Astronomers are proposing a new definition of a planet, nearly two decades after a previous such change led to Pluto’s demotion. The new definition would add measurable criteria, including considerations of the planet’s mass — and it would still leave Pluto with its dwarf planet status.
Currently, the International Astronomical Union (IAU) defines a planet as a celestial body with three characteristics: It orbits the sun, it’s big enough for gravity to mold it into a roundish shape, and it has cleared away any smaller objects, other than moons and other satellites, surrounding its orbit.
“The problem in the past was, you had a word ‘planet’ but you didn’t have a quantitative definition of it,” Brett Gladman, an astronomer at the University of British Columbia who, along with colleagues, proposed the new definition, told Live Science. The proposal was outlined in a paper published July 17 in The Planetary Science Journal and is scheduled to be presented at the IAU General Assembly in August.
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