planetary space flight

例句：

1. 1. The planetary nebula is a fascinating object in the night sky.
   行星状星云是夜空中一个迷人的物体。
2. 2. The discovery of dinosaurs was made by scientists studying the planetary nebula.
   恐龙的发现是由研究行星状星云的科学家做出的。
3. 3. The planetary nebula is a star that has not yet exploded.
   行星状星云是一个尚未爆炸的恒星。