46th Lunar and Planetary Science Conference (2015) 1976.pdf

Cold Behavior of the Moon Surface Revealed by CELMS Data from Chang’E-2 Lunar Orbiter. Z. G. Meng1, 2, J. S. Ping2, L. Xiao3, Z. C. Cai4, S. B. Chen1, 1College of Geoexploration Science and Technology, Jilin University, Changchun, 130026, China ([email protected]). 2Key Laboratory of Lunar and Planetary Exploration, National Astronomical Observatories, CAS, Beijing, 100012, China ([email protected]). 3Planetary Science Institute, China University of Geosciences, Wuhan, 430074, China. 4Space Exploration Laboratory, Macau University of Science and Technology, Macau.

Introduction: Knowledge of the thermal interia mal state and other parameters. To eliminate the lati- will provide essential information to understand the tude effect of the CELMS data, the standard TB of basaltic volcanism of the Moon [1, 2]. One of the sci- every latitude is proposed according to the following entific objectives of Chinese Chang’E mission is to criterions: (1) FTA <5%; (2) surface slope <2°; (3) evaluate the thermal emission features of the Moon surface roughness <0.5. FTA is generated with the surface with the microwave radiometer (CELMS) data. method provided by Lucey et al. [9] and the As a key element, cold behavior is essential to charac- Clementine five-band UV/VIS data produced by U. S. terize the thermal behaviors of the Moon surface [2, 3]. Geological Survey (USGS) (http://webgis.wr.usgs. The cold behavior, “Cold Spot”, is first fully studied gov/pigwad/down /moon_dl.htm).The surface rough- by Bandfield et al. using the Diviner data from Lunar ness and slope are estimated with the LOLA data Reconnaissance Orbiter (LRO) [2]. However, due download from http://pds-geosciences.wustl.edu mainly to the shallow penetration depth, the observa- /missions/lro/lola.htm and the method by Smith et al. tions at infrared band are strongly influenced by the [10] and Rosenburg et al.[11]. surface parameters of the Moon [4]. Once the standard TB is identified, it can be em- The penetration depth of the CELMS data can be ployed to generate the normalized TB (nTB) by divid- up to about 10 m in 3 GHz [5], and the CELMS data ing the observed TB by the standard TB at the same are sensitive to the substrate temperature, which pro- latitude, which is expected to eliminate to the varia- vide a potential chance to study the cold behavior of tion of the observed TB with the latitude (Fig.1). Con- the Moon surface. “Cold Spots” had been found at the sidering the extreme lighting conditions due to the brightness map generated with microwave sounder lunar topography, it is difficult to properly calibrate (CELMS) data from Chang’E-1 satellite [3]. The data the Clementine UV/VIS data and CELMS data at the processing method is excellent and is also introduced high latitude regions. Therefore, only nTB within 60° and improved in this paper. from the north hemisphere to the south is presented. Methodology: In this paper, the total 2394 tracks of swath data by microwave sounder onboard 60 1.05 Chang’E-2 satellite from October of 2010 to May of 2011 are collected. The CELMS data are heavily af- 30 fected by the observation time and surface geolocation [2, 6]. The brightness temperature in different obser- 0 1

vation time will weaken the difference resulted from Latitude(°) the lunar regolith layer thickness, components, and -30 surface properties, which will be disadvantageous for 0.95 -60 the application of CELMS data [6, 7]. To eliminate -180 -120 -60 0 60 120 180 the influence from the observation time, the hour an- Longitude (°) gle correction is introduced to generate the brightness Figure 1 Distribution of nTB (3 GHz) at midnight temperature map at 3.0 GHz, 7.8 GHz, 19.35 GHz and 37 GHz at midnight. The spatial resolution is 1°×1°. Results and conclusions: Fig.1 clearly present TB is sensitive to the substrate temperature and TB at that there exists more than twenty apparent cold re- midnight denotes the microwave thermal features of gions at midnight, such as Tycho Crater (43.31°S the lunar regolith, which is selected in our research /11.36°W), Jackson Crater, et al. Even at Copernicus [8]. Crater, Kepler Crater and Aristarchus Crater express- However, the variation of TB with latitude from ing the high nTB, the center of these craters still indi- Equator to the polar regions is up to 200 K at 3 GHz. cates low nTB. On the surface, the cold spot is always This TB variation is much larger than that resulted related to the large craters. But there is no clear rela- from (FeO + TiO2) abundance (FTA), internal ther- tionship between the large craters and the low nTB, 46th Lunar and Planetary Science Conference (2015) 1976.pdf

even if the craters fairly near the aforementioned cra- nTB abnormalities occur surrounding the center of ters don’t yet present low nTB’s. Mare Orientale, which is much different from the sur- Bandfield et al [2] pointed out that all such regions roundings of Mare Humboldtitanum. Combined with with “Cold Spots” occur with high rock abundance the ages of the the maria, the nTB maps of the three and they concluded that it is likely the rock abundance maria may hint the different evolution phases of the resulting in the “Cold Spot” at midnight. However, Moon, which gives rise to a new perspective for the the regions with high rock abundance is widely spread lunar mare evolution. on Moon [2], whereas “Cold Spots” are not always Acknowledges: We would like to thank the Sci- correspondent to the regions with high rock abun- ence and Application Center for Moon and Deepspace dance. This may expresses that rock abundance Exploration for their data support. Thanks also to Dr. doesn’t play an important role on “Cold Spots”. Zheng Yongchun at CAS for pre-processing the Whereas, it is interesting that several craters of this CELMS data. This work was supported by National kind, e.g. Tycho crater, Jackson crater, Copernicus Natural Science Foundation of China (No. 41371332) crater, Kepler crater and Aristarchus crater, are all and the Science and Technology Development Fund of formed at the last 100 M years [12], which indicates, Macau (No. 084/2012/A3). to some extent, that the formation mechanism of these References: [1] Neal, C. R. (2009) Chem Erde, craters and their influence on the structure of the up- 69, 3–43. [2] Bandfield, J. L., et al. (2014), Icarus, per Moon crust may play a dominant role on the “Cold 231, 221-231. [3] Chan, K. L., et al. (2010), Earth & Spot”. Planet. Sci. Lett., 295, 287-291. [4] Fang, T., et al. Moreover, another interesting phenomenon occurs (2014), Icarus, 232, 34-53. [5] Jin, Y. Q., et al. (2003), at the far side of the Moon. Here, Tsiolkovskiy Crater Chin. J. Radio Sci., 18(5), 477-486. [6] Zheng, Y. C., (21.2°S/128.9°E), King Crater (5°N/120.5°E) and et al. (2012), Icarus, 219, 194–210. [7] Meng Z. G., et Fabry Crater (42.9°N/100.7°E) are all showing low al. (2014), Planet Space Sci., 101, 1-11. [8] Jiang, J. nTB abnormality. Meanwhile, the three craters are S., et al. (2011), Science Press, Beijing. [9] Lucey, P. connected by a belt with low nTB, which forms a hid- G. et al. (2000) JGR, 105, E8. [10] Smith, D. E. et al. den linear structure with about 2,000 km long. There (2010) GRL, 37, L18204. [11] Rosenburg, M. A. et al. is not any topography features responsible for this (2011) JGR, 116, E02001. [12] Xiao, Z., et al. (2013), structure. The scale shows that it is likely to be a Earth Planet. Sci. Lett., 376, 1–11. global hidden structure. The hidden linear structure also exists at the east side of South-Pole-Aitken (SPA) basin, and the southeast side of Mare Imbrium along Montes Apenninus. Also, the region near Tycho Cra- ter presents a short but wide hidden structure in north- east direction comprising at least 22 craters with low nTB abnormality. Until now, the hidden structures are fully studied with the topography data [2, 12]. But no materials can interpret the aforementioned hidden structures. Their formation mechanism and their in- fluence on the Moon topography evolution deserve to be further studied. Furthermore, Fig.1 shows that there also exists several hidden circular structures. The most apparent circular structure occurs surround Mare Humbold- tianum. The distribution of nTB indicates that there are two concentric circular hidden structures indicated by a series of “Cold Spots”. Compton crater (55.3°N / 103.8°E) and the north side of Schrodinger basin also present as the circular structure. Whereas, a circular indicated by several low nTB abnormality and the re- gions with low nTB centered at (170°E/53°N) doesn’t have any surface topographic features, which implies that it is a hidden circular structure. Meanwhile, Mare Orientale and Mare Humboldtianum both show multi- ple rings in the topography map. But only four low