冥王星及其卫星
据英国《每日电讯报》报道，一些具有影响力的天文学家认为，冥王星应该恢复行星身份。资深太空科学家，包括来自美国宇航局的专家，将于本周对国际天文联会做出的一项有争议的决定提出反对意见，探讨究竟什么样的星体才算行星。
国际天文学联合会负责天文命名。按该会采取的新定义原则，冥王星的行星身份被剥夺，被归入“冥王体(plutoids)”行列。自从70年前发现这颗星体以来，人们一直将它视为是距离太阳最远的一颗行星，但是由于它的体积较小，而且处在太阳系内比较偏远的位置，有些天文学家认为它不应被归入行星行列。
科学家在马里兰举行的一个有关行星的重要会议上，将提出重新恢复冥王星的第九大行星身份的要求。这项会议将于8月14日举行。他们声称，被修改的定义令人感到难以理解，而且它将意味着最近在位于我们的太阳系以外的其他太阳系发现的行星，不能再用这种方法进行定义。根据最近的分类规则，现在所有体积较小而且与太阳之间的距离比第八颗行星——海王星与太阳之间的距离更远的近似球体的天体，都被归入“冥王体”行列。
加利福尼亚州美国宇航局月球科学研究所主管大卫·莫里森说：“以前任何组织从来都没必要重新定义一个人们日常普遍使用的词，因此我认为在这种情况下改变冥王星的身份也没什么道理。天文学家利用‘巨大’和‘侏儒’等形容词描述行星、横行和星系等不同天体子类别，那么为什么冥王星就不能像巨行星——木星那样，继续保持它的矮行星身份。根据我们现在了解的情况，大约有90%的行星都位于我们的太阳系以外，但是根据国际天文联盟的这个定义，它们都不能被归入行星行列。”
科学家在大行星辩论会(Great Planet Debate)上进行发言时，还将提议利用一种根据形状进行分类的简单办法给行星归类。行星科学研究所的马克·赛克斯将在会议上进行辩论，他认为圆度比应该作为行星分离的唯一标准。他表示，这种方法将让我们的太阳系中的行星数量增加到12颗。国际天文联会中那些因循守旧的人对此感到非常担心，他们害怕随着更多较小的天体被发现，太阳系中的行星数量将增加更多。美国自然历史博物馆的尼尔·德格拉斯·泰森博士将会争辩说，冥王星不应该被看成是一颗行星。
Pluto should get back planet status, say astronomers
Pluto should have its status as a planet reinstated, leading astronomers have said.
Senior space scientists, including experts from Nasa, will this week attack a controversial decision by the International Astronomical Union, the body responsible for astronomy nomenclature, to redefine what constitutes a planet.
The new definition adopted by the Union saw Pluto demoted to a new kind of celestial underclass now known as "plutoids".
It had been been known as the furthest planet from the sun since its discovery around 70 years, but saw its status changed because of its small size and remote position in the solar system.
Scientists speaking at a major conference on planets in the Maryland, which starts on Thursday, will call for the icy globe to be reinstated as the ninth planet.
They claim that the revised definitions are confusing and will mean that newly discovered planets in solar systems outside our own can no longer be described as such.
In the current classification, all small and nearly spherical objects orbiting beyond the eighth planet from the sun, Neptune, are now plutoids.
Dr David Morrison, director of the Nasa Lunar Science Institute in California, said: "It has never before been necessary for any organisation to define a word that has been in common every day use so I see no reason why it was necessary on this occasion.
"Astronomers use adjectives such as giant and dwarf to describe different subclasses of objects like planets, stars and galaxies, so why could Pluto not remain as a dwarf planet just as Jupiter is a giant planet.
"Also, around 90 per cent of the planets we know now are outside our solar system, but under the International Astronomical Union’s definition, they cannot be classed as planets."
Scientists speaking at the Great Planet Debate conference will also propose using a simple shape-based mechanism for categorising planets.
Mark Sykes, from the Planetary Science Institute will argue that roundness should be the only category that is applied.
This, he says, will lead to the number of planets in our own solar system increasing to 12.
This has alarmed traditionalists at the International Astronomical Union who fear there will be an ever increasing number of planets in the solar system as more smaller objects are discovered.
Dr Neil deGrasse Tyson, from the American Museum of Natural History, will argue that Pluto does not deserve to be a planet.
Too small: Pluto's classification was changed to plutoid by the International Astronomical Union
