Magazine article Science News

Io's Big Sodium Cloud Looms Even Bigger

Magazine article Science News

Io's Big Sodium Cloud Looms Even Bigger

Article excerpt

Io's big sodium cloud looms even bigger

The large, crescent-shaped cloud of sodium atoms that stretches out into space from Jupiter's moon Io, fed by Io's volcanic eruptions, has intrigued astronomers since its discovery in 1973 from Earth. Studies of the fog-lamp-colored cloud have indicated that traces of it extend out into space from Io as far as 30 times Jupiter's radius, or about 2.1 million kilometers.

Now a group of researchers has observed the could again, finding evidence of its sodium atoms more than 32 million km out from Jupiter.

It is "possibly the largest permanently visible feature in the solar system," says astronomer Michael Mendillo of Boston University.

New observations by Mendillo and two co-workers, made with a ground-based telescope, reveal the cloud has an angular width of about six degrees, a portion of the sky, as viewed from Earth, equivalent to that of a dozen full moons placed side by side.

The sodium atoms are carried away from Io by processes associated with Jupiter's rapidly rotating magnetosphere, or magnetic field. The researchers, in fact, don't call the feature a could at all, but a "magneto-nebula."

Mendillo, together with Boston University colleague Jeffrey L. Baumgardner and graduate student Brian C. Flynn, reported their results last week at the American Geophysical Union meeting in Baltimore.

The group photographed the cloud on Jan. 25 from McDonald Observatory in Fort Davis, Texas, using a 100-millimeter telescope. …

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