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Comment by jessriedel | Hacker News Reader

> My understanding is that smaller rouge plants do not form in isolation and are always the product of ejection.

Wikipedia says "Rogue planets may originate from planetary systems in which they are formed and later ejected, or they can also form on their own, outside a planetary system."

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The ones "forming on their own" would be essentially brown dwarfs. As myself and others have said, the line is fuzzy. However, to form on their own there needs to be sufficient density for them to coalesce. It is not a hard limit, but tends to mean only objects larger than about 10 Jupiter masses.

No. That’s not what wikipedia says, and I feel confident asserting that an Earth-mass object forming on its own would not be considered a brown dwarf by the vast majority of astronomers. (Maybe it would also not be considered a “planet”, due to some Pluto-adjacent technicalities, but then what do people call it? I’m betting they use “rogue planet” in practice.)

I think you are missing the size distinction and range for rogue planets, which I specifically highlight.

Claims about self formation pertain to rouge planets as a class, which includes brown dwarfs. That does not mean an earth mass object IS a brown dwarf.

If you want to want to focus on Wikipedia text, it also says:

>Pre-JWST observations have shown that objects below 3-5 MJ are unlikely to form on their own.[4] Observations in 2023 in the Trapezium Cluster with JWST have shown that objects as massive as 0.6 MJ might form on their own, not requiring a steep cut-off mass[1]

Those limits are ~1,000 earth masses and ~200 earth masses, respectively

https://en.wikipedia.org/wiki/Rogue_planet#Formation_like_a_...

No, an Earth-mass object forming on its own would not be considered a brown dwarf, but an Earth-mass object is incredibly unlikely to form on its own. An object that small will have almost certainly been formed in an accretion disk and been ejected.

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