Most moons are either round and smooth, or lumpy pieces of space rock.
大多数卫星要么是圆形的，要么是光滑的，要么是块状的太空岩石。
Space Rock, Neo-Psychedelia, Alternative.
太空摇滚，新迷幻，另类。
Can you imagine what would happen if Earth collided with a huge space rock?
你能够想像地球如果撞上太空中的一颗巨大石块会怎么样吗？
The proportion of empty space in a rock is known as its porosity.
岩石中空隙的比例被称为孔隙度。
The proportion of empty space in a rock is known as its porosity.
岩石中空隙的比例被称为孔隙度。
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