Should Pluto be a planet again?

OK, so the current IAU definition of a planet states:

(1) A planet 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.

(2) A dwarf planet 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, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".

So, unless they change the definition of 1(c), then Pluto remains a dwarf planet.

As I understand it, the argument for redefinition of Pluto as a planet comes from a debate at he Harvard-Smithsonian Centre for Astrophysics a few weeks ago. It was Dimitar Sasselov, the director of Harvard’s planetary program who argued that "a planet is the smallest spherical lump of matter that formed around stars or stellar remnants ". This definition won the debate.

If this becomes the new definition, be prepared for there to be a lot more planets added to our current list of 8!

As you say Mike we can expect there to be more planets added.  Personally I think the current definition is the correct one.  The Harvard one could create confusion I believe.

...we can expect there to be more planets added

Absolutely. This isn't an argument about "let's make Pluto a planet again". It's an argument about extending the solar system to 15, perhaps 20, "planets" (perhaps thousands when we get out into the Kuiper belt).

I imagine that conversation is taking place on their fourth pint at the Kings Arms. They miss the point completely although it is a fun conversation 🙂

Please correct me where I go wrong, Brian.

Pluto was not delegated because of its size (which the conversation i think wrongly implies) but was delegated because of a new planetary definition which added that a planet must be dominant over its orbit for it to be classed as such. Pluto was considered sharing its orbit with objects from the Keiper belt, therefore delegated from being a planet to a "dwarf planet".

If I was in that conversation, I would be adding:

"Shee here, I [hiccup] think the dwarf planet definition is shhtupid. What if there were tchwo large objects, shay bigger than Marsh on the shame orbital path, we shtill call 'em dwarf planets? eh? eh? [hiccup]"

I am not fussed whether Pluto is a planet or not, although it was sad and very unromantic to see it delegated, I just want to see a better definition for a planet than "must clear its neighborhood". If a star had such a definition, then we would be stumbling on classifying binary stars. Originally, there was a diameter classification for a planet to be at least 2000 km in diameter, wasnt there? Perhaps they should have still kept that criteria in. Why not be bold and instead of losing a planet, how about having one big happy growing family and welcome the poor little (or indeed big) kittens in from the cold. Calling an object "dwarf" should have a diameter classification not a "clear neighbourhood" definition.

The criticism therefore should be directed at the definition of the classes of solar system objects, not at whether Pluto fits the definition or not because by current definition, Pluto is in its correct classification along with several other dwarf planets. I believe there are three main classes of solar objects, right? Planets, Dwarf planets and small solar system objects (such as asteroids, comets, centaurs). The definition has logic to it but its just the naming that is flawed. Perhaps instead of calling them Dwarf planets, slave planets or dependants if the point of classing them is by their "clearing the neighbourhood".

Regardless of Pluto's classification, its actually an intriguing planet. I mean its got 5 moons, man, we only got one! And its a binary planetary system too. It has an atmosphere. So whatever its classed as, its still a more special object than other minor planets.

The classifications of solar objects are actually pretty sound apart from the dwarf planet. So first add a diameter criteria to the planet definition, say 2000km (as it was before). Then keep the definition of Dwarf planet, but call class them as dependents or even belt planets. Just not dwarf because there might be bigger than earth size objects out there in the Kuiper belt or beyond that are not dominant in its orbit.

So those are my thoughts, not sure if all my facts are right though, please correct me.

Edit: Sorry I just noticed three posts by Mike and Brian that I didnt see while I wrote this one. So sorry to repeat some stuff already said.

I remember the days when Jupiter had 12 moons and Saturn had 9, so it felt like both my childhood interest in astronomy and an orange cartoon dog each took a bit of a body-blow when Pluto was downgraded from 'planet' status.

But science, knowledge and understanding have all moved on from the days of Apollo 7 so the only justification for keeping Pluto as a planet is, as Mike says, to then open the door for dozens and dozens of new 'planets' just as the moons of Jupiter and Saturn have multiplied several-fold. The mnemonic needed to remember them all will be so long it will need a derivative mnemonic to remember it.

Either that, or redefine 'planet' as we did but make Pluto an exception because of emotional connection or historical familiarity. Which isn't exactly the scientific method.

So - sorry, Pluto. Back in the doghouse.

the Kings Arms

Tej, we gotta find that pub.

The distinction I would draw between two planets sharing an orbit and a binary star is that the planets are each orbiting a common star, while the components of a binary star are orbiting a gravitational centre that lies between them.

But you make an interesting point about potentially finding really, really big 'dwarf planets'!

My round....

What if we did have 15 to 20 planets all over a sudden? Perhaps that may fuel the public imagination and indeed government fundings in space exploration. Maybe. Just posing the question. Its all very well to be matter of fact on science but public creative selling and romanticism might be good. Perhaps 2006 was a missed opportunity. To suddenly have more verified planets instead of losing one. This might have fuelled the public imagination, "oh wow, we have new planets!...Ceres, oh such a nice name...and Eris too, lovely!...and what? There are more, oh exciting!". Instead, you go up to Joe Public or a school child and ask them about Ceres or Eris, they would stare at you blankly. On the other had those new found "planets" are blooming tiny so some would also see it as "this is getting ridiculous" so that's where the diameter criteria should come in. Who knows, the mission to Pluto may not have been greenlit after the 2006 classification.

Take the Voyager missions for instance. Initially there was only funding for it to visit Jupiter...if I recall from the voyager documentaries I've seen. In comes Carl Sagan with "lets send it with a message to aliens who may cross its path" and gets children, president and musicians to record on the golden discs. He knew fully well those discs are unlikely to be picked up by aliens but through his natural ability in serenading to the public and government, he effectively sealed funding for the voyager missions full outer solar system planetary journey through romanticism and fuelled public imagination.

Just giving another possible perspective on it.

Tej, we gotta find that pub.

Its a pub in Peckham 🙂

My round….

Make mine a Ceres Extra Cold!

http://www.google.co.uk/url?sa=t&rct=j&q=&esrc ="s&source=web&cd=1&ved=0CCMQFjAA&url=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FCo-orbital_configuration&ei=C7AyVKLWE6fP7gb464CQAg&usg=AFQjCNGfx5R6bc1qKUfNHfmoNuK3tRnn1g&sig2=IVk8zOKpKPNMoE2_ZrAs5A"

http://www.google.co.uk/url?sa=t&rct=j&q=&esrc ="s&source=web&cd=2&ved=0CC4QFjAB&url=http%3A%2F%2Fwww.newscientist.com%2Farticle%2Fdn20160-two-planets-found-sharing-one-orbit.html&ei=z7AyVI7sJa-u7AbSqoHIDA&usg=AFQjCNG5BtKPumtCItykoktydBJ3VnsXow&sig2=wPCnqLAr0e9UB0QqODhjuw" .  I think the likelihood is that, as with the Earth and Theia they would eventually collide to form one planet and a moon or moons.  Tej as you can see from the first article the idea of Harvard could lead to the Trojans also being classified as planets, Where would that lead us?

https://www.youtube.com/watch?v=e98L6mftkNU

https://www.youtube.com/watch?v=e98L6mftkNU .

http://t.co/c0yn28ok3g