Exoplanets, planets which orbit other stars, are now being discovered by the thousands. Current estimates now say that there are likely millions of them in our galaxy alone. But there is another type of planet which had been hypothesized to exist - rogue planets, drifting through space alone, not gravitationally bound to any stars. It's a wild idea, and now the first evidence for just such free-style planets is being found by astronomers.
The best candidate so far was announced yesterday by the European Southern Observatory. The free-floating body, dubbed CFBDSIR2149, is the closest such object found to date, at only about 100 light-years away. It was discovered using the Very Large Telescope and the Canada-France-Hawaii Telescope.
It is thought to be part of a group of nearby young stars called the AB Doradus Moving Group, but is not orbiting any of them.
These kinds of free-floating objects are thought to be "regular" planets which somehow got thrown out of their planetary systems and ended up drifting through space by themselves. They may also form on their own, separate from any stars.
As Philippe Delorme (Institut de planétologie et d’astrophysique de Grenoble and CNRS/Université Joseph Fourier, France) explains, “These objects are important, as they can either help us understand more about how planets may be ejected from planetary systems, or how very light objects can arise from the star formation process. If this little object is a planet that has been ejected from its native system, it conjures up the striking image of orphaned worlds, drifting in the emptiness of space.”
Brown dwarf stars, small stars that failed to "ignite" early on and become full-fledged stars, can sometimes be mistaken for planets. This new candidate is thought to be a gas-giant type planet and not a brown dwarf, but confirming that and learning more about its actual composition will require further study.
If it is indeed part of the AB Doradus Moving Group (an estimated 87% probability), then calculations suggest it would be about 4-7 times the mass of Jupiter, with a temperature of approximately 430˚ Celsius.
Delorme concludes: “Further work should confirm CFBDSIR2149 as a free-floating planet. This object could be used as a benchmark for understanding the physics of any similar exoplanets that are discovered by future special high-contrast imaging systems, including the SPHERE instrument that will be installed on the VLT.”
Some estimates say that these worlds may be common, perhaps even as common as normal stars, an intriguing possibility..