Atsushi Yamaji

Publications (7)130.68 Total impact

• Article: The global distribution of pure anorthosite on the Moon.

  Makiko Ohtake, Tsuneo Matsunaga, Junichi Haruyama, Yasuhiro Yokota, Tomokatsu Morota, Chikatoshi Honda, Yoshiko Ogawa, Masaya Torii, Hideaki Miyamoto, Tomoko Arai, [......], Hirohide Demura, Yasushi Yamaguchi, Sho Sasaki, Shinsuke Kodama, Junya Terazono, Motomaro Shirao, Atsushi Yamaji, Shigeyuki Minami, Hiroaki Akiyama, Jean-Luc Josset
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  ABSTRACT: It has been thought that the lunar highland crust was formed by the crystallization and floatation of plagioclase from a global magma ocean, although the actual generation mechanisms are still debated. The composition of the lunar highland crust is therefore important for understanding the formation of such a magma ocean and the subsequent evolution of the Moon. The Multiband Imager on the Selenological and Engineering Explorer (SELENE) has a high spatial resolution of optimized spectral coverage, which should allow a clear view of the composition of the lunar crust. Here we report the global distribution of rocks of high plagioclase abundance (approaching 100 vol.%), using an unambiguous plagioclase absorption band recorded by the SELENE Multiband Imager. If the upper crust indeed consists of nearly 100 vol.% plagioclase, this is significantly higher than previous estimates of 82-92 vol.% (refs 2, 6, 7), providing a valuable constraint on models of lunar magma ocean evolution.
  Nature 09/2009; 461(7261):236-40. · 36.28 Impact Factor
• Article: Lunar radar sounder observations of subsurface layers under the nearside maria of the Moon.

  Takayuki Ono, Atsushi Kumamoto, Hiromu Nakagawa, Yasushi Yamaguchi, Shoko Oshigami, Atsushi Yamaji, Takao Kobayashi, Yoshiya Kasahara, Hiroshi Oya
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  ABSTRACT: Observations of the subsurface geology of the Moon help advance our understanding of lunar origin and evolution. Radar sounding from the Kaguya spacecraft has revealed subsurface layers at an apparent depth of several hundred meters in nearside maria. Comparison with the surface geology in the Serenitatis basin implies that the prominent echoes are probably from buried regolith layers accumulated during the depositional hiatus of mare basalts. The stratification indicates a tectonic quiescence between 3.55 and 2.84 billion years ago; mare ridges were formed subsequently. The basalts that accumulated during this quiet period have a total thickness of only a few hundred meters. These observations suggest that mascon loading did not produce the tectonics in Serenitatis after 3.55 billion years ago. Global cooling probably dominated the tectonics after 2.84 billion years ago.
  Science 03/2009; 323(5916):909-12. · 31.20 Impact Factor
• Article: Long-lived volcanism on the lunar farside revealed by SELENE Terrain Camera.

  Junichi Haruyama, Makiko Ohtake, Tsuneo Matsunaga, Tomokatsu Morota, Chikatoshi Honda, Yasuhiro Yokota, Masanao Abe, Yoshiko Ogawa, Hideaki Miyamoto, Akira Iwasaki, Carle M Pieters, Noriaki Asada, Hirohide Demura, Naru Hirata, Junya Terazono, Sho Sasaki, Kazuto Saiki, Atsushi Yamaji, Masaya Torii, Jean-Luc Josset
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  ABSTRACT: We determined model ages of mare deposits on the farside of the Moon on the basis of the crater frequency distributions in 10-meter-resolution images obtained by the Terrain Camera on SELENE (Selenological and Engineering Explorer) (Kaguya). Most mare volcanism that formed mare deposits on the lunar farside ceased at approximately 3.0 billion years ago, suggesting that mare volcanism on the Moon was markedly reduced globally during this period. However, several mare deposits at various locations on the lunar farside also show a much younger age, clustering at approximately 2.5 billion years ago. These young ages indicate that mare volcanism on the lunar farside lasted longer than was previously considered and may have occurred episodically.
  Science 12/2008; 323(5916):905-8. · 31.20 Impact Factor
• Source

  Available from: Hiroshi Takeda

  Article: Lack of exposed ice inside lunar south pole Shackleton Crater.

  Junichi Haruyama, Makiko Ohtake, Tsuneo Matsunaga, Tomokatsu Morota, Chikatoshi Honda, Yasuhiro Yokota, Carle M Pieters, Seiichi Hara, Kazuyuki Hioki, Kazuto Saiki, Hideaki Miyamoto, Akira Iwasaki, Masanao Abe, Yoshiko Ogawa, Hiroshi Takeda, Motomaro Shirao, Atsushi Yamaji, Jean-Luc Josset
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  ABSTRACT: The inside of Shackleton Crater at the lunar south pole is permanently shadowed; it has been inferred to hold water-ice deposits. The Terrain Camera (TC), a 10-meter-resolution stereo camera onboard the Selenological and Engineering Explorer (SELENE) spacecraft, succeeded in imaging the inside of the crater, which was faintly lit by sunlight scattered from the upper inner wall near the rim. The estimated temperature of the crater floor, based on the crater shape model derived from the TC data, is less than approximately 90 kelvin, cold enough to hold water-ice. However, at the TC's spatial resolution, the derived albedo indicates that exposed relatively pure water-ice deposits are not on the crater floor. Water-ice may be disseminated and mixed with soil over a small percentage of the area or may not exist at all.
  Science 10/2008; 322(5903):938-9. · 31.20 Impact Factor
• Source

  Available from: Hiroshi Oya

  Article: Initial Resuls of Lunar Radar Sounder (LRS) Experiment on Board the Kaguya (SELENE) Spacecraft

  Takayuki Ono, Atsushi Kumamoto, Yasushi Yamaguchi, Atsushi Yamaji, Takao Kobayashi, Yoshiya Kasahara, Hiromu Nakagawa, Shoko Oshigami, Hiroshi Oya
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  ABSTRACT: The Lunar Radar Sounder (LRS) on-board the KAGUYA (Selene) lunar orbiter is currently being equipped to provide the data of subsurface stratification and tectonic features in the shallow part (several km deep) of the lunar crust, by using an FM/CW radar technique in HF (~5MHz) frequency range (Ono and Oya, 2000; Ono et al. 2007). Knowledge of the subsurface structure is crucial to better understanding, not only of the geologic history of the moon, but also of the moon's regional and global thermal history of the moon and of the origin of the Earth-Moon system (Yamaji et al., 1998). In addition to the subsurface radar experiment, LRS will provide the spectrum of plasma waves and solar and planetary radio waves in a wide frequency range from 10 Hz to 30 MHz (Kumamoto et al., 2007; Kasahara et al., 2007). After completing all the pre-flight model integration tests, the KAGUYA (Selene) spacecraft has been launched on September 14, 2007. The technique of the instrumentation of LRS is based on the plasma waves and sounder experiments which have been established through the observations of the earth's magnetosphere, plasmasphere and ionosphere on-board Jikiken, Ohzora and Akebono satellites, and extended to observations of the Martian ionosphere as well as surface land shape on-board the Nozomi spacecraft. To provide necessary efficiency for transmission of high-power (800Watts) pulses and detection of reflected echoes with 5MHz frequency, Bi-Stem antennas with length of 15m are equipped. By using digital signal processing techniques for the RF waveform generation and on-board data analyses, it becomes possible to improve the S/N ratio and resolution, as well as capability of data handling for the subsurface sounding of the Moon (Ono and Oya, 2000; Ono et al. 2007). The instrumental and theoretical studies showed that the observations on-board the SELENE spacecraft will provide detailed information about the subsurface structures within a depth of 5 km from the lunar surface, with a range resolution of less than 75 m for a region with a horizontal scale of several tens of km (Kobayashi et al., 2002, 2006). The present state of the LRS passed the initial test. The LRS experiment is now continuing the standard observation phase of the KAGUYA (Selene) spacecraft. This paper provides initial results from the LRS function test and observation on-board the Kaguya (Selene).. 5. Kobayashi T., T. Ono, Estimation of planetary surface roughness using radio sounder A-scope data, J.
  Earth Planets and Space 01/2007; 59(112). · 0.80 Impact Factor
• Source

  Available from: Hiroshi Oya

  Article: Instrumentation and observation target of the Lunar Radar Sounder (LRS) experiment on-board the SELENE spacecraft

  Takayuki Ono, Atsushi Kumamoto, Yasushi Yamaguchi, Atsushi Yamaji, Takao Kobayashi, Yoshiya Kasahara, Hiroshi Oya
  [show abstract] [hide abstract]
  ABSTRACT: The Lunar Radar Sounder (LRS) on-board the SELENE lunar orbiter is currently being equipped to provide the data of subsurface stratification and tectonic features in the shallow part (several km deep) of the lunar crust, by using an FM/CW radar technique in HF (∼5 MHz) frequency range. Knowledge of the subsurface structure is crucial to better understanding, not only of the geologic history of the Moon, but also of the Moon's regional and global thermal history of the Moon and of the origin of the Earth-Moon system. In addition to the subsurface radar experiment, LRS will provide the spectrum of plasma waves and solar and planetary radio waves in a wide frequency range from 10 Hz to 30 MHz. This paper provides the basic function parameter of the LRS system based on the final function test and proposes observation targets and data analysis that will provide important information leading to a greater understanding of the tectonics and thermal history of the Moon.
• Source

  Available from: Hiroshi Oya

  Article: Initial results from the Lunar Radar Sounder Observation on-board the KAGUYA (Selene) Spacecraft

  Takayuki Ono, Atsushi Kumamoto, Yasushi Yamaguchi, Atsushi Yamaji, Takao Kobayashi, Yoshiya Kasahara, Hiroshi Oya
  [show abstract] [hide abstract]
  ABSTRACT: The Lunar Radar Sounder (LRS) on-board the KAGUYA (Selene) lunar orbiter is currently being equipped to provide the data of subsurface stratification and tectonic features in the shallow part (several km deep) of the lunar crust, by using an FM/CW radar technique in HF (~5MHz) frequency range (Ono and Oya, 2000; Ono et al. 2007). Knowledge of the subsurface structure is crucial to better understanding, not only of the geologic history of the moon, but also of the moon's regional and global thermal history of the moon and of the origin of the Earth-Moon system (Yamaji et al., 1998). In addition to the subsurface radar experiment, LRS will provide the spectrum of plasma waves and solar and planetary radio waves in a wide frequency range from 10 Hz to 30 MHz (Kumamoto et al., 2007; Kasahara et al., 2007). After completing all the pre-flight model integration tests, the KAGUYA (Selene) spacecraft was launched on September 14, 2007. The technique of the instrumentation of the LRS is based on the plasma waves and sounder experiments which have been established through the observations of the earth's magnetosphere, plasmasphere and ionosphere on-board Jikiken, Ohzora and Akebono satellites, and extended to observations of the Martian ionosphere as well as surface land shape on-board the Nozomi spacecraft. To provide necessary efficiency for transmission of high-power (800Watts) pulses and detection of reflected echoes with 5MHz frequency, Bi-Stem antennas with length of 15m are equipped. By using digital signal processing techniques for the RF waveform generation and on-board data analyses, it becomes possible to improve the S/N ratio and resolution, as well as capability of data handling for the subsurface sounding of the Moon. The instrumental and theoretical studies had already shown that the LRS observation on-board the SELENE spacecraft is able to provide detailed information about the subsurface structures within a depth of 5 km from the moon's surface, with a range resolution of less than 75 m for a region with a horizontal scale of several tens of km (Kobayashi et al., 2002, 2006). This paper provides initial results from the LRS function test on-board the spacecraft in the lunar orbit.