I think you’re right in that definitions and language do interplay with culture. How it will play out educationally is also something to consider. I did note your thoughts. Sounds as though reaching out to educators about a changing view of the solar system is something your scientific community needs to do more of (just a thought); this is a great time to take advantage of the interest in space that is higher than it has been for quite some time.

Anyway, this was a very thoughtful and enjoyable post – with great pictures, too.

This was an amazing article read and quite in depth regarding Pluto, its role in the Solar System as well as the factoids and falsities surrounding it. I have shared this article and I hope that some of my peers delve into this and find it just as interesting and impacting.

A pleasure to read!

Michael Frost.

Interestingly, according to the IAU definition, no exoplanet qualifies as a planet because the definition specifically states that a planet must orbit the Sun, not a star. Even if that were changed, it still would not account for rogue planets which float freely in space without orbiting any star.

The IAU definition is bad science because it blurs the distinction between tiny, shapeless asteroids and comets on the one hand and objects in hydrostatic equilibrium on the other. Those who argue that Pluto is fundamentally different from the larger planets ignore the fact that it actually shares many of the same intrinsic properties they do. It has geology and weather and is layered into core, mantle, and crust. In fact, Pluto has more in common with Earth than does Jupiter, yet the IAU puts Earth in the same class as Jupiter and excludes Pluto.

Maybe we need a detailed classification system for planets similar to the Herzsprung-Russell Diagram used for stars. Calling dwarf planets “minor planets” is not a good idea because the term “minor planet” is a synonym for asteroids and comets, which dwarf planets are not. At minimum, we should do away with terms like “major” and “minor” when describing planets and instead use descriptive terms such as terrestrial, gas giant, ice giant, dwarf, etc.

I understand the purpose of the current definitions, but I don’t agree with them, and would be happy to see our solar systems number of planets increase as a consequence of letting Pluto be a planet.

thank you for another very good article and the explanation of why it does not make sense from a scientific perspective to get rid of Pluto as a planet. You should be right with saying that it does not bring any benefit to not count dwarf planets to the club of planets. Why then calling it dwarf planet?

Anyhow, as you stated the list of celestial objects in our Solar System is not carved into stone, as last year and also recently again there have been published reports on two new very large planets X and Y that so far might just have been missed. (http://arstechnica.com/science/2015/01/the-solar-system-may-have-two-undiscovered-planets/)

Science is to keep the mind and discourse open, and whenever there should be new evidence, one must not be too proud to accept it and possibly change a model. But of course the history of science knows a lot of examples how this principle was ignored when one’s theory and thereby name suddenly were endangered to become obsolete in the further debate.

To come to an end I want to share a mnemonic that is known in German and which helps to memorise the (as of today) correct order of the planets:

“Mein Vater erklärt mir jeden Sonntag unsere neun Planeten”, translated roughly as “My father explains to me every Sunday our nine planets” and of course stands for: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto.
Actually it would fit better to chose Saturday instead of Sunday. You said it above that Saturday in fact stands for Saturn.

Without Pluto one could now say “Mein Vater erklärt mir jeden Sonntag unseren Nachthimmel”, “My father explains to me every Sunday our night sky”.
But I like the first one more, as since my childhood I have been used to see Pluto as a planet of its own, even if a very small one.

Best regards,
Nico