g Text Version
Beauty & Self
Books & Music
Food & Wine
Health & Fitness
Hobbies & Crafts
Home & Garden
News & Politics
Religion & Spirituality
Travel & Culture
TV & Movies

Bored? Games!
Take a Quiz
Rate My Photo

Women's Fashion
Small Office/Home Office

All times in EST

Low Carb: 8:00 PM

Full Schedule
g Astronomy Site

BellaOnline's Astronomy Editor


Pluto Is a Dwarf Planet

Clyde Tombaugh discovered Pluto at the Lowell Observatory, Arizona in 1930.

In 2006 the International Astronomical Union (IAU) announced a new classification system in which Pluto became a dwarf planet. The generations of schoolchildren who knew its name as both the ninth planet and the Disney dog were dismayed.

Yet instead of asking why Pluto isn't a planet anymore, a more interesting question is: Why was Pluto ever thought to be a planet?

The story began with the planet Uranus. William Herschel discovered it in 1781, but by 1845 it was puzzling astronomers by not moving as expected.

French mathematician Urbain Le Verrier thought that the discrepancy was due to the gravitational pull of an undiscovered planet. His calculation of this planet's position allowed Johann Galle at the Berlin Observatory to locate Neptune in 1846.

Then half a century later it seemed that another large planet was disturbing the orbits of Neptune and Uranus. The hunt was on for a ninth planet. Perceval Lowell had made predictions about this Planet X, and after his death Lowell Observatory hired Tombaugh to look for it. The object he discovered on February 18, 1930 was assumed to be the missing planet.

However it was soon evident that Pluto was small. Over the years each measurement of Pluto came up with a smaller size. It was far too small to have any gravitational influence on Neptune.

Finally, in the 1990s a highly accurate space probe measurement of Neptune's mass was used to recalculate the orbits of the outer planets. It turned out that there was no anomaly, the orbits were as they should be if undisturbed by a Planet X. Finding Pluto was a lucky accident, though it's a tribute to Tombaugh's thoroughness that he spotted the tiny distant object.

Pluto is not only smaller than several solar system moons, but is also an icy body in an orbit very different to those of the eight planets. Pluto seemed unique until the 1992 discoveries of the first Kuiper Belt objects. The Kuiper Belt contains hundreds of thousands of such icy bodies orbiting at a distance of between 30 and 50 times the distance from the earth to the sun.

The bodies orbiting beyond Neptune are commonly called trans-Neptunian objects. In 2005 the discovery of one that appeared to be larger than Pluto was a further stimulus to a formal definition of a planet. Considering the ensuing controversy, Eris (goddess of strife and discord) was an appropriate name for the new discovery.

We should realize that reclassifying planets is not new. Eighteenth century German astronomer Johann Bode had suggested that there should be a planet between Mars and Jupiter. The discovery of Ceres in 1801 seemed to be confirmation. Unfortunately, half a century later, there were fifteen "planets" in this orbit and astronomers decided they were a new class of objects, and they called them asteroids.

Interestingly, Ceres too has now been classified as a dwarf planet, along with Pluto and Eris and two other trans-Neptunian objects, Makemake and Haumea. Even some who are unconvinced that Pluto is a planet are puzzled by the dwarf planet class, especially since Ceres is quite different to the other four - they have been designated both as dwarf planets and plutoids.

However even if Pluto is not our ninth planet, it has still turned out to be the largest known member of an intriguing new class of solar system object.

There are images related to this article on my Pinterest board "Outer Solar System".

Follow Me on Pinterest
Add Pluto+Is+a+Dwarf+Planet to Twitter Add Pluto+Is+a+Dwarf+Planet to Facebook Add Pluto+Is+a+Dwarf+Planet to MySpace Add Pluto+Is+a+Dwarf+Planet to Del.icio.us Digg Pluto+Is+a+Dwarf+Planet Add Pluto+Is+a+Dwarf+Planet to Yahoo My Web Add Pluto+Is+a+Dwarf+Planet to Google Bookmarks Add Pluto+Is+a+Dwarf+Planet to Stumbleupon Add Pluto+Is+a+Dwarf+Planet to Reddit

Bode and Bode's Law
Uranus and Neptune - Twin Planets
Kuiper Belt
Related Articles
Editor's Picks Articles
Top Ten Articles
Previous Features
Site Map

For FREE email updates, subscribe to the Astronomy Newsletter

Past Issues

Printer Friendly
tell friend
Tell a Friend
Email Editor

Content copyright © 2015 by Mona Evans. All rights reserved.
This content was written by Mona Evans. If you wish to use this content in any manner, you need written permission. Contact Mona Evans for details.


g features
Volans Flies the Southern Skies

Five Astronomical Non-events 2016

Top Ten Astronomy Stories 2016

Archives | Site Map


Past Issues

Less than Monthly

BellaOnline on Facebook

| About BellaOnline | Privacy Policy | Advertising | Become an Editor |
Website copyright © 2016 Minerva WebWorks LLC. All rights reserved.

BellaOnline Editor