P13E-01
The Kaguya (SELENE) Mission and Its Lunar Science
Lunar orbiter Kaguya (SELENE) has been successfully launched from Tanegashima Space Center TNSC on
September 14, 2007. Nominal observation for ten lunar days has already passed and fourteen science
instruments are acquiring new data of global Moon to study lunar science in mineralogy, geology, gravimetry,
topography, and plasma environment. Multi-band imager and Spectral profiler definitely analyze mineralogy
of central peaks of central peaked craters. High resolution images of Terrain Camera show new crater
distribution of cratered terrain of farside, Detailed topography and gravitational distribution in farside and
polar area are observed by laser altimetry and four way Doppler tracking of main orbiter flying in farside.
http://www.kaguya.jaxa.jp
P13E-02
Lunar Far Side Gravity From SELENE Mission And Dichotomy of the Moon
Current lunar gravity field models include large uncertainties on the far side of the Moon. We developed a satellite-to-satellite Doppler tracking sub-system (RSAT) on SELENE (KAGUYA). Main function of RSAT is to relay Doppler tracking signals between the main orbiter (MAIN) over the far side and ground-based antenna. When MAIN is orbiting over the far side of the Moon, tracking signal in S band is relayed by Rstar to MAIN. Then MAIN returns the tracking signal to Rstar to downlink a coherent Doppler signal to the antenna. RSAT realizes the first direct observation of the gravity field over the far side of the moon. The most recent lunar gravity models from SELENE enable global gravity anomaly mapping of the Moon up to degrees as high as 100. Gravity anomaly of our new models on the near side is almost identical with that of Lunar Prospector, however, gravity anomaly map on the far side reveals dramatic improvement. Gravity signatures over far-side basins that used to be recognized as linear features are now identified as circular anomaly. New gravity model reveals a marked difference of gravity signatures between the near side and the far side. It has been well known that near-side gravity anomaly is dominated by mascons, that is, positive gravity anomaly indicating mantle uplift beneath basins. In contrast, far-side gravity field is characterized by rings of negative free-air anomaly over basins and large craters. Bouguer gravity anomaly map shows that such negative anomaly can be mostly attributed to topographic depression of basin, and that contribution of Moho variation is minor. Our new models suggest that elastic thickness of lithosphere was thin on the near side while was thick on the far side, and propose an important constraint on the origin of dichotomy.
P13E-03
Lunar radar sounder observations of subsurface layers under the nearside maria of the Moon
The Lunar Radar Sounder (LRS) on-board the Kaguya (SELENE) spacecraft started the lunar surface and subsurface soundings since November 2007 in order to understand the origin and evolution of the Moon. Kaguya is in circular orbit with an altitude of 100 km and an inclination of 90 degrees. Orbital period is about 2 hours. The LRS system transmits a radar signal modulated from 4 MHz to 6 MHz with a pulse width of 200 microsecond and a peak power of about 800 Watts. The range resolution of LRS is 75 m in free space. The pulse repetition frequency of pulse transmission is 20Hz (Ono and Oya, 2000; Ono et al., 2008). After the operation for 10 month, the radar sounder observation covered almost whole area of the lunar surface. Based on the observations performed by Apollo Lunar Sounder Experiment (ALSE), it was reported that there are two reflectors at depths of ~1km and ~2km, or apparent depths of ~3km and ~6km, in Mare Serenitatis (Peeples et al., 1978). Therefore, we have checked LRS data obtained in Mare Serenitatis. However, we could not find such reflectors in the LRS data. Instead, we have discovered prominent reflectors lying at the apparent depths of a few hundred meters. Because the range resolution of ALSE was ~400 m, or ~1200 m in free space, it could not distinguish shallow reflectors as found by LRS. It should be noted that similar peak structures can be also formed by range sidelobes of surface echoes. However, we can conclude the peaks seen in the LRS data are not by range sidelobes. If they are sidelobes, (i) the power ratio of range sidelobe to mainlobe should be constant and (ii) the frequency offset of range sidelobe from mainlobe should also be constant. Neither of them is true in the LRS data. The comparison of B-scan images along parallel orbits also supports the conclusion. We also found that most of neaside maria have subsurface stratifications at depths of several hundred meters as seen in Mare Selenitatis. It suggests that they are common geologic structures in the lunar maria. Based on the intensity of echoes, we can also discuss the electric permittivity and loss tangent of surface medium.
P13E-04
A New Lunar Topographic Map of the Moon by KAGUYA-LALT: The First Precise Topography of the Polar Regions
The Japanese lunar explorer KAGUYA (SELENE) was launched successfully on September 14th, 2007. A laser altimeter (LALT) is on board the main orbiter of KAGUYA. The objectives of LALT are (1) determination of lunar global figure, (2) studies in internal structure and surface processes, (3) exploration of the lunar pole regions, and (4) reduction of lunar occultation data. LALT transmits laser pulses whose time width is about 20 nano-seconds and pulse interval is 1 second. Range accuracy is up to 5m. The range data are transformed to the topography of the moon with the aid of position and attitude data of the main orbiter. From the end of December 2007, LALT started continuous operation and a global topography map with unprecedented resolution was produced. Lunar mean radius is estimated as 1737.15±0.01 km and the COM-COF offset is 1.94 km based on the spherical harmonic model STM359_grid-02 derived from LALT topography. The amplitude of the power spectrum of STM359_grid-02 is larger than that of the previous model at L>30 degrees, which may reflect the process of basin formation and/or crustal evolution. In the polar regions where previous CLEMENTINE altimeter did not cover, many topographic features that were difficult to see on the imagery from spacecraft or ground based radar are discovered. The sunlit rate in the lunar polar regions is estimated by using the polar topographic map made from LALT topography. We found that i) the highest sunlit rate is 93~96 % in both polar regions and ii) the eternal shadow area is smaller than previous estimations. These results will be of great use for the planning of the lunar polar exploration in near future.