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

NASA

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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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