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A moon with atmosphere

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12:55pm, April 12, 2005

Saturn's tiny moon Enceladus has an atmosphere containing water vapor, observations by the Cassini spacecraft reveal. The source of the atmosphere could be icy volcanic eruptions, geysers, or gases escaping from the frigid moon's surface, NASA announced March 16.

Evidence for the atmosphere, which is too tenuous to be imaged, comes from measurements of Saturn's extensive magnetic field taken by Cassini as it flew past the moon on Feb. 17 and March 9. Near the moon, the craft detected oscillations at the exact frequency expected from ionized water molecules gyrating along magnetic field lines. The ions are presumably created when sunlight strikes water vapor emanating from the moon.

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