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article imageLost in Space: Orphaned planet may help explain planet formation

By Robert Myles     Nov 14, 2012 in Science
Using the European Southern Observatory (ESO) Very Large Telescope and the Canada-France-Hawaii Telescope, astronomers have discovered an orphaned planet meandering through space without a parent star or solar system.
Free floating planets are not a new discovery. Scientists have known of their existence since the 1990s but what makes the new find so exciting is the relative proximity of the floating planet to Earth and the absence of any bright star close to it. This has allowed scientists to examine its atmosphere in great detail says the European Southern Observatory in a newly published report.
Up till now, it has been difficult to determine whether an ‘orphan’ planet was actually a brown dwarf star. A brown dwarf is a type of ‘failed’ star whose mass is insufficient to trigger the fusion reactions that cause stars to shine. More recent studies have pointed to there being huge numbers of these floating planets in our Milky Way galaxy, possibly as many as twice the number of main sequence stars.
The newly discovered object, designated CFBDSIR2149, appears to be part of a nearby stream of newly formed stars called the AB Doradus Moving Group. It was first detected by the Canada-France-Hawaii Telescope, after which astronomers used the powerful ESO Very Large Telescope to examine it more closely.
The AB Doradus Moving Group is the closest such stream of stars to our Solar System. It has the characteristic of being a group of stars, thought to have been formed at the same time, drifting through space together. If it is confirmed that CFBDSIR2149 is part of the same moving group then it becomes possible to deduce a lot more about it such as its temperature, mass and atmospheric composition. Should CFBDSIR2149 be confirmed as associated with the AB Doradus Moving Group this would indicate the mass of the planet to be approximately 4 to 7 times the mass of Jupiter, with an effective temperature of approximately 430 degrees Celsius. The planet’s age would be the same as the moving group itself, between 50 and 120 million years.
CFBDSIR2149 is the first planet sized candidate astronomers have so far found likely to be part of a moving group and this is why the discovery is generating such interest.
Astronomers believe free-floating objects like CFBDSIR2149 form either as normal planets ejected from their original solar systems or as solitary objects in space. Says Philippe Delorme of the French Institut de planétologie et d’astrophysique de Grenoble (Grenoble Institute of Planetology and Astrophysics), lead author of the new study, “Looking for planets around their stars is akin to studying a firefly sitting one centimetre away from a distant, powerful car headlight. This nearby free-floating object offered the opportunity to study the firefly in detail without the dazzling lights of the car messing everything up. 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.”
According to the European Southern Observatory, if it transpires that CFBDSIR2149 is not associated with the AB Doradus Moving Group it becomes more difficult to be certain of its nature and properties. It is possible it could be characterised as a small brown dwarf. Either way, its existence poses important questions about how planets and stars come to be formed and behave.
“Further work should confirm CFBDSIR2149 as a free-floating planet,” concludes Philippe Delorme. “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.”
Further information can be found in the ESO research paper enititled “CFBDSIR2149-0403: a 4-7 Jupiter-mass free-floating planet in the young moving group AB Doradus?” published today.
More about Solar system, Star formation, origin of stars, Astronomy, Astrophysics
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