noun🔗Share原行星，行星胚胎。 An astronomical object, approximately the size of the Moon, formed from the mutual gravitational attraction of planetesimals; they are thought to collide with each other and slowly form planets"The astronomers believe a protoplanet, about the size of our Moon, collided with another one billions of years ago, eventually forming the planet Earth. "天文学家们认为，大约几十亿年前，一颗**原行星（一种像月亮大小的行星胚胎）**与另一颗发生了碰撞，最终形成了地球。astronomyspacescienceChat with AIVocabulary GamePractice Reading
