<p>There is no clear separation in mass between planets found orbiting stars and &quot;free-floating&quot; planetary-mass objects (although inferring the mass of the latter from their observable properties is highly age- and model-dependent).</p>
<p>Some &quot;free-floating planets&quot; may have been ejected from their birth systems. This is a hazard that is theoretically predicted in any dense, clustered phase of the star forming environment. Others may have been born as isolated objects and simply represent the low-mass tail of the initial mass function.</p>
<p>Note, that I would be one of those <em>against</em> labelling something as a &quot;planet&quot; just because its mass is below the somewhat arbitrary threshold of 13 Jupiter masses (the deuterium-burning threshold). I think a low-mass lump of gas that contracts in isolation is just a low-mass brown dwarf. Others disagree.</p>

CC BY-SA 4.0
2023-04-11T17:40:41.923Z
Dust is also found in interstellar space.  Thus an object forming in interstellar space might contain a lot of dust and solid matter, which might make it more like a planet than a mass of gas.   Any partially solid object in interstellar space which is massive enough to become a spheroid through its gravity is a  planetary mass object or planemo.  So it seems perfectly proper to speak of rogue planemos in inteterstellar space.
M. A. Golding
CC BY-SA 4.0
2023-04-11T19:41:38.470Z
@M.A.Golding Dust is 1% of the mass in interstellar gas. A planetary-mass object forming in isolation would have a minimal solid content and could not form via the "core-accretion" scenario thought to be responsible for the giant planets in our Solar System. Another reason not to call such objects planets.
ProfRob
CC BY-SA 4.0
2023-04-11T06:12:56.090Z
2023-04-11T06:12:56.090Z
ProfRob
<p>The April 2, 2023 Inverse article <a href="https://www.inverse.com/science/rogue-planets" rel="noreferrer">9 Years Ago, Astronomers Found Two Rogue Planets — But They Didn’t Realize It Until Now</a> says:</p>
<blockquote>
<p>Planets are typically part of a planetary system and are gravitationally bound to their star, or stars in the case of a binary star. Planets can migrate toward and away from their star when conditions are right, but they stay bound to the star, even if separated by a vast distance. But sometimes, a planet is kicked out of its system due to a supernova explosion, a stellar interloper, or some other event. <strong>And in some cases, a planet can form on its own outside of any solar system.</strong> These are rogue planets or free-floating planets (FFPs.)</p>
</blockquote>
<p><strong>Question:</strong> What are the cases in which free floating planets (FFP's) can form on their own, outside of any solar system?</p>

CC BY-SA 4.0
2023-04-10T08:56:30.753Z
Probably talking about [Sub brown dwarf](https://en.wikipedia.org/wiki/Sub-brown_dwarf) There is, it seems some disagreement about nomenclature, with some calling such objects "rogue planets" and others not.
James K
<astrophysics><planetary-formation><planetary-science><rogue-planet>
"And in some cases, a (free floating) planet (FFP) can form on its own outside of any solar system." Cool! But what are those cases?
uhoh
# "And in some cases, a (free floating) planet (FFP) can form on its own outside of any solar system." Cool! But what are those cases?

(Asked by: username_0 on 2023-04-10)

The April 2, 2023 Inverse article [9 Years Ago, Astronomers Found Two Rogue Planets — But They Didn’t Realize It Until Now](https://www.inverse.com/science/rogue-planets) says:

> Planets are typically part of a planetary system and are gravitationally bound to their star, or stars in the case of a binary star. Planets can migrate toward and away from their star when conditions are right, but they stay bound to the star, even if separated by a vast distance. But sometimes, a planet is kicked out of its system due to a supernova explosion, a stellar interloper, or some other event. **And in some cases, a planet can form on its own outside of any solar system.** These are rogue planets or free-floating planets (FFPs.)

**Question:** What are the cases in which free floating planets (FFP's) can form on their own, outside of any solar system?

**Tags:** astrophysics, planetary-formation, planetary-science, rogue-planet

> **Comments:**
> **username_1**: Probably talking about [Sub brown dwarf](https://en.wikipedia.org/wiki/Sub-brown_dwarf) There is, it seems some disagreement about nomenclature, with some calling such objects "rogue planets" and others not.  

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## 1 answers

### Answer by username_2 on 2023-04-11. Score: 3

There is no clear separation in mass between planets found orbiting stars and "free-floating" planetary-mass objects (although inferring the mass of the latter from their observable properties is highly age- and model-dependent).

Some "free-floating planets" may have been ejected from their birth systems. This is a hazard that is theoretically predicted in any dense, clustered phase of the star forming environment. Others may have been born as isolated objects and simply represent the low-mass tail of the initial mass function.

Note, that I would be one of those *against* labelling something as a "planet" just because its mass is below the somewhat arbitrary threshold of 13 Jupiter masses (the deuterium-burning threshold). I think a low-mass lump of gas that contracts in isolation is just a low-mass brown dwarf. Others disagree.

> **Comments:**
> **username_3**: Dust is also found in interstellar space.  Thus an object forming in interstellar space might contain a lot of dust and solid matter, which might make it more like a planet than a mass of gas.   Any partially solid object in interstellar space which is massive enough to become a spheroid through its gravity is a  planetary mass object or planemo.  So it seems perfectly proper to speak of rogue planemos in inteterstellar space.  
> **username_2**: @username_3 Dust is 1% of the mass in interstellar gas. A planetary-mass object forming in isolation would have a minimal solid content and could not form via the "core-accretion" scenario thought to be responsible for the giant planets in our Solar System. Another reason not to call such objects planets.  

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