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.
