Sky lights: picture might show an extrasolar planet.
The near-infrared light comes from an object residing close to a brown dwarf 230 light-years from Earth. A brown dwarf forms as a star, from the collapse of a cloud of gas, but doesn't have quite enough mass to shine as stars do.
In an upcoming Astronomy and Astrophysics, Gael Chauvin of the European Southern Observatory in Santiago, Chile, and her colleagues report that the red object is probably a giant planet, about five times as massive as Jupiter, orbiting the young, 8-million-year-old brown dwarf called 2M1207. The candidate planet would lie 55 times as far from the brown dwarf as Earth does from the sun.
Chauvin's team found the faint body last May with the help of an adaptive-optics system on the European Southern Observatory's Very Large Telescope in Paranal, Chile. The system uses a mirror that continuously changes shape to compensate for the blurring caused by Earth's turbulent atmosphere.
"If confirmed, this discovery will represent a first step toward opening a whole new field in astrophysics: the imaging and spectroscopic study of [extrasolar] planetary systems" says Chauvin. "Such studies will enable astronomers to characterize the physical structure and chemical composition of giant and, eventually, terrestrial-like planets and to search for life out of the solar system."
Although astronomers have discovered more than 125 extrasolar planets since 1995, all of them have been found indirectly, by the wobble they induce in the motion of their parent stars or by the tiny amount of starlight they periodically block. Researchers have made several claims that images of faint objects near bright stars might be planets, but none of the candidates has stood up to scrutiny (SN: 4/22/00, p. 271).
The new find is intriguing because the team recorded a spectrum as well as an image, says planet hunter Ray Jayawardhana of the University of Toronto's Canadian Institute for Theoretical Astrophysics. The spectrum, although containing extraneous signals, suggests that the body contains water vapor and therefore is too cool to be a star or galaxy distant from 2M1207. Using the known distribution of brown dwarfs, the researchers calculate that there's only about a one-in-a-billion chance that the red object is another brown dwarf situated far in front of or behind 2M1207.
The team now plans to track the motion of the red object and determine whether it follows the path of 2M1207 the way it would if it were truly a planet.
Jayawardhana and theorist Adam S. Burrows of the University of Arizona in Tucson suggest that the red object could turn out to be a low-mass brown dwarf that's a companion to 2M1207, rather than a planet. According to a leading theory, planets condense out of disks of ice, dust, and gas that swaddle young stars. Young brown dwarfs may also harbor such disks, but observations indicate those disks are too puny to make planets several times heavier than Jupiter, Jayawardhana says. If Jayawardhana and Burrows are right, the red object would be the lowest-mass brown dwarf ever imaged.
Whether the new object is a giant planet or a low-mass brown dwarf, says Jayawardhana, "I'm excited about the prospect of studying a five-Jupiter-mass object that could shed new light on extra-solar giant planets as well as on broader questions of brown dwarf and star formation."
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|Title Annotation:||This Week; near-infrared light|
|Date:||Sep 18, 2004|
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