Pluto to Regain Planet Status? (November 23, 2010)

Posted: November 23, 2010 by Mike Hubbartt in Academia, Space Exploration
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By Mike Hubbartt, © Copyright 2010, All Rights Reserved.

I’ve been an amateur astronomer many years, and my schools taught that our solar system has 9 planets. Back in 2005, CalTech Professor Mike Brown discovered Eris, a Pluto-sized planet 9 billion miles from the sun (twice as far away as Pluto) and about the same size as Pluto. This discovery raised the issue of the definition to accurately describe planets. The International Astronomical Union (IAU) met in 2006 and decided the criteria that determines if a body is a planet (original text available from the IAU website) is:

A celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

In the words of the IAU, Pluto and Eris fail to qualify as planets and so they are now classified as dwarf planets. I went to the Wolfram Alpha website and did a search on dwarf planets and received a list of 5 that includes Pluto:

There is a lot more information about the dwarf planets than is shown in this screen capture. Stop by the Wolfram site and check it out here. You might also notice that 1 Ceres, formerly viewed an asteroid in the asteroid belt, is now listed as a dwarf planet. I can handle promotions better than demotions.

Why rehash old news? Because there was a new article by Mike Wall that was published yesterday at Yahoo News (see it here) that asks if the decision to classify Pluto as a dwarf planet is correct based on information we have today. A nice piece (also by Mike Wall) provides new information on Eris’s size and it is available at’s website.

Personally, I think we should reclassify Eris and Pluto as planets. Maybe there are more Pluto-sized bodies further out in the Kuiper Belt. So what? If we can reclassify an asteroid in the asteroid belt, why can’t we add more planets when they are discovered?

What do you think? Should Pluto be returned to the list of planets in our solar system? Chime in if you have an opinion.

Here is a picture of Pluto as it would appear if you were on Charon, a nearby moon:

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