Astronomy Picture of the Day

Explanation: Ganymede has craters within craters within craters. The old surface of the largest moon in the Solar System shows its age by the large amount of these impact features. The above picture released last week shows two old craters with dark floors located in a relatively bright region known as Memphis Facula, a region itself thought created by an ancient collision. The strange dark floors of these craters were themselves created long ago and now house craters of their own. Crater Chrysor, on the left, spans about 6000 kilometers, about half that of crater Aleyn on the right. The robot spacecraft Galileo took the above photograph during a flyby of this moon of Jupiter in June 1996.

木衛三的撞擊坑疊著撞擊坑。 這顆太陽系最大衛星的古老表面，有大量可佐證其年齡的這種撞擊結構。 上面這幅剛發布的影像，呈現2個具有黝黑坑底的古老撞擊坑；它們皆位於稱為孟菲斯亮斑的相對明亮區域裡，而此區域咸認是另一個古老的撞擊事件的產物。 這二個很久前形成的撞擊坑之奇特黝黑坑底上，如今也疊著較晚近才形成的撞擊坑。 左邊的Chrysor坑，跨幅在6000公尺左右，約為右邊Aleyn坑的寬度之半。 無人太空船伽利略號在1996年6月飛越木星的這顆衛星時，拍下了上面這幅影像