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WHY ISN’T PLUTO A PLANET?

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Pluto was until recently considered one of our primary planets. That all changed, however, following the 2005 discovery of another world in the Kuiper Belt. The outer edges of the Solar System were now shown to host multiple tiny worlds, so should they all be counted as planets? If not, then why was Pluto considered one? The following year, the Internatio­nal Astronomic­al Union asked participan­ts to vote on Resolution 5A: Definition of ‘planet’. It produced the following trio of rules for attaining full planetary status: a planet must be in a stable orbit around its star, have enough mass for its gravity to force it into a spheroidal shape, and have cleared the debris field in its orbit. Pluto only passes the first two tests, so has been redesignat­ed as a dwarf planet.

 ?? ?? Pluto’s surface, enhanced in colour by NASA to highlight its features, shows a diverse and fascinatin­g landscape
Pluto’s surface, enhanced in colour by NASA to highlight its features, shows a diverse and fascinatin­g landscape

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