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Is Pluto a Planet?

April 1, 2015
By Libby Strong, Robert Strong and Richard Pollack - Contributing Writers , OVParent

Do you know what a planet is?

Most of us can tell the difference between a planet and a star or asteroid or comet. Astronomers like to group similar objects into categories. Ask almost any school kid 10 years ago (in 2005) what a planet is and they will give you examples from our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Many people used a memory trick to remember the order of the planets by using the first letters of the planets to match the first letters of the phrase My Very Excellent Mother Just Served Us Nine Pizzas.

In 2015, the phrase has changed to My Very Excellent Mother Just Served Us Nachos. But wait! What happened to the pizza? Were is Pluto?

Article Photos

NASA's New Horizons spacecraft mission to Pluto

The story of Pluto started more than 85 years ago. Pluto was discovered pretty much by accident in 1930 by the young American astronomer Clyde Tombaugh.

When Pluto was first found, it was thought to be a planet bigger and more massive than the Earth. Due to a math error in a time before computers, astronomers started searching for a big object thought to be pulling on the outer planet Neptune.

Over time, the math error was found and better observations revealed that Pluto was much smaller than expected, only two-thirds the size of Earth's Moon.

Some astronomers started to wonder if Pluto should be reclassified as something other than a planet. In 2006, an elite club of professional astronomers voted at a meeting of the International Astronomical Union to demote Pluto from its classification as a planet to a new category of smaller astronomical objects with the name "dwarf planet." Not everyone agreed with the new definition. To this day there is still much debate on what is or is not a planet.

On Jan. 19, 2006 NASA launched the New Horizons spacecraft mission to Pluto to study the unexplored farthest planet, its surface features, five known moons and atmosphere. The New Horizons spacecraft will arrive and fly through the Pluto system this summer on July 14.

Here are five planet-related topics for discussion with your family:

1) What characteristics do you think a body in space needs to be called a planet?

2) Do planets need to orbit the sun?

3) What about the nearly 1,800 planet-sized objects found orbiting other stars? Should these be called planets? Why or why not?

4) If the Earth's moon were orbiting the sun and not the Earth it would most likely be called a planet based on its size. How small can an object be and still be called a planet?

5) What if a planet-sized body - say Neptune - were thrown away from the sun and out of the solar system and floating in the space between the stars. Is it still a planet? Why or why not?

We at the SMART-Center think it was easy to demote Pluto to a dwarf planet when even though the most powerful telescopes Pluto was just a fuzzy smudge and its moons were but tiny blurs. However, when the New Horizons spacecraft makes its flyby of Pluto, and high definition images and data come back, the world's astronomers and citizen scientists will have to reevaluate Pluto's status. We think the images will ignite a new appreciation of Pluto as a unique world and that citizen scientists will support a reinstatement of Pluto as a planet. What do you think?

Libby and Robert Strong and Richard Pollack work with the SMART-Center, a science outreach organization, the headquarters of which is located at the SMART Centre Market, 30 22nd St., Wheeling.



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