November 16, 2012
The astronomy world is abuzz over the discovery of an exoplanet in a nearly unprecedented situation: It’s the first observed to be hurtling through space on its own, rather than orbiting a star. The find, reported by researchers from the University of Montreal in a paper published Wednesday in the journal Astronomy and Astrophysics, is roughly 100 light-years away and has been labelled CFBDSIR2149.
“Although theorists had established the existence of this type of very cold and young planet, one had never been observed until today,” Étienne Artigau, an astrophysicist at the University of Montreal, said in a statement. Over the past decade, astronomers have spotted several candidate objects that could potentially qualify as drifting planets, but the line between what is called a “planet” and what is called a “star” is fuzzy, especially when observing from a distance. Through a telescope, it’s hard to differentiate whether a small solitary object is a “homeless” planet (as the researchers have termed this one) or a brown dwarf, the smallest type of star. The researchers concluded that this is a planet, and one that is 50 to 120 million years old and about 400 degrees Celsius in temperature.
Because this object appears to be traveling through space along with a diffuse group of roughly 30 associated stars called the AB Doradus Moving Group (but does not orbit any of them), the astronomers were able to work out several more pieces of information about it, such as its age, mass and temperature, based on the assumption that the planet likely shares an origin with the rest of the stars in the group. Objects must be less than 13 times the mass of Jupiter to be considered a planet, rather than a brown dwarf, and this object appears to have a mass between four and seven times that of Jupiter, making it an unqualified, starless planet, the first of its kind.
Scientists have speculated that this type of object could result from a normal planet being flung out of its solar system, or could form alone in its present state. Theories of planet and star formation imply that there might be an extremely high number of such solitary planets—they might be as common as normal stars.
For astronomers, the problem is seeing them. Unlike stars, these objects don’t emit a large amount of light. This planet was detected using data from the Canada-France-Hawaii Telescope, located on the summit of Mauna Kea in Hawaii, with further details worked out using the ESO’s Very Large Telescope in northern Chile. Using infrared images from both telescopes, the research team was able to pick out the slight amount of light emanating from the planet, even though it is clearly outshined by the brighter stars:
This image might seem extremely faint, but compared to most exoplanets—which are typically spotted only when they cross in front of the star they orbit or known from how they make their star wobble—astronomers can see this planet much more clearly because there is no competing starlight in the immediate vicinity. “Looking for planets around their stars is akin to studying a firefly sitting one centimeter away from a distant, powerful car headlight,” Philippe Delorme, the lead author of the study, said in a statement. “This nearby free-floating object offered the opportunity to study the firefly in detail without the dazzling lights of the car messing everything up.”
The researchers say that free-floating planets like this one are scientifically significant beyond their apparent uniqueness. “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,” Delorme said. “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.”
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