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From Planet to Plutoid

Former planet Pluto gets a new name

By Gail Hennessey | null null , null
This illustration shows Pluto, newly named plutoid, from the surface of one of its moons. Pluto is the large disk at center, right. (Photo: NASA, ESA and G. Bacon (STScI))
This illustration shows Pluto, newly named plutoid, from the surface of one of its moons. Pluto is the large disk at center, right. (Photo: NASA, ESA and G. Bacon (STScI))

Pluto—the heavenly body formerly known as a planet—has been given a new name. Stripped of its planet status two years ago, Pluto will be called a plutoid, astronomers have decided. The classification will apply to other objects that are similar to Pluto too.

Plutoid means "Pluto-like."

The International Astronomical Union (IAU) is responsible for classifying all heavenly bodies. At its recent meeting in Oslo, Norway, the group approved the requirements for an object to be classified a plutoid.

A plutoid is defined as a type of dwarf planet that orbits the sun at a distance greater than Neptune. The object must also have enough mass for its own gravi-tational strength to give it a spherical (ball-like) shape.

In addition to Pluto, the IAU named fellow dwarf planet, Eris, a plutoid. Eris is 27 percent larger than Pluto and lies beyond the eighth planet in our solar system, Neptune.

Astronomers said the new classification was necessary as scientists continue to discover many new objects in outer space.

Astronomer Brian G. Marsden of the IAU spoke to Science News about the new naming method. "We just needed the protocol to name the objects," he said. "But there are more plutoids to find and more known ones to name," Marsden added.

The IAU stripped Pluto of its planet status in 2006. Pluto became a dwarf planet when the committee adopted new guidelines for characterizing objects in outer space.

Artist illustration of plutoid, Eris
Artist illustration of Eris and Dysnomia. Eris is the main object, Dysnomia is the small grey disk just above it. (Photo: NASA)

Many in the scientific community still disagree with Pluto's demotion.

"If I had been at the meeting, I would have argued that Pluto is a planet," planetary scientist Dr. Ralph McNutt told Scholastic News. "I would have also added Eris to the list of planets."

McNutt is currently working on NASA's Messenger mission to Mercury. He weighed in on the importance of the IAU's naming decision. "We tend to hang a lot on names, so some real care needs to be taken in making changes."

So, if you're looking for a new mnemonic (something that helps you remember things, like a verse or formula) to help you recall the "classic planets" of our solar system, try this: My Very Educated Mother Just Served Us Noodles. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. No Pluto, or plutoids, required.


Get more news from outer space in this special report from Scholastic News Online.

About the Author

Gail Hennessey recently retired from teaching 6th grade social studies in Harpursville, New York. For more information and activity ideas, visit her Web site at

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