Announcing the Top 10 Reasons Pluto Is - or Is Not - a Planet
FOR IMMEDIATE RELEASE
Email: [email protected]
When New Horizons launches for Pluto tomorrow, January 17, 2006, it will begin a long journey to the last unexplored planet of our solar system. Or will it? Some scientists claim that Pluto is a Kuiper belt object, while many others, as well as much of the public, argue that Pluto is and always will be our ninth planet.
To celebrate the New Horizons mission and to draw attention to an interesting scientific debate, The Planetary Society issued a worldwide call for the Top 10 Reasons Pluto is - and is not - a planet.
The results are in!
Pluto is a planet because...[Pluto is] god of the Underworld, not god of the Underachieving World. Earl G, Radford, VA
Pluto is not a planet because...It's time to tighten our Kuiper belt and kick out the stragglers. Alan C, San Antonio, TX
"We narrowed down hundreds of entries from around the world to two lists of ten," said Bruce Betts, The Planetary Society's Director of Projects, "with more weight given to tongue-in-cheek responses than the seriously scientific...although some entrants managed to combine both."
Pluto is not a planet because...It doesn't appear to be so inclined. Lyford R, Ventura, CA
Even The Planetary Society's own Board of Directors is split on the question, with Chairman Neil deGrasse Tyson wanting to demote Pluto from the planetary ranks and other members of the Board staunchly defending Pluto's status. Read more on the Society's website about Pluto's status as a planet in essays by Tyson and the Society's Vice-President Bill Nye. The page also includes the complete lists of Top 10 reasons why Pluto is or is not a planet.
Pluto is a planet because...Look what happened after 40 years of arguing about the name of Planet 7 - we got Uranus. George C, San Antonio, TX
Whether one considers Pluto the last planet, the first Kuiper belt object, or something else entirely, the New Horizons mission will powerfully expand our scientific knowledge and the exploration of our solar system. Extensive mission coverage can be found at the Society's website.
Top Ten Reasons Why Pluto Is a Planet
10. Possession is nine tenths of the law. Don C, Santa Cruz, CA
9. Look what happened after 40 years of arguing about the name of Planet 7 - we got Uranus. George C, San Antonio, TX
8. [Pluto is] god of the Underworld, not god of the Underachieving World. Earl G, Radford, VA
7. The solar system will be too sexual if it is no longer "plutonic." Paul K, Gilroy, CA
6. It would annoy Neil Tyson no end NOT to reclassify Pluto, and that makes for good entertainment for the astronomical community. Lonny B, Parsippany, NJ
5. We'd have to rename Plutonium if it wasn't. Transneptunianium? Yuck. Lyford R, Ventura, CA
4. If Pluto isn't a planet, then My Very Eager Mother Just Sewed Us New...What? New what! Doug E, Leicester, UK
3. It annoys people who like tidy categories. Dennis D, Baton Rouge, LA
2. I'd like a few of the things that I learned in grade school still to be true. David S, Kingwood, TX
1. Eight Is NOT Enough. Jim B, Pasadena, CA
Top Ten Reasons Why Pluto Is Not a Planet
10. If 7-8-9 then only 8 planets remain. Greg M, Costa Mesa, CA
9. Pluto fans didn't raise enough money to bribe the members of the IAU (International Astronomical Union). Torsten Z, Germany
8. When my son asks "Why is Pluto a planet, but Ceres isn't?" I want a better answer than "Old people are afraid of change." Joshua B, Seattle, WA
7. Things are tough all over. It's time to tighten our Kuiper belt and kick out the stragglers. Alan C, San Antonio, TX
6. It would be the first planet to melt into a puddle of water and pebbles if it got too warm. Jane, Silver Springs, MD
5. We could retroactively say that Voyager 2 DID complete the Grand Tour of Outer Planets. Lyford R, Ventura, CA
4. As a small body in the outer solar system, Pluto is lowering the property values of its larger neighbors. Dave O, Fenton, MI
3. Pluto is a Disney character who has been in 48 of his own cartoons, which makes him a star, not a planet. Ryan C, North Adams, MA
2. I would finally be able to listen to Holst's "The Planets" without feeling shortchanged. Lyford R, Ventura, CA
1. It doesn't appear to be so inclined. Lyford R, Ventura, CA
- Orbits the Sun - The object should be orbiting the Sun. It cannot be orbiting another planet, or another object. It can only be a satellite of the Sun.
- Be a sphere - The object's 'self-gravity' should be strong enough that it smooths out any (major) bumps or ridges to become a mostly spherical body.
- Cleared its orbital neighborhood - There should not be any other bodies in the object's orbit. During the object's formation, it should have absorbed and cleaned out any debris in its orbit (with the exception of moons, because moons are gravitationally 'caught').
Pluto is not a planet because it fails to meet the third condition.
- Compared to Pluto, Pluto's moon Charon, is pretty large because it is only about half Pluto's size. Both objects orbit a common center of gravity, but Pluto orbits this center of gravity at a much close distance than Charon, so that's why Charon is considered Pluto's moon.
- For every three times Neptune orbits the Sun, Pluto orbits it only twice. This is called a 3:2 orbital resonance. In addition, there is a whole category of objects that do exactly this; they're called Plutinos. Pluto is also a Trans-Neptunian Object (TNO) and these objects orbit the Sun at a farther distance than Neptune does.
- Pluto is also on the borderline of a region in our Solar System known as the Kuiper Belt where many icy bodies (both big and small) orbit the Sun at a very large distance.
Pluto falls into a whole range of objects that it can be included into. It can be considered a Trans-Neptunian Object, Kuiper Belt Object, and a Plutino. Basically, Pluto has not really cleared its orbit. There are too many objects that are similar to Pluto and are both larger and smaller than it is, that share common characteristics.Therefore, instead of being a planet, Pluto is a dwarf planet. Dwarf planets orbit the Sun, are nearly round, have NOT cleared its orbital neighborhood, and does not orbit any other body (not a satellite).
Image Credits: IAU, The IAU Votes; NASA, Pluto's newly discovered Moons; Wikimedia, the New Solar System.
Additional Resource: AstronomyCast: Pluto's Planetary Identity Crisis (Why Pluto isn't a planet)