Questions and bridges

Why Is Pluto No Longer a Planet?

In 2006 the International Astronomical Union (IAU) adopted a definition of a planet that Pluto does not fully meet: it has not cleared its orbital neighbourhood of other bodies. So Pluto is a dwarf planet, which describes its category, not its worth.

The short answer

Pluto was not demoted for being small. In 2006 the International Astronomical Union (IAU, the body that sets official names and categories in astronomy) agreed that a planet must:

1. orbit the Sun;
2. have enough mass to be roughly round;
3. have cleared the neighbourhood around its orbit.

Pluto meets the first two but not the third, so it is classed as a dwarf planet.

A little context

Pluto was discovered in 1930 and long counted as the ninth planet. Later, astronomers found many icy bodies beyond Neptune, in the Kuiper Belt. Pluto turned out to be one member of a large family rather than a lone world. Finds such as Eris made a clear definition necessary.

Pluto remains a fascinating place: in 2015 NASA’s New Horizons spacecraft flew past it and revealed mountains, glaciers and a thin atmosphere. More in Pluto.

And astrology?

In the astrological tradition Pluto is associated with deep transformation, treated as a symbol rather than a cause of events. A change in astronomical classification does not erase that cultural meaning. See Pluto in astrology and astronomy vs astrology.

Positions in Astronativa are astronomically exact. The interpretation is for inspiration. · Glossary · Terms · Privacy