Scientists have a hard time figuring out just how common rogue planets, that is planets without stars, are because the primary way to see extra-solar bodies is from the light that their suns reflect off of them.
However now that the planet has been found, the absence of a star actually allows scientists to examine the planet more closely, as it no longer is overwhelmed by the light from a sun.
The discovery came from an international team of scientists with the Canada France Hawaii Telescope and the Very Large Telescope in Chile. The report was also co-authoured by a Canadian, Etienne Artigau, from the University of Montreal.
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“This object was discovered during a scan that covered the equivalent of
1,000 times the [area] of the full moon,” said Artigau told the BBC.
The key way that the team determined that the object is a planet and not a brown dwarf is that they estimate that its temperature is lower than 400C and its size as somewhere between four and seven times that of Jupiter, which, while massive, is far below what would be classified as a star.
Universe Today's Nancy Atkinson notes that the planet's association with a well-defined moving group makes it possible to nail down its characteristics that much more precisely. Plus, it raises interesting prospects: how many of these worlds are there? Potentially lots.
Moving star systems are equally intriguing. The AB Doradus Moving Group is the closest such group to our Solar System, and the stars drift through space together in a pack. They are thought to have formed at the same time. If the new rogue planet actually is associated with this moving group, astronomers say it will be possible to deduce much more about it, including its temperature, mass, and what its atmosphere is made of. There remains a small probability that the association with the moving group is by chance.
The link between the new object and the moving group is the vital clue that allows astronomers to find the age of the newly discovered object. Without knowing its age, it’s not possible to know whether it is really a planet, or a brown dwarf, a “failed” star that lack the bulk to trigger the reactions that make stars shine.
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Free-floating objects like CFBDSIR2149 are thought to form either as normal planets that have been booted out of their home systems, or as lone objects like the smallest stars or brown dwarfs. In either case these objects are intriguing — either as planets without stars, or as the tiniest possible objects in a range spanning from the most massive stars to the smallest brown dwarfs.
“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,” says Philippe Delorme. “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.”