Pluto Was a Planet

Tuesday, December 08, 2009

Astrophysicist and director of the American Museum of Natural History’s Hayden Planetarium Neil deGrasse Tyson looks at the fate of Pluto, which was long considered the ninth planet in our solar system until it was demoted to a "dwarf planet" in 2006. In The Pluto Files: The Rise and Fall of America’s Favorite Planet, he reconstructs Pluto’s origins, place in pop culture, and why its place in the pantheon of planets was revoked.


Neil DeGrasse Tyson

Comments [21]

Camille Allen from poughkeepsie NY

Dr.Tyson is amazing! im 12 years old and i love him!

Jan. 19 2010 11:26 AM
Mark from Texas

If a *planet* the size and mass of Mercury, which wouldn't "clear its orbit," whatever the hell that's supposed to mean, were ever discovered in the Kuiper Belt, it would be interesting to see how the dynamicists explain how it isn't a planet but Mercury is.

I don't know where Tyson got the ridiculous idea that the position of those of us who recognize that Pluto is a planet has anything to do with cartoon dogs, but if he really believes that, he needs to get out more.

Dec. 14 2009 05:16 PM
Kevin Heider from Sacramento, CA (8 minutes from the Terminator)

That was a good talk Neil. It is reasonable to group Pluto in a class of spherical objects that are more notable than asteroids but are not dominant in their orbit.

The idea behind the IAU definition is to clear the orbit or control the orbit (of similarly sized objects). In this case there are 6 theoretically spherical objects (based on Spitzer diameter estimates) in a 2:3 resonance with Neptune. Objects in the 2:3 resonance are known as Plutinos. These 6 spherical objects in the 2:3 resonance are: Pluto, 90482 Orcus, 28978 Ixion, (84922) 2003 VS2, 38628 Huya, and (208996) 2003 AZ84.

Any definition can be nitpicked. It would also be weird to call Pluto a planet based on geophysical characteristics and then exclude Triton, Titan, Europa, etc.

I still prefer to classify planets as either special (the 8 major dynamical bodies), or as a very inclusive group including spherical secondary planets. In the latter case we would already have about 70+ planets in the Solar System. We would have 8 dominant, ~18 secondaries, and 40-60 likely dwarfs.

-- Kevin Heider

Dec. 10 2009 09:28 PM
Laurel Kornfeld from Highland Park, NJ

Pluto is still a planet, and neither it nor the issue is dead. Only four percent of the IAU voted on the controversial demotion, and most are not planetary scientists. Their decision was immediately opposed in a formal petition by hundreds of professional astronomers led by Dr. Alan Stern, Principal Investigator of NASA’s New Horizons mission to Pluto. One reason the IAU definition makes no sense is it says dwarf planets are not planets at all! That is like saying a grizzly bear is not a bear, and it is inconsistent with the use of the term “dwarf” in astronomy, where dwarf stars are still stars, and dwarf galaxies are still galaxies. Also, the IAU definition classifies objects solely by where they are while ignoring what they are. If Earth were in Pluto’s orbit, according to the IAU definition, it would not be a planet either. A definition that takes the same object and makes it a planet in one location and not a planet in another is essentially useless. Pluto is a planet because it is spherical, meaning it is large enough to be pulled into a round shape by its own gravity--a state known as hydrostatic equilibrium and characteristic of planets, not of shapeless asteroids held together by chemical bonds. These reasons are why many astronomers, lay people, and educators are either ignoring the demotion entirely or working to get it overturned.

Dec. 09 2009 01:35 AM
Amy from Manhattan

Erica [8]--that's what I thought too, but Merriam-Webster's etymology connects it to a Greek root, "plein," that means "flow." How that leads to "rule by the rich" it doesn't explain.

Dec. 08 2009 02:11 PM
Amy from Manhattan

Weren't the estimates off considerably the last time a near-Earth object came close to us, just in the last year or 2?

Dec. 08 2009 01:56 PM

Does he believe that Cosmic Rays are the cause of Global Warming?

Dec. 08 2009 01:54 PM
Michaelanthony Mitchell from New York

I'm not sure about Erica's comment regarding the etymology of "plutocracy," but a look in the dictionary shows that "ploutos" is a Greek word for "wealth." That may indeed be connected to the chthonic god Pluto, but the Greek word "ploutokratia" is our word's closest relative.

Dec. 08 2009 01:48 PM
Ashton from Chelsea, Manhattan

It's segments like this and the earlier one about wheat that make me feel that I have learned more during my seven years of retirement listening to WNYC than I ever did during all of my classroom studying up to and including my undergraduate degree.

Dec. 08 2009 01:46 PM

What do we know about planets in other solar systems?

Dec. 08 2009 01:46 PM
Martin from Manhattan

Pluto, as god of the Underworld presided over the wealth of gems and metals, hence- Plutocracy- rule by the wealthy

Dec. 08 2009 01:43 PM
Max from Brooklyn

All I'm saying is, now how will that phrase used to memorize the planets in order read: My Mother Just Served Us Nine _______. Totally ruined. Existentially left hanging.

Dec. 08 2009 01:43 PM
Laurie Spiegel from Tribeca

Maybe Disney's Pluto for some, but when I was a small child and read about Pluto for the first time in our family's World Book Encyclopedia, I was drawn to it because it was the littlest planet, like me as a child, the furthest away, all the way out there in the cold, and the youngest one in terms of our awareness (the last planet added to the list). It was not a Disney dog but a child's identification with the Underdog of the Planets.

So of course there was internal reaction when it got bumped from the family of planets.

Dec. 08 2009 01:41 PM
Erica P. from NJ

re: plutocracy. Pluto/Hades, being the god of the underworld, was also god of the earth's riches (gems, precious metals, etc.) Most of the major Greek and Roman deities wore many hats.

Dec. 08 2009 01:41 PM

Don't forget that Disney recruited all these German scientists post WWII with dubious records..

Dec. 08 2009 01:37 PM
hjs from 11211

5 bob
agreed!! nothing new in 3 years????

Dec. 08 2009 01:34 PM
bob from NYC

why this topic is still so important? enough already. done. pluto planet. gone. dead. just a huge rock.
i believe mr. tyson has many other interesting stories to tell. r

Dec. 08 2009 01:33 PM

I read the book "Death by Black Hole" I found it to be useful for a neophyte like me. My only suggestion is that I wish you had included some diagrams or pictures to make it easier for me to understand some of the topics you wrote about.

I wound up having to reference the internet/wikipedia to make things clearer for me.

Dec. 08 2009 12:55 PM
Jonathan from Brooklyn

Dr. Tyson- Is it true that Mercury used to be a larger planet, but, because of its proximity to the Sun, most of it has burned away?

Dec. 08 2009 10:54 AM
Jonathan Montero from Buffalo

I agree with George. I've been noticing people listening to Michio Kaku's lectures on 3 Civilizations as well. DR. TYSON WE NEED YOU NOW!

Dec. 08 2009 07:46 AM
George from Bay Ridge

Please debunk the Nibiru 2012 nonsense.

Dec. 08 2009 04:36 AM

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