彗星在圆形轨道上形成，但当它们冒险太接近行星时，就会被引力抛入现在的椭圆轨道。
Comets formed in circular orbits but were gravitationally flung into their present-day elliptical orbits when they ventured too close to planets.
这些冰和小岩石粒的松散集合形成了彗星。
Loose collections of these ices and small rocky particles form into comets.
它们与来自彗星的尘埃颗粒结合在一起，形成了巨大的云团。
They combine with dust particles from the comet to form a huge cloud.
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