Should Pluto be a Planet?

January 29, 2016
Pluto by New Horizon Spacecraft

Close-Up of Pluto by New Horizon Spacecraft on July 13, 2015


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Should Pluto be a planet? Having now seen some of our first-ever close-up pictures of Pluto, let’s re-visit what to many people is a sore subject.

In 2006, the International Astronomical Union (the world body that names the contents of the universe)  demoted Pluto to a Dwarf Planet because it really does not match the other eight.

  • It’s far smaller, with only 4% the mass of even tiny Mercury.
  • And it has a very unplanetlike orbit from every angle. B
  • ut the clincher was finding more Plutos out there. Eris is bigger than Pluto, while Makemake, Quaoar, Sedna, and a few others are almost as large. If Pluto’s a planet, then those others must be planets, too.

It became clear that there’s a Kuiper Belt out there with thousands of small icy unplanetlike bodies, and Pluto’s one of them.  A whole different ball game from the “original eight” planets. So if you’re one of those who’d like to see Pluto called a major planet again, be aware that you’re opening the door to lots more “major planets” that will be tiny ice-balls with odd names, all of which will be smaller than our moon.

Anyway, what’s in a name? Until about a century ago, rabbits were classified as rodents. Then their order was abruptly changed so that now they’re lagomorphs. That’s mostly because they have four incisor teeth instead of two. But hey, they still hop around. So Pluto is Pluto regardless of which mental box we try to make it fit.

Its widespread appeal is helped by its popular name, though most people don’t know that it was originally suggested by a schoolgirl, or that its first two letters, PL, honor the initials of Percival Lowell, the astronomer who tirelessly hunted for it and at whose observatory it was finally found. As for the cartoon dog, IT was originally named Rover. In 1931, a year after Pluto’s discovery, the Walt Disney folks decided to exploit the newly found world’s publicity, and changed the character’s name to that of the planet.

Pluto’s photo by New Horizons on July 13, 2015—plus, a creative interpretation.

Even if it’s been demoted to a dwarf like so many other Disney characters, Pluto is now a whole new world. Especially this month, which the New Horizons craft will send us all the photos it frantically took as it whizzed past—the first-ever spacecraft to visit that strange tiny world.

Tell us what you think of the “new Pluto”—and whether you’re okay with it being  a “dwarf planet.”

About This Blog

Welcome to “This Week’s Amazing Sky,” the Almanac’s hub for everything stargazing and astronomy. Bob Berman, longtime and famous astronomer for The Old Farmer’s Almanac, will help bring alive the wonders of our universe. From the beautiful stars and planets to magical auroras and eclipses, he covers everything under the Sun (and Moon)! Bob, the world’s mostly widely read astronomer, also has a new weekly podcast, Astounding Universe

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Planet Pluto

Pluto is a planet. Some say it is a "dwarf planet". Are not dwarf people also people? Pluto orbits the sun and is shaped like a planet. Just because its orbit is odd doesn't change the fact that it is a planet. Using the size argument, Earth is not a planet when compared to Jupiter. Pluto is a planet.

Pluto is a planet IMHO.

Pluto is a planet IMHO. Thanks for asking the question. I find it funny that someone has determined Pluto should be called something else. If I rename space, will it make me famous? Let's call it dwarf space because we can see only a small portion of it.Am I famous yet? Drat! ;o)

I agree, Pluto will ALWAYS be

I agree, Pluto will ALWAYS be the ninth planet of our Solar System!

As far as I'm concerned,

As far as I'm concerned, Pluto is, was, and always will be a planet. Size should never be an issue. It is not orbiting a planet, therefore it is not a moon. It is a spherical object, therefore it is not an asteroid. Any questions?

For me Pluto has always been

For me Pluto has always been a planet and always will be, I am looking forward to finding out what the new horizon craft photos was able to photo.

In honor of both Clyde

In honor of both Clyde Tombaugh and Percival Lowell, PLUTO deserves to be OUR out there PLANET regardless of how many icebergs are floating around.

Interesting! I hope that

Interesting! I hope that everyone has a nice weekend.


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