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Space

A new formula for defining a planet still keeps Pluto out of the club

The official definition of a planet, which famously saw Pluto demoted to dwarf planet status in 2006, doesn't really work for worlds outside of our solar system. Now there is a fix – but Pluto is still left out

By Jonathan O’Callaghan

16 July 2024

Pluto is a dwarf planet

NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

A mathematical formula to determine whether objects in space should be classed as a planet could make it easier to identify objects around other stars – but it is bad news for anyone hoping that Pluto could regain its planethood.

In 2006, the International Astronomical Union (IAU) infamously demoted Pluto from planet to dwarf planet status in a controversial decision that left our solar system with eight planets. The IAU cited the fact that Pluto hadn’t cleared its orbit of other debris as a critical factor in…

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