已确认出10个彗星群，各群的彗星数目有多有少。有一种看法认为，同群的彗星是由一颗大彗星分裂出来的。
经常有彗星被甩出奥尔特云(在太阳系边缘的彗星群)，并靠近地球到肉眼可以观测的距离。
Every so often a comet gets flung out of the Oort Cloud, a swarm of comets on the fringes of the solar system, and gets close enough to Earth for us to see it.
科学家们已发显着显的迹象表明：太阳有一个小弟弟，它是一颗暗星，其偏爱轨道导致彗星群和流星雨周期性降落地球。
Scientists have found compelling evidence that the Sun has a baby brother, a dark star whose eccentric orbit is responsible for periodically showering the Earth with comets and meteorites.
科学家们已发现明显的迹象表明：太阳有一个小弟弟，它是一颗暗星，其偏心轨道导致彗星群和流星雨周期性降落地球。
Scientists have found compelling evidence that the Sun has a baby brother, a dark star whose eccentric orbit is responsible for periodically showering the Earth with comets and meteorites.
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