So Saturn might once have had more-one of which could have had a rocky core surrounded by a shell of water ice.
因此,土星也许曾经拥有多个颗卫星,其中一颗可能是冰层包裹着岩石内核的样子。
2
Europa is covered in a shell of water ice that's thought to hide an ocean of liquid water below. Liquid water is a key ingredient for life as we know it.