Rogue planets can form without a parent star

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Scientists call them free-floating planets — massive celestial wanderers that have broken free from the confines of their original solar system. Or perhaps not. New research suggests that these so-called rogue planets may have formed completely on their own — and that there could be billions of them.

Scientists have only recently learned about the existence of free-floating planets — planets that don’t orbit around a star.


Late last year, astronomers announced the discovery of CFBDSIRJ2149, the nearest free-floating planet that we know of. It’s located at the stone’s throw distance of 100 light-years and is somewhere between 4 to 7 times the mass of Jupiter. The free-floater is also very cool; in visible light it would be a dim, deep red color.

And it's just drifting aimlessly through space.

Until now, scientists simply assumed that these planets, of which only a few are known, originated in existing planetary systems. They just happened to lose their way, rejected by their parent star (e.g. either through a massive gravitational event, and/or because the parent star simply died and withered away).


But new observations of tiny dark clouds called globulettes suggest that free-floaters may be capable or arising within. If true, it would mark only the second known method for planetary formation, the accretion disc theory being the other.


A team of astronomers from Sweden and Finland recently observed globulettes in the Rosette Nebula, a massive cloud of dust and gas about 4,600 light-years away. This nebula is home to about a hundred of these tiny clouds, which feature a diameter no longer than the distance between the Sun and Neptune. Globulettes are incredibly dense — slightly less than 13 times Jupiter’s mass. So these are tiny blotches of dust and gas that are downright planetary.

New measurements show that globulettes, which contain very dense cores, are theoretically capable of collapsing under their own weight. The result: A free-floating planet.


Some of these could take on the characteristics of a brown dwarf — large celestial objects that don’t quite have what it takes to ignite into a sun.

What’s more, owing to the speed of the globulettes within the nebula — estimated at 80,000 km/hr — the rogue planets should be capable of breaking free.


”We think that these small, round clouds have broken off from tall, dusty pillars of gas which were sculpted by the intense radiation from young stars,” explains University of Helsinki astronomer Minja Mäkelä. “They have been accelerated out from the centre of the nebula thanks to pressure from radiation from the hot stars in its centre.”

And because there are literally millions of nebulae in the galaxy, this process could be responsible for millions, if not billions, of rogue planets. Remarkably, astronomers speculate that there may be as many as 200 billion shiftless planets currently coursing through the Milky Way.


Read the entire study at Astronomy & Astrophysics: “Mass and motion of globulettes in the Rosette Nebula.”

Image credit: ESO/M. Mäkelä