non-solar systems

[rogerinnh]

A recent article on the space.com site about an early solar system being detected got me to thinking about the formation of planetary systems. We always refer to them as solar systems, beacuse the planets rotate about a star. After all, without the star, we wouldn't be able to see them. But I wonder how often a planetary system might evolve from the cosmic dust but without the central, most-massive, object actually becoming a star. Could there be planetary systems in which the central object is simply another planet? In such a system would the central planet necessarily be a gas planet, or could it be a rocky planet? Is it possible that there are actually more non-solar planetary systems than solar planetary systems? Of course, detecting such systems would be mighty difficult, since we can barely even detect solar planetary systems with their huge central star illuminating its neighborhood.

 

[jatslo]

Have you heard about the invisible galaxy?

 

[nexium]

A majority of lighted systems are binary. Likely there are many "solar" sytems where negigible visable light is emitted by the center "star" = gas giant planet. A much like Earth type planet could occupy the center position, but likely this is a very rare condition.<br />White dwarfs and nuetron stars and black hole accreation discs can grow cold in less than a billion years, but may have planets.<br />Well lighted solar systems may be a small minority, but likely not a very small minority within ten light years of Earth, or we would see distant stars frequently being eclipsed by the near by unlighted bodies. Neil

 

[tony873004]

Brown Dwarfs are thought to be as numerous as stars. There's no reason they shouldn't have planets too.<br /><br />I'm not sure if a cloud can contract into something planet-sized, but if it could, then it too should have satellites.<br /><br />There can also be rouge planets that once orbited stars but were ejected from their star systems. They might be ejected with their moons.

 

[spayss]

good question.<br /><br /> A lot of this returns to definitions of 'planets', 'moons', etc. Is a pre-star a star?<br /><br />"Well lighted solar systems may be a small minority, but likely not a very small minority within ten light years of Earth, or we would see distant stars frequently being eclipsed by the near by unlighted bodies. Neil<br /><br /> I wonder about that. The planet and the star wouldn't be close to eachother so there would be no gravitational wobble or other detection. There also would never be a repetition of the event with the particular star. Stars within 10 light years are few (a dozen or so) and make up a fraction of the sky and the rogue planets would have to be in even closer. <br /><br /><br />As tony asks "There can also be rouge planets that once orbited stars but were ejected from their star systems. They might be ejected with their moons"<br /><br /> Rogue planets with orbiting moons could be orbiting the galaxy center with the rest of us. I do question, however, if we'd be able to detect these even if only a couple light years away. <br /><br /> <br /><br />