The Pluto problem: Is it time to rethink our definition of a planet?

[Admin]

In 2006, the International Astronomical Union (IAU) famously demoted Pluto to a dwarf planet. Things have been a bit of a mess since then — so is it time to redefine the planet?

The Pluto problem: Is it time to rethink our definition of a planet? : Read more

 

[geir]

Roundness and orbit clearance are potentially dynamic and definitely subject to interpretation (is Vesta 'round enough'?). Mass, less so . Pick a mass and stick with it. I'd say 0.001 Earths ~6x10^21 kg.

 

[Helio]

“Eight is enough.”

Physics can step in and clarify the gray areas.

Jean-Luc Margot produced a paper applying physics to orbit clearing which is a function of mass and distance. It’s not overly complicated. I think this solves the problem for exoplanets , as well.

Besides adding at least four more potential “planets” to the list schools need to teach for memorization, we need to consider that distant round bodies could be found in the hundreds once powerful surveys reach hundreds of AUs where such objects are too feeble for today’s scopes. Then there’s the possibility of the distant Oort objects adding to the number.

The Sun and Moon, btw, were also once called planets.

If we chose to debate this, I propose we first change the color use of “yellow” for a non-yellow Sun.

 

[geir]

“Eight is enough.”

Physics can step in and clarify the gray areas.

Jean-Luc Margot produced a paper applying physics to orbit clearing which is a function of mass and distance. It’s not overly complicated. I think this solves the problem for exoplanets , as well.

Besides adding at least four more potential “planets” to the list schools need to teach for memorization, we need to consider that distant round bodies could be found in the hundreds once powerful surveys reach hundreds of AUs where such objects are too feeble for today’s scopes. Then there’s the possibility of the distant Oort objects adding to the number.

The Sun and Moon, btw, were also once called planets.

If we chose to debate this, I propose we first change the color use of “yellow” for a non-yellow Sun.

Then make the mass cut-off bigger: 0.01 Earths. Kids have to deal with the alphabet and the elements... I think they can count past the number of fingers...
By the 'clear the orbit criteria', Earth wasn't even a planet until after bits of Theia became a moon (planet-sized moon). It's transitory and situational.

 

[Helio]

Then make the mass cut-off bigger: 0.01 Earths. Kids have to deal with the alphabet and the elements... I think they can count past the number of fingers...

Using mass would be okay, perhaps, if it could be determined. Astronomers normally can’t determine mass but they can approximate radius. However, even the Margot method must estimate mass, admittedly.

There is a fair chance we will have dozens of dwarf planets discovered in the next couple of decades.

By the 'clear the orbit criteria', Earth wasn't even a planet until after bits of Theia became a moon (planet-sized moon). It's transitory and situational.

But physics doesn’t care since the only three variables are required.

IIRC, the Margot method assumes 1 billion years of clearing time, so Theia events aren’t an issue.

[on iPhone at airport]

 

[Witchy]

“Eight is enough.”

Physics can step in and clarify the gray areas.

Jean-Luc Margot produced a paper applying physics to orbit clearing which is a function of mass and distance. It’s not overly complicated. I think this solves the problem for exoplanets , as well.

Besides adding at least four more potential “planets” to the list schools need to teach for memorization, we need to consider that distant round bodies could be found in the hundreds once powerful surveys reach hundreds of AUs where such objects are too feeble for today’s scopes. Then there’s the possibility of the distant Oort objects adding to the number.

The Sun and Moon, btw, were also once called planets.

If we chose to debate this, I propose we first change the color use of “yellow” for a non-yellow Sun.

Memorization is an outdated method of teaching the solar system. Kids don't need to memorize a list of names. They can learn the different subtypes of planets and their defining characteristics. We don't artificially limit the number of stars or galaxies for the purpose of memorization and shouldn't do that with planets either. If our solar system has 100+ planets, then that is what it has.

 

[Witchy]

There is more than one planet definition currently in use. What this article doesn't say is that only four percent of the IAU voted in 2006, and most who voted weren't planetary scientists but other types of astronomers. An equal number of planetary scientists rejected their definition back then and to this day instead prefer the geophysical planet definition, which does not require orbit clearing. Dr. Phil Metzger published a study on the use of the term "planet" in scientific journals and found that most article writers used the geophysical definition rather than the IAU definition. According to the geophysical definition, if an object is large enough and massive enough to be rounded by its own gravity, it is a planet. Dwarf planets are a subclass of planets. This makes both Ceres and Pluto planets of the dwarf planet subcategory and not "minor planets," a term that is synonymous with asteroids and comets.

 

[Mustellus]

Planets are 'wanderers'..... nope
Planets orbit the sun ... but asteroids and comets orbit the sun, but aren't planets
Planets clear out their orbit.... no, only ones where the orbital period is 'short' . Pluto and Eris will never qualify. And grins.. .if Planet X exists.. it can't be a planet by this definition.
Me.. I'm going to go with the geologists. If its round, has a core / mantle / crust structure,.. if it has a 'geology' its a planet. Our solar system has about 50 of'm.
And allow me a point of radicalism: Gas giant 'planets' are failed stars.

 

[bolide]

A Type I Planet:

1. Is not & never was a star
2. Orbits a star
3. Is massive enough to be within x% of a sphere
4. Constitutes more than 50% of the mass in its orbit.

Type II, III, etc planets can meet relaxed versions of these criteria.