<p>This rogue planet orbits the center of the galaxy Milk Way, (or rather, the center of mass of the system PSO J318 - rest of MW, wherever it is localised) just like the Sun and the other stars.</p>

<p>But I think the details of this orbit, that is eccentricity, period, inclination, etc are not well known.
If PSO J318.5-22 be confirmed as a Beta Pictoris association member, I guess it will have an orbit similar to the other members of this association/moving group.</p>

CC BY-SA 3.0
2014-12-30T10:28:03.670Z
What do you mean by eccentricity, period, inclination etc? This object is not orbiting another star. You are not helping the OP with their original misconception.
ProfRob
CC BY-SA 3.0
2015-02-23T14:09:36.240Z
Misconception? I mean eccentricity, period, inclination of PSO J318's orbit around the Milky Way. It could have such parameters compatible to what one expect for Beta Pictoris MG members.
Bruno Alessi
CC BY-SA 3.0
2015-02-23T17:25:43.747Z
Those terms are rarely used for Galactic orbits, certainly in the moving group field. The Beta Pic moving group is defined in terms of its U,V,W velocity. Clearly there is some sort of relationship between the two, but the latter is always what is used in the literature.
ProfRob
CC BY-SA 3.0
2014-01-30T13:41:39.333Z
2014-01-30T13:41:39.333Z
Bruno Alessi
<p>I think it is incorrect to call this object a "free floating planet", or at least it is not clear at all that it is.</p>

<p>The mass of the object is based on (a) evolutionary models of the luminosity-mass relationship and (b an assumed age for the beta Pic moving group.</p>

<p>The first point gives at least factors of two uncertainty in the claimed mass. The second point contains (in my view) a systematic error in that the authors have used an outdated age of 12Myr for the beta Pic group. It has been revised (by myself and others) to about 21-24 Myr. This would make the estimated mass about 30-50% higher and so it would be $\geq 10$ times the mass of Jupiter and could easily be at a deuterium burning mass.</p>

<p>As far as an "orbit" goes, as this object is unassociated with another star directly, but is probably part of a co-moving kinematic group (the Beta Pic moving group), it will share the orbit of that group <em>around our Galaxy</em>.</p>

CC BY-SA 3.0
2014-12-30T10:33:03.537Z
2014-12-30T10:33:03.537Z
ProfRob
<p>There is no "orbital path" detected, that's why it is a "free-floating planet". There is no radial velocity mesured, but the informations given by its kinematic location show that it belongs to the beta Pictoris group, that is a stellar group.</p>

<p>For more dirty details, have a look at the submitted paper on PSO J318.5-22:
<a href="http://arxiv.org/abs/1310.0457">http://arxiv.org/abs/1310.0457</a></p>

<p><strong>Comment:</strong>
Apart from that (the following reflects my personal opinion) the term "free-floating planet" is ill-chosen; it is clearly a very low-mass object, but since it is not orbiting around another larger object, it seems to me that the term "planet" is not pertinent. I think that it should be consider more than a "very low-mass brown-dwarf". The problem arises from IAU definition of a brown-dwarf and a exoplanet, that is probably not well-fitted for this kind of objects (and that is not really physical). You will notice, by the way, that this object is moving in a stellar group, which kind of reinforce my point.</p>

CC BY-SA 3.0
2014-01-30T19:02:54.063Z
It will probably be in an orbital path around the centre of the galaxy...
Dieudonné
CC BY-SA 3.0
2013-10-11T08:36:17.243Z
2013-10-11T09:54:24.950Z
2013-10-11T09:54:24.950Z
MBR
<p><a href="http://www.ifa.hawaii.edu/info/press-releases/LonelyPlanet/">Recent results</a> from Institute for Astronomy at the University of Hawaii at Manoa claim that there is a Jupiter-sized gas giant planet that is independent of a star about 80 light-years from Earth.</p>

<p>The press release refers to this planet as "free-floating" but I assume that it must be in some kind of predictable orbital path.  </p>

<p>What is the orbital path of this newly discovered planet?</p>

<exoplanet><gas-giants><rogue-planet>
What is the orbital path of the newly discovered star-less planet PSO J318.5-22?
DQdlM
# What is the orbital path of the newly discovered star-less planet PSO J318.5-22?

(Asked by: username_0 on 2013-10-10)

[Recent results](http://www.ifa.hawaii.edu/info/press-releases/LonelyPlanet/) from Institute for Astronomy at the University of Hawaii at Manoa claim that there is a Jupiter-sized gas giant planet that is independent of a star about 80 light-years from Earth.

The press release refers to this planet as "free-floating" but I assume that it must be in some kind of predictable orbital path.

What is the orbital path of this newly discovered planet?

**Tags:** exoplanet, gas-giants, rogue-planet


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## 3 answers

### Answer by username_3 on 2013-10-11. Score: 12 | Accepted answer

There is no "orbital path" detected, that's why it is a "free-floating planet". There is no radial velocity mesured, but the informations given by its kinematic location show that it belongs to the beta Pictoris group, that is a stellar group.

For more dirty details, have a look at the submitted paper on PSO J318.5-22:
<http://arxiv.org/abs/1310.0457>

**Comment:**
Apart from that (the following reflects my personal opinion) the term "free-floating planet" is ill-chosen; it is clearly a very low-mass object, but since it is not orbiting around another larger object, it seems to me that the term "planet" is not pertinent. I think that it should be consider more than a "very low-mass brown-dwarf". The problem arises from IAU definition of a brown-dwarf and a exoplanet, that is probably not well-fitted for this kind of objects (and that is not really physical). You will notice, by the way, that this object is moving in a stellar group, which kind of reinforce my point.

> **Comments:**
> **username_4**: It will probably be in an orbital path around the centre of the galaxy...  

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### Answer by username_1 on 2014-01-30. Score: 4

This rogue planet orbits the center of the galaxy Milk Way, (or rather, the center of mass of the system PSO J318 - rest of MW, wherever it is localised) just like the Sun and the other stars.

But I think the details of this orbit, that is eccentricity, period, inclination, etc are not well known.
If PSO J318.5-22 be confirmed as a Beta Pictoris association member, I guess it will have an orbit similar to the other members of this association/moving group.

> **Comments:**
> **username_2**: What do you mean by eccentricity, period, inclination etc? This object is not orbiting another star. You are not helping the OP with their original misconception.  
> **username_1**: Misconception? I mean eccentricity, period, inclination of PSO J318's orbit around the Milky Way. It could have such parameters compatible to what one expect for Beta Pictoris MG members.  
> **username_2**: Those terms are rarely used for Galactic orbits, certainly in the moving group field. The Beta Pic moving group is defined in terms of its U,V,W velocity. Clearly there is some sort of relationship between the two, but the latter is always what is used in the literature.  

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### Answer by username_2 on 2014-12-30. Score: 2

I think it is incorrect to call this object a "free floating planet", or at least it is not clear at all that it is.

The mass of the object is based on (a) evolutionary models of the luminosity-mass relationship and (b an assumed age for the beta Pic moving group.

The first point gives at least factors of two uncertainty in the claimed mass. The second point contains (in my view) a systematic error in that the authors have used an outdated age of 12Myr for the beta Pic group. It has been revised (by myself and others) to about 21-24 Myr. This would make the estimated mass about 30-50% higher and so it would be $\geq 10$ times the mass of Jupiter and could easily be at a deuterium burning mass.

As far as an "orbit" goes, as this object is unassociated with another star directly, but is probably part of a co-moving kinematic group (the Beta Pic moving group), it will share the orbit of that group *around our Galaxy*.


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