A discussion on "officially called a planet"

In summary, the conversation discusses the potential discovery of a TNO called "planet 9" that does not meet the current criteria for being classified as a planet by the IAU. The speakers suggest that it may need a new term or redefinition of what a "planet" is. They also consider whether its eccentric orbit and inability to clear debris would disqualify it from being classified as a planet, despite its large size.
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fizzy
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Forking a subject that was in risk of hi-jacking anther thread here.

If the hypothetical TNO "planet 9" is detected , it would not fit the IAU's current criteria of being a planet. What would it be ?

For the sake of discussion let's assume 10 Me and estimated likely distance and orbital period.

Would it fit an existing category or would it require a new term or another redefinition of what a "planet" is?
 
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  • #2
A really big TNO(Trans-Neptunian Object)?
 
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  • #3
Current definition:
  • orbits the sun
  • has sufficient mass to be round, or nearly round
  • is not a satellite (moon) of another object
  • has removed debris and small objects from the area around its orbit
https://www.space.com/25986-planet-definition.html

A more specific take on the 4th criteria is that it has a mass greater than the combined mass of all objects in a similar orbit.

Given the distance, I think such objects tend to have eccentric orbits and trouble clearing them. Thus I don't think they can be classified as planets.
 
  • #4
Yes , the orbit clearing thing is what caught Plluto out, but a 10Me it can't be called a dwarf planet; neither is it a rogue if it is orbiting.

It's planet sized but not a planet. Will we need to move the goalposts again?
 
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1. What is the definition of a planet?

A planet is a celestial body that orbits around a star, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and has cleared the neighborhood around its orbit.

2. Why did Pluto lose its status as a planet?

In 2006, the International Astronomical Union (IAU) defined a planet as a celestial body that meets three criteria: it orbits around the sun, has enough mass to pull itself into a nearly spherical shape, and has cleared the neighborhood around its orbit. Pluto, however, did not meet the third criteria as it is located in a region of space known as the Kuiper Belt, which contains many other objects that have not "cleared the neighborhood" around their orbits. Therefore, Pluto was reclassified as a "dwarf planet" rather than a planet.

3. How many planets are in our solar system?

As of now, our solar system has eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. However, there is ongoing debate and discovery of potential new planets beyond Neptune, so this number may change in the future.

4. Can a planet have multiple moons?

Yes, a planet can have multiple moons. For example, Jupiter has the most moons in our solar system with 79 known moons, while Earth has just one moon.

5. How do scientists classify planets?

Scientists classify planets based on their physical characteristics, such as size, mass, and composition. They also consider a planet's orbit and its relationship to other objects in its vicinity. With advancements in technology and new discoveries, the classification of planets may change over time.

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