Apollo asteroids pose a threat to our planet as they routinely cross Earth's orbit.
阿波罗型小行星因定期地穿越地球轨道而构对地球的威胁。
So, the planet moves on its orbit.
行星在它轨道上运动。
The planet then spiralled out to take up its present orbit.
而这颗行星就以螺旋线的形式游弋到现在所占据的轨道上。
There is, however, a planet known to orbit backwards around its parent star.
然而，还有一颗绕着母星逆行的行星。
Messenger is the first spacecraft to go into orbit around the planet.
信使号探测器是第一进入行星轨道的航天器。
Science magazine reports that the mysterious "Planet X" moves in a distant orbit beyond Neptune.
据《科学》杂志报道，这颗神秘的X行星的运行轨道远在海王星之外。
It is the fourth planet in orbit around the star Felix.
它是围绕恒星费利克斯旋转的第四颗行星。
The planet is probably in orbit around a small star.
这颗行星可能正环绕着一颗小恒星运行。
Accordimg to the definition, a planet must have a clear neighbourhood around its orbit.
根据定义，一颗行星必须能够清除其轨道附近的其它天体。
The orbit of every planet is an ellipse with the Sun at a focus.
第一定律（轨道定律）：所有行星都沿各自的椭圆轨道运动，太阳在该椭圆的一个焦点上。
It won't land on Mars but will orbit and monitor the planet.
萤火一号“将不会登陆火星，而是在其轨道上运行并进行探测。”
A heavenly body kept in orbit around a planet by gravitational force.
一种因引力而沿轨道绕行星旋转的天体。
A heavenly body kept in orbit around a planet by gravitational force.
一种因引力而沿轨道绕行星旋转的天体。
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