Are there planets not orbiting stars

[Alfred001]

I know very little about astronomy and it occurred to me that I've only ever heard of plantes orbiting stars, but I can't think of a reason why that would always be so, are there planets that are not orbiting stars?

[Strange]

Yes: https://en.wikipedia.org/wiki/Rogue_planet

[Airbrush]

Yes, rogue planets form around stars, but through gravitational interaction with other planets may get thrown out of the solar system. They estimate rogue planets may be as numerous as stars (!), if I recall correctly.

[Itoero]

Why are rogue planets not pulled back to a star because of gravitational pull?

[zapatos]

Why are rogue planets not pulled back to a star because of gravitational pull?

Because they left the orbit of the star with enough force to achieve escape velocity.

There is no reason a rogue planet cannot at some time be captured by the gravity of another star.

Edited March 15, 2017 by zapatos

[Airbrush]

The average distance between stars is so great that when a rogue planet gets thrown out of its' solar system, it is very unlikely that it will ever be captured by any other star. That is because to be captured requires very unique circumstances of trajectories, masses, and relative speeds.

 

For example they have ruled out the probability that our Moon was captured by the Earth.

Edited March 16, 2017 by Airbrush

[zapatos]

The average distance between stars is so great that when a rogue planet gets thrown out of its' solar system, it is very unlikely that it will ever be captured by any other star. That is because to be captured requires very unique circumstances of trajectories, masses, and relative speeds.

 

For example they have ruled out the probability that our Moon was captured by the Earth.

Is that right? I would think that given enough time a recapture (or collision) is inevitable.

 

Just found this...

 

 

Cambridge, MA

New research suggests that billions of stars in our galaxy have captured rogue planets that once roamed interstellar space. The nomad worlds, which were kicked out of the star systems in which they formed, occasionally find a new home with a different sun. This finding could explain the existence of some planets that orbit surprisingly far from their stars, and even the existence of a double-planet system.

"Stars trade planets just like baseball teams trade players," said Hagai Perets of the Harvard-Smithsonian Center for Astrophysics.

https://www.cfa.harvard.edu/news/2012-12

Edited March 16, 2017 by zapatos

[StringJunky]

Could planets not wander off if their star goes supernova?

Edited March 16, 2017 by StringJunky

[Janus]

Could planets not wander off if their star goes supernova?

Since a typical supernova explodes with an energy output equal to that which our Sun puts out over its entire lifetime, I doubt there would be anything left in the way of planets afterward.

[StringJunky]

Since a typical supernova explodes with an energy output equal to that which our Sun puts out over its entire lifetime, I doubt there would be anything left in the way of planets afterward.

Cheers. Wanders off as micro or nano-planets then.

[Alfred001]

"Stars trade planets just like baseball teams trade players,"

 

How does that happen?? How does a planet, once captured, leave a star's pull?

[zapatos]

"Stars trade planets just like baseball teams trade players,"

 

How does that happen?? How does a planet, once captured, leave a star's pull?

 

Stars are not the only objects in a planetary system exerting gravitational force on other planets. A near miss by a gas giant like Jupiter might eject a smaller planet.

[StringJunky]

 

Stars are not the only objects in a planetary system exerting gravitational force on other planets. A near miss by a gas giant like Jupiter might eject a smaller planet.

Wouldn't planets be at their most vulnerable going around the thin end of their elliptical orbit when acceleration, and probably momentum, is at its highest?

Edited March 17, 2017 by StringJunky

[zapatos]

Wouldn't planets be at their most vulnerable going around the thin end of their elliptical orbit when acceleration, and probably momentum, is at its highest?

 

I would think so. In addition outer planets are probably more vulnerable than inner planets as the star will have less gravitational influence on the outer planets. Planetary systems early in their life are probably also more likely to eject planets when orbits are not yet stable. And planets with eccentric orbit compared to their brethren may also be more vulnerable.