Some orphan planets never had parent stars

The standard model of star system formation posits that planets begin their existence as clouds of dust and gas orbiting a star. Over time, these bits clump together into planets. In recent years, astronomers have discovered a multitude of free-floating planets not attached to any star. In fact, there may be as many of these rogue planets are there are planets tidily orbiting their stars. It was thought that all these unattached planets must have originated as part of a star system and subsequently been ejected from their birth places. Not necessarily, say Gösta Gahm of the Stockholm University and his colleagues. Orphan planets may never have had a parent star.

Within the enormous Rosette Nebula gas cloud, cosmologists discovered hundreds of 'tiny' dark patches (less than 50 times the distance between the Sun and Neptune--this is astronomy, remember). They determined that these dark spots, dubbed ‘globulettes’, were dense clouds of gas that would one day collapse under their own weight to form planets and brown dwarfs. This is all without the benefit of a star pulling them together.

Astronomers have found that tiny, round, dark clouds called globulettes have the right characteristics to form free-floating planets. This image shows some of these tiny clouds in the Rosette Nebula, 4600 light years from Earth. 
Inset: an image taken in infrared light shows some of the globulettes in the study (marked with rings). 
Background image: Part of the Rosette Nebula.
Credit: Canada-France-Hawaii Telescope / 2003 and ESO/M. Mäkelä.

As they coalesce into planets, these globulettes are rocketing out of the Rosette Nebula at about 80,000 km/hour. This suggests that no matter where we find orphan planets, they might have originated in a nebula rather than a star system.

It's highly unlikely that any of these rogue planets would harbor life. You can't get much further from the habitable zone than by zooming around in empty space. Still, the science fiction lover in me thinks a civilization on a star-less planet would make a pretty cool story.


Gösta F. Gahm, Carina M. Persson, Minja M. Mäkelä, & Lauri K. Haikala (2013). Mass and motion of globulettes in the Rosette Nebula Astronomy & Astrophysics arXiv: 1305.2485v2.