May 2, 2007—Jupiter's most turbulent moon, Io, is renowned among scientists for its flashy volcanic displays. But even experts were surprised when they saw this plume of gas vaulting nearly 200 miles (320 kilometers) over the moon's north pole.

The giant frozen jet—about as tall as the state of New Hampshire is long—spewed from a volcano known as Tvashtar in February, just as NASA's New Horizons spacecraft was cruising by on its way to Pluto.

The passing craft captured several images of the event, providing an unprecedented view of volcanism on Io, the most geologically active body in the solar system, scientists said.

"The image of the Tvashtar plume is the best and most detailed plume image that any of us—including longtime Jupiter experts—have ever seen," mission scientist Andy Cheng told the Science@NASA Web site.

The plume likely formed when sulfurous gases released by the volcano crystallized in the frigid vacuum of space, Cheng explained.

Pictures of the massive eruption were part of a suite of recent images from New Horizons that NASA scientists unveiled at a press conference yesterday.

The craft also captured detailed images of a faint ring around Jupiter, close-up shots of the giant planet's Little Red Spot, and a series of mysterious circular troughs on the icy moon Europa.

—Blake de Pastino

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