In what could be a breakthrough in the search for worlds, an international team of astronomers claims to have made an image of a planetlike object beyond our solar system. If confirmed, this would be astronomers' first direct peek at an extra-solar planet.
Previous discoveries have relied on indirect evidence, such as eclipses or the "wobbles" of stars. Now, researchers may have a real picture.
The team, led by Gael Chauvin of the European Southern Observatory in Chile, still has to determine if the object travels as a pair with a nearby "failed" star, known as a brown dwarf. Indicators suggest that the object is about five times as massive as Jupiter, orbiting a "failed star" some 230 light years away.
Some astronomers suggest that this lightweight companion could itself be a brown dwarf. Either way, the find is remarkable, according to Ray Jayawardhana, a professor of astronomy and astrophysics at the University of Toronto. "It really doesn't matter what you call it. It will really open up to us the physics of low-mass objects" that form the sometimes blurry boundary between oversized planets and undersized stars.
"We're finding yet again an amazing diversity of objects out there that defy our simple - and, in many cases, antiquated - labels," Dr. Jayawardhana says.
Typically, astronomers have searched for planet-size objects around other stars by using two indirect methods. One method uses wobbles in a star's light-borne chemical fingerprint - shifts in its spectral lines - to determine if it has a planetary companion. The other looks for the planet to cross in front of the star, slightly dimming its light.
But nothing beats seeing one directly.
For Dr. Chauvin and his researchers, the effort pushed their telescope and detectors to the limit.
With new detection gear hooked to the European Southern Observatory's Very Large Telescope in Chile's Atacama Desert, the group systematically examined hundreds of stars identified as young and close - only tens of millions of years old and a couple of hundred light-years away. The reasoning: If these stars were close enough and young enough, any planets orbiting them might still be giving off heat - perhaps enough to be detected in the infrared, says team member Ben Zuckerman, an astronomer at the University of California at Los Angeles.
When the researchers trained their telescope on a brown dwarf that was part of a larger collection of young stars, it appeared to have a dim companion 55 astronomical units away - 55 times the distance between the earth and the sun. The companion's spectrum included water vapor, which ruled out any possibility that it was a more distant, dust-reddened galaxy.
Brown dwarfs - star wannabes that failed to accumulate enough mass to ignite their nuclear furnaces - tend to exist as companions to more mainstream stars. But lone brown dwarfs are so rare that the chance of having two in the same field of view was close to one in a million, Dr. Zuckerman explains.
The team took the companion's temperature and - based on theories about the relation of a brown dwarf's temperature and mass - calculated that it tipped the cosmic scales at five times Jupiter's mass.
Other teams have reported possible sightings of extra-solar planets, only to have them turn out to be more mundane objects.
"This is the first apparent success we've had" in searching for them directly, says Zuckerman, whose results have been accepted for publication in the journal Astronomy & Astrophysics. "And it's a more plausible candidate than others."
Jayawardhana agrees. But he also holds out the possibility that the object could be a rare binary brown dwarf. The interpretation hinges on which approach to large-planet formation one favors.
The conventional explanation: These planets first form with rocky cores built out of the disk of dust and gas that forms around a young star. Once formed, the cores attract the lighter gas surrounding them in a case of runaway growth.
But this process takes about 10 million years, Zuckerman says, while their planet candidate formed 8 million years ago. Zuckerman suggests an alternative: that massive outer planets can form much like stars do. Within the nebula of dust and gas around a budding star, other "clumps" can separate, contract, and draw in nearby material, becoming planets.
Jayawardhana holds that this second approach also is how a binary companion can form around a brown dwarf.
Either way, the find is "wonderful," he says. "Remember the first brown dwarf was identified barely a decade ago. Now astronomers have found a planetary mass companion to a brown dwarf, and we're wondering what to call it."