What is a Planet?

By Matthew Williams January 30, 2017
What is a Planet?

History of the Term:

Working Group on Extrasolar Planets:

2006 IAU Resolution:

  • A planet is any object in orbit around the Sun with a diameter greater than 2000 km. (eleven votes in favour)

  • A planet is any object in orbit around the Sun whose shape is stable due to its own gravity. (eight votes in favour)

  • A planet is any object in orbit around the Sun that is dominant in its immediate neighbourhood. (six votes in favour)

  • NASA: Solar System Exploration - Planets

  • Wikipedia - Definition of Planet

  • IAU - 2006 General Assembly

    • Matthew Williams

    Matthew Williams

    Matt Williams is a space journalist, science communicator, and author with several published titles and studies. His work is featured in The Ross 248 Project and Interstellar Travel edited by NASA alumni Les Johnson and Ken Roy. He also hosts the podcast series Stories from Space at ITSP Magazine. He lives in beautiful British Columbia with his wife and family. For more information, check out his website.