Planet Definitions
xkcd.com

Under the ‘has cleared its orbital neighborhood’ and ‘fuses hydrogen into helium’ definitions, thanks to human activities Earth technically no longer qualifies as a planet but DOES count as a star.

https://explainxkcd.com/3063/

  • Cosmic Cleric@lemmy.worldEnglish
    0·
    28 days ago

    I personally don’t think they can be counted as skies and oceans etc. anymore when they’re being mixed in with multi-thousand-degree hydrogen/helium plasma.

    So Mars never had oceans? Or an atmosphere?

    So Saturn’s moon Titan doesn’t have lakes? Or an atmosphere?

    What happens if a body is found in the Oort Cloud that has an internal heat source so that it has a internal ocean like Europa? It’s it still not a planet because the space around it is busy?

    This comment is licensed under CC BY-NC-SA 4.0

    • Magiilaro@feddit.orgEnglish
      0·
      28 days ago

      One of the idea with “has the space around it cleared” is that the body has the right size and gravitational pull. The theoretical object in the Oort Cloud would relative fast clear the space around himself if it had the size to have a stable and long living internal heat source (that would either need lots of decaying nuclear material or would need to be at least about earth size to have enough stored energy to have a molten core).

      So if you put earth into the Oort Cloud it would still be a planet, because we know that earth has the potential to clean it’s neighborhood. Not that our definition would be relevant, because Earth in the Oort Cloud would be a lifeless rock very fast, with nobody left to care about definitions.

      • Cosmic Cleric@lemmy.worldEnglish
        0·
        28 days ago

        So if you put earth into the Oort Cloud it would still be a planet, because we know that earth has the potential to clean it’s neighborhood.

        Would it be a non-planet for the millions of years it would take to clear its orbit?

        Does Earth’s body/features magically change somehow for the duration of the clearing process, so that it doesn’t resemble a planet?

        The point is that using external criteria to identify what an internal thing is is not logical, or scientific.

        The theoretical object in the Oort Cloud would relative fast clear the space around himself if it had the size to have a stable and long living internal heat source.

        You don’t know that, especially with the size of the Oort Cloud, and the size of the orbit to clear. And the rules for how much clearance has to be done is very arbitrary.

        Also bodies can be small and have a decaying heat source that’ll last many millions of years, or renewing heat source via tidal interactions. It’s not necessarily a size thing.

        This comment is licensed under CC BY-NC-SA 4.0