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]