Scientists Puzzled by Distant Planet-Like Bodies

Oct. 5 -- Scientists are rethinking some basic theoriesabout planets after astronomers found 18 planet-sized gas ballsdrifting free in a star field some 1,200 light years from Earth.

Experts wonder whether faint objects of this size, which havenever before been detected, are failed stars or planets without asun, said Maria Rosa Zapatero Osorio of California Institute ofTechnology in Pasadena, Calif.

“Everybody agrees with our mass determination of these objects,but what we should call them is not decided yet,” said Osorio.“There is a nomenclature problem.”

Osorio is lead author of a study appearing Friday in the journalScience.

Free-Wheeling Planets?

The objects don’t meet the classic definition of a planetbecause they are free-floating and nomadic instead of being lockedinto the orbit of a star, like the Earth and its sister planets inthe solar system.

The smallest of the 18 objects has mass equal to 5 to 8Jupiters, the largest is 13 to 15 Jupiter masses. This puts thelargest on the edge of being a brown dwarf, an object between 15and 75 times the mass of Jupiter.

“We have observed them in the very early stages of evolution,”said Osorio.

Jupiter, the largest planet in the solar system, has a mass 318times greater than the Earth. The sun, which is a star, has a massabout 333,000 times greater than the Earth.

The planet-like bodies are in a star cluster within theconstellation Orion, about 1,200 light years away. A light year isthe distance light travels in a year in a vacuum, about 6 trillionmiles.

Stars That Flopped?

Osorio said the planet-like bodies she found could be “failedstars,” objects that formed independently but never got big enoughto become a star or even a brown dwarf.

Stars are thought to be created when clouds of matter aregravitationally attracted to each other and form a growing ball ofgas. When enough mass is collected, the pressure inside is greatenough to fuse hydrogen atoms and start the nuclear fires that givestars their light and heat.