IAU Redefines the Solar System: 12 Planets, Countless Possibilities

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SUMMARY

The International Astronomical Union (IAU) has redefined the Solar System to include 12 planets, introducing Xena (2003 UB313) as the most distant planet and Charon as part of a double planet system with Pluto. Ceres, previously classified as an asteroid, is now recognized as the smallest planet. The new definition states that a planet must be a celestial body with sufficient mass for hydrostatic equilibrium, orbiting a star, and not a satellite of another planet. This change may lead to a rapid increase in the number of recognized planets, potentially reaching hundreds or thousands in the future.

PREREQUISITES
  • Understanding of celestial mechanics and hydrostatic equilibrium
  • Familiarity with the classification of astronomical bodies
  • Knowledge of the Kuiper Belt and Trans-Neptunian Objects
  • Awareness of the historical context of Pluto's classification
NEXT STEPS
  • Research the implications of the new IAU definition of a planet
  • Explore the characteristics of Trans-Neptunian Objects and their classification
  • Study the differences between dwarf planets and classical planets
  • Investigate the ongoing debates surrounding Pluto's status and the concept of "plutons"
USEFUL FOR

Astronomers, astrophysicists, educators, and anyone interested in the evolving definitions and classifications within planetary science.

  • #31
"My Very Educated Mother Just Showed Us Nine Planets", the famous mnemonic to remember the names of the nine planets when we were kids viz. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto.
I wonder what kind new mnemonic has to be invented with the recent developments in the order of planets :biggrin: .
 
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  • #32
Yeah, that is kind of a cop-out, isn't it? I mean, by that definition, Neptune should also be downgraded, because it hasn't cleared Pluto out of its orbit.
 
  • #33
It seems to me they picked a definition where they can call anything a planet or a non-planet, depending on how they "feel" about the object. Really, this whole process was a complete waste of time, and the definition they came up with is downright pathetic.
 
  • #34
Come to think of it, since there are still thousands of NEO's, we don't live on a planet, do we?
 
  • #35
How could there be 12 when they just announced Pluto isn't a planet?
 
  • #36
Line said:
How could there be 12 when they just announced Pluto isn't a planet?

They initially proposed 12 planets, the proposal is then rejected and ended up with demoting pluto instead.
 
  • #37
I'm happy with everything the IAU has done, except "dwarf planets." While Pluto was a planet it had "double status" as a planet and a Kuiper belt object; now it's simply a "dwarf planet" and nothing else. Pluto and Eris (Xena) are clearly just very big Kuiper belt objects, and while I'm happy with the dwarf-planet classification to make them special (Pluto and Eris are special because they're so large and rounded) I think they should also have dual status as dwarf planets and KBOs. They are clearly KBOs and should be recognised as such.
Ceres is an asteroid. Don't tell me it's not. OK, it's special, it deserves to be classed as a dwarf planet because it's large and round, yeah yeah. But... it's clearly an asteroid. Just a big one. How can you possibly say it isn't?
I'd be happy with 8 or 12 planets, as long as Pluto/Eris were recognised as KBOs as well as (dwarf) planets and Ceres was an asteroid as well as a (dwarf) planet.
 

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