碉堡形坑洞 (Rampart Craters) 是一種相當特殊的撞擊坑；目前只在火星以及少數太陽系的衛星表面被發現。這種撞擊坑主要位於火星北半球的中低緯度地區。這類坑洞有著類似台地的結構環繞在坑洞環邊，形成原因一般認為是因為撞擊後的噴發物中含有大量水分。這些坑洞的分布已經被當成是可能的火星地下水或地下冰層位置。另外，它們的形態可以提供關於火星北半球可能曾經有大量液態水時造成的侵蝕與沉積重要資訊。在這篇論文中我們在火星表面的Chryse Planitia選定88個這類坑洞；並在北緯65~80度的區域中選定54個。使用四個環繞火星探測船的影像資料，這些資料來自以下儀器：HRSC (裝設於Mars Express)、MOC (裝設於Mars Global Surveyor)、THEMIS (裝設於Mars Odyssey)、以及HiRISE (High裝設於Mars Reconnaissance Orbiter)；以及地形測量資料來自MOLA (裝設於Mars Global Surveyor) 和 HRSC/DTM (裝設於Mars Express) 以進行此類坑洞的各項研究。我們發現在坑洞直徑在10公里到20公里的範圍內可以看到各種不同型態的坑洞。在坑洞型態、直徑和深度關係的分析上則顯示了各區域地質的差異性。並以各種坑洞高度剖面的資料了解了各種坑洞在結構上的差異。一些被冰層覆蓋的高緯度坑洞則顯示了含冰層可能存在於該區域下極淺處。 Martian rampart craters are a special type of impact crater, which exist on Mars and some planetary satellites in the Solar System. They are located mostly in the mid- and low-latitude regions of the northern hemisphere of Mars. The formation of the plateau-like crater rims has been suggested to be caused by the mixing of the impact ejecta with water vapor during the impact explosion. Their distribution has therefore been used as indicators of potential sites of underground water or subsurface ice. In addition, their shapes and morphologies can provide important information about the erosion and sedimentary processes that occurred during the time when the northern hemisphere of Mars was probably partly covered by water. In this work, 88 craters in Chryse Planitia and 54 other craters located at latitudes between 65°and 80°N are examined using images obtained by instruments on-board various Mars-orbiting spacecraft including HRSC (Mars Express), MOC (Mars Orbiter Camera), THEMIS (Mars Odyssey) and HiRISE (Mars Reconnaissance Orbiter). Topographical data form MOLA (Mars Global Surveyor) and HRSC DTM measurements are used to characterize the physical properties. Here we discover that craters between 10 and 20 km in diameter have a diverse morphology. The relationship between morphology, diameter, and depth show us differences in the local geology. The different structures of different kinds of ramparts can be seen in cross-section. Some high latitude craters have ice caps inside the cavity, but the depth of the ice-rich layer may be very shallow.
