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Change Your Life! |
Nomadic Planets! |
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October 6, 2000
WASHINGTON (AP) - Eighteen planet-sized gas balls, wandering free and unattached to any star, have been found in a star field some 1,200 light years from Earth. Astronomer Maria Rosa Zapatero Osorio of the California Institute of Technology said it is the largest collection of isolated, free-floating planet-like objects ever found and astronomers are at a loss just what to call them. "There is a problem of nomenclature," said Zapatero, the first author of a study appearing in the journal Science. She said the objects are not like traditional planets, which are bound by gravity to a central star such as the sun. And they are too small to be brown dwarfs, an object much smaller than a star, but bigger than a planet. For now, she is calling them "planetary mass objects." Other astronomy teams have found a total of about 50 planets outside the solar system, but all of those planets were in orbit of central stars. "The formation of young, free-floating planetary-mass objects like these are difficult to explain by our current models of how planets form," said Osorio. Planets in the solar system, such as the Earth, are thought to have evolved from debris left after the formation of the sun. Planets formed in this way would be gravitationally locked into an orbit of the central star. Joan R. Najita, an astronomer at the National Optical Astronomy Observatory in Tucson, Ariz., said that Osorio's discovery is significant and may force astronomers to reconsider theories about planets. There is, said Najita, "an incomplete understanding of how these objects could have formed." The nomadic planets range in size from 5 to 8 times bigger than Jupiter, the largest of the solar system planets, to about 13 times bigger than Jupiter. Generally, objects 13 times the mass of Jupiter are classified as planets, while bodies between 13 and 75 times bigger than Jupiter are considered brown dwarfs. Osorio said that the size of the objects is based on their brightness and on an analysis of the light - the spectrographic characteristics - that suggests a planet-like temperature and composition. The objects are in a star cluster field called Sigma Orionis within the constellation Orion.
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