Pluto Planet Status

[Voyager275]

Since 2006 people have disagreed with the IAU decision for Plutos reclassification. After New Horizons flew by the dwarf planet, the debate started again. From New Horizons mission scientists to several astronomers, and even 4,100 petition signatures, it seems people want Pluto as a planet again. What do you think we should call the far away object? Planet or not?

[Bill Phil]

How about all Pluto, Ceres, and all the other similar ones are planets, too. Then we'd have the 8 major planets and a large number of minor planets.

[UmbralRaptor]

Pluto is just as much a planet (or not) as Ceres, Eris, Haumea, and Makemake. (and practically speaking, the IAU will need to add several more bodies to the official dwarf planet list in the future).

[SAI Peregrinus]

Even if it's a planet, it's a double-planet with Charon, since they orbit a common barycenter outside both bodies. So it would be Pluto-Charon. Pluto alone can't be a planet.

[Asharad]

Even if it's a planet, it's a double-planet with Charon, since they orbit a common barycenter outside both bodies. So it would be Pluto-Charon. Pluto alone can't be a planet.

Someday, the Earth-Moon barycenter will be in space. When that day comes will Earth cease to be a planet?

[NFUN]

Someday, the Earth-Moon barycenter will be in space. When that day comes will Earth cease to be a planet?

That day Earth will be a binary planet.

[vger]

Someday, the Earth-Moon barycenter will be in space. When that day comes will Earth cease to be a planet?

Planethood is becoming far too complicated. It was so much easier in the old days. You just got your certificate and that was it. Now planets and their moons actually have to do... work... and check in with the IAU every year to ensure they're still entitled to the benefits.

Sign of the times, I tell ya.

[Sampa]

(Don't,join the debate...don't join the debate...don't join the debate) pluto is a,planet in my book!

[Xannari Ferrows]

By original definition, Planet comes from the greek "planan", which means wanderer. Since Pluto is a wanderer, being that it moves differently in the sky from the stars, it is a planet.

[RainDreamer]

Reminds me of a xkcd comic that proposed naming an exoplanet Pluto, so this debate gets even more confusing.

[fredinno]

Wait, what? How would that ever happen?

[Shpaget]

Even if it's a planet, it's a double-planet with Charon, since they orbit a common barycenter outside both bodies. So it would be Pluto-Charon. Pluto alone can't be a planet.

That day Earth will be a binary planet.

Does that mean our Sun is a binary star, since Sun Jupiter barycenter is outside the Sun?

[fredinno]

The Jupiter-Sun barycenter is not outside the boundary of the Sun.

[Brotoro]

Sure it is.

(It's at 1.07 solar radii)

[Hagen von Tronje]

I've never understood why this debate even exists. A rose by any other name, folks. The sun did not become less bright when it was declared a G-type main sequence star rather than THE sun. Science marches on and new terms and classifications have to accomodate that.

Especially baffling because there's no evidence that astronomers or anyone else has lost interest in it due to the change in terminology.

We didn't "lose" a planet. We "gained" a whole new class of celestial bodies orbiting our sun, and astronomers saw fit to give expression to their secret love of Lovecraft and GWAR by naming them after death gods. How do you call any of that a loss?

Edited August 24, 2015 by Hagen von Tronje

[Frida Space]

By original definition, Planet comes from the greek "planan", which means wanderer. Since Pluto is a wanderer, being that it moves differently in the sky from the stars, it is a planet.

That's just the worst definition ever, there would be millions of planets just in our solar system. Plus, there is no such thing as a "uniform star motion". All stars move differently from each other, they all have their own proper motion. Should, say, Barnard's star be considered a planet too then, as it "wanders around"?

[Dooz]

The Jupiter-Sun barycenter is not outside the boundary of the Sun.

Diagram from NASA

[YNM]

There's also an exoplanet named Pluto, I don't know which one you're talking about.

Joke aside, this kind of debate now kind of gets very old. We should drop the word "planet" alltogether.

[Sampa]

what is a barycenter anyway?

[peadar1987]

what is a barycenter anyway?

Averaged centre of mass. If you take the earth and the moon for example, its mass is about 1% that of the earth. The barycentre of the earth-moon system is about 1% of the way from the centre of the earth to the centre of the moon. This is still well inside earth's surface, but if the moon was more massive, or further away, this point would be outside the surface of the earth.

Celestial bodies will orbit the barycentre of a system.

[mellojoe]

The Pluto debate must always include Ceres, that giant asteroid thing between Mars and Jupiter. Why? Because Ceres was originally considered a planet. It was predicted to exist in the gap between Mars and Jupiter. All the planets had pretty evenly spaced orbits, and then a huge gap, and then Jupiter, Neptune and even Uranus. That famous guy Kepler noticed this odd gap way back when. Then Ceres was discovered. Aha! The missing planet. Ceres was a "planet" for over 50 years.

The more we learned, the more we realized that a single category system was not sufficient. Science is about finding the truth, and that often means our opinions change as we learn more. What we know today might be proved incorrect as more information comes in. Let us not forget that it was in 1900 when Albert Michelson stated that an eminent physicist declared that we know everything, and "that the future truths of physical science are to be looked for in the sixth place of decimals." Meaning, we knew it all, we just would get better measurements. It was less than 7 years later when Einstein proposed his theory of Relativity and changed everything we thought we knew.

If we call Pluto a planet, then we must also call Ceres a planet. And then we would end up including much of the objects from the Asteroid Belt, similarly to how we would have to include everything from the Kuiper Belt.

Think about it another way: If the Earth humans grew up on was part of a binary planetoid system, would that change our definition of planet? Would Jupiter be considered a planet if it was the only gas giant? What if Earth was part of a belt system of multiple objects? Our definition of "planet" is based on "what behaves similar to Earth". Or at least it did, until the 2006 consortium laid down official rules. What we know today may change in the future.

Don't be scared of change in the scientific community, it just means we learned something new.

[vger]

We didn't "lose" a planet.

What I find particularly odd is the very next decision made AFTER downgrading Pluto, was to say that Dwarf Planets aren't any kind of Planet.

Why a name like "Dwarf Planet" when it isn't even recognized as a sub-class of a Planet?

[Shpaget]

Why are some of you guys so bothered by the label we put on things? It has absolutely no effect on the thing that is labeled. Pluto is exactly same, being called a planet or not.

For language to work, there have to be some artificial limits and boundaries that humans agree on. Those boundaries do not necessarily exist in nature so, for the purposes of language, we have to group objects into certain categories, even though there is not necessarily a hard limit between different categories.

[vger]

Why are some of you guys so bothered by the label we put on things? It has absolutely no effect on the thing that is labeled. Pluto is exactly same, being called a planet or not.

Heh... have you been watching the news lately? Try telling someone, "Don't worry about it - you're still you, no matter what anybody calls you," and see how long it takes before you get digitally burned at the stake for some kind of evil. Words and labels have become the center of pretty much everything.

Edited August 24, 2015 by vger

[NFUN]

Does that mean our Sun is a binary star, since Sun Jupiter barycenter is outside the Sun?

Is Jupiter a star?

In any case, a binary star system is different in a few ways than binary planets. A binary planet system that is caused more because of a medium sized, distant moon would be less common than the same situation involving stars, such as the case with Jupiter and the Sun. The scales involve make the former less likely because such a situation would be, in the long term, less stable than the latter.

Edited August 24, 2015 by NFUN