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Brown dwarfs called 'missing link' between planets, stars

LOS ANGELES -- Too massive to be planets and too cold to be stars, five stellar wannabes are finally earning some cosmic respect.

The recently discovered gaseous objects fall into a new category below stars and above planets, said Davy Kirkpatrick, staff scientist at the Infrared Processing and Analysis Center at NASA's Jet Propulsion Laboratory in Pasadena."They're kind of a hybrid between planets and stars -- sort of a missing link in the astronomical world," he said.

The news was announced Tuesday by astronomers who are surveying the sky with telescopes that detect heat emitted from stars and galaxies hidden from view by interstellar dust.

Typical brown dwarfs, so named because of their relative size and darkness, do not have enough mass to start the nuclear fusion engine that powers stars like the sun. Even though they're called cool, they still generate some heat from collapsing gases.

Still, even among brown dwarfs, the five new objects are unusually cool. Scientists detected the presence of methane, a gas that only forms at less than 1,652 degrees Fahrenheit -- just four times the temperature of a typical kitchen oven.

"The ones we're seeing are really the coolest objects of the bunch," Kirkpatrick said. "Because (the methane dwarfs) are so cool, they're able to form molecules in their own atmosphere, unlike stars."

The Jupiter-size objects also are not associated with nearby stars and appear to be "lost in space," he said.

The methane brown dwarfs, estimated to be about 30 light years from Earth, are located in the constellations Leo, Virgo and Corvus and the Big Dipper area of Ursa Major. They cannot be seen with a naked eye.

"Because our telescopes can only see the closest examples, this means the Milky Way must be brimming with objects like these," Kirkpatrick said.

The brown dwarfs were discovered while researchers analyzed data gathered by telescopes in Arizona and Chile as part of the Two-Micron All Sky Survey, a project sponsored by NASA and the National Science Foundation.