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发表时间:2018-11-08内容来源:VOA英语学习网

Which of these is not a requirement for a celestial body to be considered a planet? Must orbit the sun, must clear its path of orbit, must have a moon or must be round. A planet does not need a moon to meet the International Astronomical Union’s definition of a planet.

But as option B indicated, it does have to clear the neighborhood in its path of orbit. Meaning knock other space rocks out of the way if necessary and that's why the International Astronomical Union announced in 2006 that Pluto was no longer a planet. The Union said it was just too small to clear its path. But that decision caused a lot of controversy and not just among those who were taught there were nine planets in our solar system.

New research published in the scientific journal Icarus argues that Pluto should be reinstated to planetary status. A University of Central Florida scientist says that, nobody actually uses the path clearing requirement in their research.

He says his team looked at two centuries worth of materials and found only one study from the early 1800's that used the path clearing requirement.

He adds that the way a celestial body is formed and whether it's big enough to have a spherical shape are more important factors for its classification. The IAU says it hasn't received any formal requests to reevaluate Pluto but that it's good to debate these topics.

下面哪些不是天体被认定为行星需要具备的条件?必须绕太阳运行,必须清除其轨道路径,必须有卫星或必须是圆形的。依据国际天文学联合会对行星的定义,行星不一定要有卫星。

但是如B选项所示,行星必须能够清除其轨道附近的其它物体。这意味着如有必要,行星要将自已轨道上的太空陨石清除掉,这也是国际天文学联合会(简称IAU)在2006年宣布冥王星不再是行星的原因。该联合会表示,冥王星太小,无法清除其轨道。但是这一决定引发了许多争议,因为人们在学校学习到的知识称太阳系中有九大行星,因此人们对此提出了质疑。

另外,发表在科学期刊《Icarus》上的一篇新研究认为,应该恢复冥王星的行星地位。中佛罗里达大学的一名科学家表示,没有人真正地在研究中应用清除轨道这一要求。

他说,他的团队回顾了200年的文献资料,发现只有19世纪早期的一篇研究应用了清除轨道的要求。

他说,天体形成的方式以及天体是否足够大到成为球形是更重要的分类因素。国际天文学联合会表示,他们没有收到任何要求重新评估冥王星地位的正式申请,不过这些论点值得考虑。

来自:VOA英语网 文章地址: https://www.veryv.net/18/11/cnn20180917_4101612Yhh.html