.C., and Gates, M.M., MiniSAR: an imaging radar experiment for the Chandrayaan1 mission to the Moon, Curr. Sci., 2009, vol. 96, pp. 533–539. Spudis, P.D., Bussey, D.B.J., Baloga, S.M., Butler, B.J., Carl, D., Carter, L.M., Chakraborty, M., Elphic, R.C., Gillis, A., Davis, J.J., Goswami, J.N., Heggy, E., Hill yard, M., Jensen, R., Kirk, R.L., Lavallee, D., McKer racher, P., Neish, C.D., Nozette, S., Nylund, S., Palse tia, M., Patterson, W., Robinson, M.S., Raney, R.K., Schulze, R.C., Sequeira, H., Skura, J., Thompson, T.W., Thomson, B.J., Ustinov, E.A., and Winters, H.L., Ini tial results for the north pole of the Moon from Mini SAR Chandrayaan1 mission, Geophys. Rev. Lett., 2010, vol. 37, p. L06204. Doi: 10.1029/2009GL042259 Stöffler, D., Ryder, G., Ivanov, B.A., Artemieva, N.A., Cin tala, M.J., and Grieve, R.A.F., Cratering history and lunar chronology, Rev. Mineral. Geochem., 2006, vol. 60, pp. 519–596. StuartAlexander, D.E., Geological map of the central far side of the Moon, USGS Map. I1047, 1978. Wilhelms, D.E., Howard, K.A., and Wilshire, H.G., Geo logic map of the south side of the moon, USGS Map I 1192, 1979. Wilhelms, D.E., The geologic history of the Moon, USGS Spec. Pap, 1987, no. 1348.
Translated by E. Petrova
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