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

By Maitreyi Mantha on March 31, 2017

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,,,

Listen to the Article: Play Audio

Create MLA, Chicago, or APA Website Citation

Create a website citation for this article. We support MLA8, MLA7, APA, and Chicago citation formats.

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.
  • 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
      • 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
            • ribbitfrog
              ribbitfrogFriday, May 19, 2017 at 7:20 am
              I LOVE SCIENCE!!!!!!!
              • batmanFriday, May 12, 2017 at 8:28 am
                hi love it
                • GO news Tuesday, May 9, 2017 at 4:29 pm
                  I can use this for anything! grade year person
                  • dabWednesday, May 3, 2017 at 7:38 pm
                    • dabMonday, May 1, 2017 at 8:02 am

                      Recent Comments

                      Brandon wrote:

                      Minecraft is hard
                      Minecraft As A Mandatory Subject...

                      Brandon wrote:

                      Minecraft is awsome😁💩💩💩💩💩😺
                      Minecraft As A Mandatory Subject...

                      Cat wrote:

                      It isn't cool it is bad
                      Alaska Fishermen Grapple With Ki...

                      JmPlanteras wrote:

                      im not poor im just in wrong pla...
                      Does It Really Rain Diamonds On ...

                      Our Apps and Plugins