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NASA proposes redefining the word 'planet'


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Havent read the proposal, so if our moon is a planet what is the new definition for a moon.

A moon should be defined as a natural celestial body orbiting a planet. So its a moon until it breaks free of orbit and then becomes a rogue planet.

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There isnt a moon. A planet is a body that hasnt undergone nuclear fusion but is big enough to maintain a spherical shape. This way the definition now includes planets in other solar systems or without orbits.

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I didn't read the full text either. I like the new definition not going by the orbits because orbits could change. We could still describe planets that orbit other planets as a moon planet to the the planet that they orbit. It seems to be a plausible change of definition that makes sense and Pluto would be a planet again, yeah!

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I think they need to find a middle ground on this, for example I consider Pluto to be a planet. It's round and it even has smaller bodies orbiting it (4 or 5 satellites). For me it's a planet regardless of what else is in it's orbital neighbourhood (Kuiper belt objects).

I think any round body that is orbiting another body much bigger than it should be considered a dwarf planet (so this includes the moon and all those round objects orbiting the gas giants etc). On the other hand smaller objects like Phobos and Deimos orbiting mars which are not round should be called satellites.
For example there are satellites (which should be called dwarf planets) bigger than mercury but mercury is on it's own (not orbiting a larger body) and orbiting the sun and it's massive enough to be round so it's a planet.
On the other hand Ganymede & Titan are bigger than mercury but they are in orbit around larger bodies (in this case Gas Giants) so calling them a planet even though they are bigger than mercury seems wrong, I would be happy to call them dwarf planets instead of satellites (including our moon). This way we go back to 9 planets in the solar system (as it should be).

One last note on this is the prospect of this

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2 hours ago, Nnicolette said:

There isnt a moon. A planet is a body that hasnt undergone nuclear fusion but is big enough to maintain a spherical shape. This way the definition now includes planets in other solar systems or without orbits.

all you have to do is replace the word sun with the word star.  everything else falls into place.

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I think they have to make some kind of distinction between larger and smaller round bodies. Where do you for example otherwise draw the line when you teach school children about the planets. You can't have a school test question like "Write the names of the 112 planets of the solar system and some characteristics of each planet.".

Edited by fred_mc
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If the new planetary numbers stick, I hope they get "real" names and not something like Sol100.  We have plenty of Gods and cartoon characters left to name te new planets after.

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Interesting how this would change the way we talk about our solar system  From the paper:

 

Implicitly using the geophysical planet definition in context is easy. Teachers may introduce new moon planets to their students

with phrases such as, “In the 2020s, NASA will send a spacecraft to study the planet Europa,

which orbits around Jupiter as one of its many moons.”

 

The paper also addresses the problem this would cause with  kids memorizing the planets:

 

Certainly 110 planets is more than students should be expected to memorize, and indeed they ought not.

Instead, students should learn only a few (9? 12? 25?) planets of interest. For an analogy, there are 88

official constellations and ~94 naturally occurring elements, yet most people are content to learn only a few.

So it should be with planets. Understanding the natural organization of the Solar System is much more

informative than rote memorization. Teaching the zones of the Solar System from the Sun outward and

the types of planets and small bodies in each is perhaps the best approach: The zone closest to the Sun

consists of rocky planets; the middle zone consists of gaseous, rocky, and icy planets; and the third zone

consists of icy planets. All zones also have small, non-round, asteroidal/cometary bodies

 

Paper is only a page an a half long http://www.hou.usra.edu/meetings/lpsc2017/pdf/1448.pdf

Edited by Merc14
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Perhaps there could be primary planets and secondary planets. Primary planets orbit the Sun, and secondary planets orbit primary planets. Life was much simpler when I was young!

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When I was young I was taught the mnemonic Mother Very Thoughtfully Made A Jam Sandwich Under No Protest (Mercury Venus Terra/Earth Mars Asteroid Belt Jupiter Saturn Uranus Neptune Protest).

It was a great way to learn the order of the planets and also where the asteroid belt lays.

I motion that planets orbit stars and moons orbit planets, re-promote Pluto to planet status, then the mnemonic fits again and as a bonus we have 9 planets, which means we can call the next discovered planet as Planet X (X being romaneral for 10) which sounds cool!

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1 hour ago, EBE Hybrid said:

re-promote Pluto to planet status, then the mnemonic fits again and as a bonus we have 9 planets, which means we can call the next discovered planet as Planet X (X being romaneral for 10) which sounds cool!

There is no sane definition of a planet which can include Pluto but exclude the rest of the dwarf planets.You can have 8 planets in the solar system or you can have dozens (potentially hundreds). Nine is not an option*.

*Edited to add:

Unless of course the hypothetical Planet 9 is proven to exist,in which case 9 will be an option, but only if you don't include Pluto. What ever definition of a planet is finally settled on you are going to have to learn a new mnemonic.

Edited by Waspie_Dwarf
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Oh buggar, my brain is so full of old stuff I'm finding it tricky to fit any new mnemonics in.

However I really should learn a new mnemonic for resistor colour coding (as in electronic), that was near the mark in the 80's and to speak it aloud would probably be classed a hate crime now!

Edited by EBE Hybrid
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I'm glad I will never have to name them all on a test. The change seems to make sense though.

Edited by Four Winds
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8 hours ago, Four Winds said:

I'm glad I will never have to name them all on a test. The change seems to make sense though.

It makes no sense!  Everyone knows a moon is a satellite orbiting a planet. 

It so happens there exist round moons too. There is nothing wrong with calling them what they are.  

If a planet was orbiting it's moon then the moon would be the planet and vice versa.  But they don't.  There is an obvious distinction, so let it be.

That is not to say in other solar systems twin planets, even triplets, might exist, perhaps even sharing the same atmospheres.  

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21 hours ago, White Unicorn said:

I didn't read the full text either. I like the new definition not going by the orbits because orbits could change. We could still describe planets that orbit other planets as a moon planet to the the planet that they orbit. It seems to be a plausible change of definition that makes sense and Pluto would be a planet again, yeah!

 

20 hours ago, WelshRed said:

I think they need to find a middle ground on this, for example I consider Pluto to be a planet. It's round and it even has smaller bodies orbiting it (4 or 5 satellites). For me it's a planet regardless of what else is in it's orbital neighbourhood (Kuiper belt objects).

No. Just no. We shouldn't change definitions just to comply with people's bias and nostalgia. It's counterproductive and the opposite of what science stands for. Pluto isn't a planet any more than other dwarf planets, so it shouldn't be considered one by any sensible definition.

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I find the new definition an interesting compromise that reflects the history of planetary discovery within our solar system while providing opportunity for broad application beyond our solar system as new discoveries are made.

Edited by highdesert50
reason for edit: words dropped when posted
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9 minutes ago, highdesert50 said:

I find the new definition an interesting compromise that reflects the history of planetary discovery within our solar system while providing opportunity for broad application beyond our solar system as new discoveries are made.

We'll have to see what the IAU says about it.

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