Scientists Propose Redefining Planets To Include Pluto And Over 100 Celestial Bodies

By on

CCSS NAS-4 Word Search
Solar System with eight planets and one dwarf planet (Photo Credit:

In 2006, the International Astronomical Union (IAU), which promotes and safeguards the science of astronomy, passed a resolution that classified all bodies (except satellites) in our solar system into three distinct categories – planets, dwarf planets, and Small Solar System Bodies. To qualify as a planet, the body had to orbit around the sun, have sufficient mass for its self-gravity to pull it into a round shape, and have cleared the neighborhood around its orbit. Since Pluto did not meet the third criterion, it was downgraded to a dwarf planet.

Now, a group of NASA scientists not only want to restore Pluto’s original status but also reclassify over 100 celestial bodies, including our moon, as planets. The team, led by John Hopkins researcher Kirby Runyon, believes that a planet should be defined by the intrinsic qualities of the celestial body itself, not the external surroundings like its orbit or other objects. They argue that any object in our solar system that hasn’t undergone nuclear fusion and has enough gravitational pull to maintain a round shape, should be called a planet. Under this new definition everything, except for stars, black holes, asteroids, and meteorites, would be considered a planet. This means the number of planets in our solar system would expand from the current eight to almost 110! Among them would be Pluto, our moon, and all newly discovered worlds that are currently dubbed exoplanets.

Pluto (lower right) and, its moon, Charon (upper left) may soon be planets

Though that may sound a lot, especially for students who have to memorize their names, Runyon believes calling them planets will elevate the prestige of the celestial bodies and stimulate the public’s interest. This curiosity will lead to more exploration of our solar system. Additionally, given that most planetary scientists are closely affiliated with geology and other geosciences, the new definition is more relevant than the IAU’s astronomical definition.

While the idea seems valid, the researchers, who presented their arguments at the 48th Lunar and Planetary Science Conference held in Texas from March 20 to 24, still have to obtain approval from the IAU when it meets in Vienna in 2018. Until then, you will have to be satisfied with just eight planets!

Resources: Science Daily,,,

Generate citations in MLA, APA & Chicago formats for this article.

VocabularyPlay Game

affiliatedapprovalastronomicalcriteriondistinctexoplanetsgeologygravitationalintrinsicmassmemorizemeteoritesnuclear fusionorbitprestigerelevantresolutionrestorestimulatevalid

Reading Comprehension (8 questions)

  1. What resolution did the IAU pass in 2006?
  2. What three conditions did a celestial body have to meet to be considered a planet?

Critical Thinking Challenge

Is Runyon’s belief that having more planets will increase public...


Vocabulary in Context

“The team, led by John Hopkins researcher Kirby Runyon, believes that a planet should be defined by the intrinsic qualities of the celestial body itself, not the external...

to use your custom avatar.
  • STuesday, August 15, 2017 at 3:15 pm
    Well they do need to be treated equally so only dwarfs should be planets too many asteroids in one place and a planet does not orbit another planet so asteroids, comets, and moons should not be a planet besides that dwarf planets should be a planet.
    • STuesday, August 15, 2017 at 3:12 pm
      There would be way too many planets
      • OmalThursday, August 10, 2017 at 7:28 am
        I really love science
        • OmalThursday, August 10, 2017 at 7:26 am
          I have to say that is cool
          • OmalThursday, August 10, 2017 at 7:23 am
            Very nice
            • turtlesturtles
              turtlesturtlesTuesday, June 13, 2017 at 6:27 am
              Pluto? Yes, I think should be a planet because it was once actually a planet. Our moon? No, who ever heard of a planet orbiting another planet? Our moon was never a planet, unlike Pluto, so in my opinion I think Pluto should, yes, be a planet as it once was, but as for the moon, no, it should stay a moon
              • CatbugMonday, June 5, 2017 at 8:59 am
                EVERYTHINGS OK!
                • peteral
                  peteralFriday, June 2, 2017 at 2:58 pm
                  Pluto deserves to be a planet. Even though it is not huge, it is big enough to have hydro-static equilibrium.
                  • thWednesday, May 31, 2017 at 9:17 pm
                    Wow I did saw a heart on pluto
                    • LarryWednesday, May 24, 2017 at 10:03 am
                      I still don't agree - moons are not planets - they orbit a planet - you may call them SUB-Planets or planetisimals - but based on mass they are not fully developed planets - IMHO

                      Recent Comments

                      space_fox_x wrote:

                      they desurve a cookie
                      Video Of The Week — 76,017 Domin...

                      Nice wrote:

                      Cool I like spiders
                      Sea Spiders Use Their Guts, Not ...

                      SMARTY_LIVE_ONE wrote:

                      Hey hey I hope they fix it :(
                      Australian Scientists Hope The G...

                      Le magnific wrote:

                      This is so me I love Lego so my ...
                      LEGO's Massive "Home Of The Bric...

                      Our Apps and Plugins