You might call them the 13 hippies of the observed universe.
In a recent study of a nearby star-hatchery, two British astronomers have discovered 13 rare "free-floating" objects, which they describe as huge gas planets wandering without an orbit through space.
Patrick Roche of the University of Oxford and Philip Lucas of the University of Hertfordshire confirmed their planet sighting in the autumn of 1999, in what has been touted as the most sensitive survey of the Orion nebula -- a large cloud of gas and dust where stars are continuously forming. Their results will soon be released in an upcoming Royal Astronomical Society publication.
"The objects are likely to be large gas planets similar in size to Jupiter and consisting primarily of hydrogen and helium," said Roche in an e-mail to SPACE.com.
When Roche and Lucas made their discovery, they were looking for faint stars and brown dwarfs -- gaseous objects that cannot accumulate enough material to activate the type of nuclear reaction that a star needs to keep glowing. But they soon noticed a number of objects that were even dimmer than brown dwarfs.
"From the measured brightness and the known distance to the Orion nebula, we knew they did not have enough material for any nuclear processing in their interiors," explained Roche.
After scrutinizing various theoretical models of planetary objects the same size they were seeing, Roche and Lucas say theyre fairly certain that the objects truly are planets.
"The combination of luminosity and age (known to be between 0.3 and 2 million years old) gives us a fairly good measure of the mass," added Lucas. "Hence, were pretty sure theyre planets."
Free spirits
Whats most interesting about the 13 new planets is that they apparently do not orbit a star in the same way that the planets in the solar system orbit the sun. Instead, they appear to wander aimlessly through space.
"We would see a [central] star if they orbited one," explained Lucas.
Only two other similar objects had been found before Lucas and Roches 13-planet discovery. Two years ago, Japanese astronomers detected two non-orbiting planet-like objects in the Chamaeleon nebula.
Dr. Roche said that the 13 objects "probably formed in a different way from the planets in our solar system" in that they were not made "out of the residue of material left over from the birth of the sun." Instead, they formed "like stars via the collapse of a cloud of cold gas," explained Lucas.
"But they possess most of the physical properties and structure of gas giant planets," added Lucas.
Scientists hope the discovery of such wandering objects will give them clues to the relationship between small stars and large gas planets. With continually increasing telescope capabilities, the prospects of finding similar gas planets and hopefully even terrestrial planets is on the rise.
"This is a very active research field," said Roche. "Undoubtedly more objects will follow."
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