Rogue planet

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Rogue planet

Post by Ryag Han on 27th December 2009, 7:27 am

A Rogue planet is a planetary body that is no longer bound to a star,and is now drifting in space by its own.
It is a pretty interesting idea, but how could such an object form.
There might be some options like trowed out of the system by a larger body with a slingshot effect,
by the star itself when it become a supernova (if it survived) or simply a decaying orbit that toke it out
of the stars reach.
Cha 110913-773444might be a brown dwarf or a rouge planet,but scientist don't know how to classify it.
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Re: Rogue planet

Post by Sirius_Alpha on 27th December 2009, 8:21 am

Ryag Han wrote:There might be some options like trowed out of the system by a larger body with a slingshot effect,
by the star itself when it become a supernova (if it survived) or simply a decaying orbit that toke it out

The first is likely the cause of most rogue planets.
The second will result in the orbits of the planets suddenly becoming more eccentric, which will then lead to the first happening.
The third probably does not occur. Assuming a two body system, a planet will remain bound to the star for any reasonable mass that the star has throughout its lifetime.

If I recall correctly, objects like Cha 110913-773444 are likely to have formed by themselves in interstellar space out of a collapsing low-mass cloud.

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Re: Rogue planet

Post by Lazarus on 27th December 2009, 9:49 am

There are definitely indications that the stellar formation process continues down at planetary masses, below the deuterium fusion limit. Cha 110913-773444 probably was not formed in the same way as planets are, and thus there is a good case for calling it a brown dwarf.

Such formation-based definitions are on the other hand rather harder to work with on an observational, case-by-case basis, even though they definitely have utility in describing populations and systems of objects. The deuterium fusion limit provides a relatively easy-to-determine criterion for the division of planets and brown dwarfs, so there is also a good case for calling it a planet.

Personally I find the argument calling it a brown dwarf more persuasive, but certainly the matter is not settled in the astronomical community.
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Re: Rogue planet

Post by Sirius_Alpha on 27th December 2009, 11:24 am

But deuterium fusion, as I understand it, doesn't have a specific cut-off limit. Brand new planetary mass objects host deuterium fusion for a time and then as they cool that shuts off. And even then it depends on metallicity of the object.

At what mass is a gas giant able to fuse deuterium? Even just one atom of deuterium.

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Re: Rogue planet

Post by TheoA on 29th December 2009, 7:34 pm

Also the D-D fusion is kicked of by gravitational heating, which can vary substantially depending on the disk formation process.

Which means some > 13J mass object may never burn Deuterium.

So mass and Temperature matters.

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