Technical Report 月の死の湖と虹の入り江の陥没地形周辺の年代測定
Model age determination of the areas around the Lacus Mortis pit and the Sinus Iridium pit on the Moon

櫛田, 果鈴  ,  齋藤, 優里  ,  春山, 純一  ,  Kushida, Karin  ,  Saito, Yuri  ,  Haruyama, Junichi

JAXA-RM-15-007pp.1 - 18 , 2016-03-08 , 宇宙航空研究開発機構(JAXA) , Japan Aerospace Exploration Agency (JAXA)
本稿では,月の中緯度帯にみつかった2 つの陥没地形(pit)1)死の湖(44.962N, 25.610E) の陥没地形と,2)虹の入り江(45.63N, -28.80E)の陥没地形について,その周辺の溶岩噴出年代決定を行ったことを報告する.こうした陥没地形は,科学的にも興味深く,また, 将来の基地候補である.さらに,中緯度の陥没地形は,低緯度に比べて温度の振幅が小さい点で基地候補としてはより優れていると考えられる.我々は,10 m/画素の解像度を持つSELENE 搭載地形カメラによる画像データを用いて,陥没地形周りのクレータ個数密度分布を測定し,クレータ年代学を適用することで,年代の決定を行った.地質の分類には, 地形カメラデータに加えて,SELENE 搭載マルチバンドイメージャの415, 750, 950 nm バンドのデータを利用した.死の湖の陥没地形の周りは33, 35, 38 億年前の少なくとも3 回,虹の入り江の周りは36 億年前に噴出した溶岩流の存在が示唆された.年代の多様性という点で,死の湖の陥没地形の周辺領域が科学的に興味深い.また,死の湖の陥没地形の周辺領域は,虹の入り江の陥没地形の周辺領域よりも直径100-500 m のクレータの個数密度が低くなっていることから,虹の入り江の陥没地形周辺領域に比べ,着陸や陥没地形への接近において,容易であると考えられる.ただし,この死の湖の陥没地形周辺領域では虹の入り江の陥没地形の周辺領域に比べ,直径500 m 以上のクレータの個数密度が高く,探査においては注意を要する.
We report the results of model age determination for the areas around two pits that were discovered in the middle latitude of the Moon: 1) in the Lacus Mortis (44.962N, 25.610E) and 2) in the Sinus Iridium (45.63N, -28.80E). The pits at middle latitudes are sites favorite for lunar base construction and more advantageous than those at lower latitudes because the temperature oscillation at the middle latitudes is smaller than that at lower latitudes. We determined the model ages of the areas based on the crater chronology, measuring crater size frequency distributions using image data acquired by the SELENE Terrain Camera (TC) of 10 m/pixel resolution. We performed the discrimination of geological units using 415, 750, and 950 nm spectral band image data from the SELENE Multi-band Imager, in addition to the TC image data. We obtained model ages of 3.3, 3.5, and 3.8 billion years ago for the areas around Lacus Mortis pit and 3.6 billion years ago for the area around the Sinus Iridium pit. From the view point of variety of lava eruption dates, the area around the Lacus Mortis pit is more interesting than that around the Sinuous Iridium pit. An area around the Lacus Mortis pit has a lower cumulative crater number density for craters of 100 m to 500 m in diameter than that around the Sinuous Iridium pit, which means the area is easier to land near and approach to the pit from the landing point than that around the Sinuous Iridium pit. However, we note the area has a higher crater number density for craters of greater than 500 m in diameter than that around the Sinuous Iridium pit; such lager craters should be paid attention when the Lacus Mortis pit will be explored.
形態: カラー図版あり
Physical characteristics: Original contains color illustrations

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