NASA Solarsystem Collection

Erupting Io

Two tall volcanic plumes and the rings of red material they have deposited onto surrounding surface areas appear in images taken of Jupiter's moon Io by NASA's Galileo and Cassini spacecraft in late December 2000 and early January 2001.

One plume, from the volcano Pele, shoots upward nearly 400 kilometers (250 miles) from the surface near Io's equator. The plume has been active for at least four years and, until now, had been far larger than any other plume seen on Io. The images also show a second plume about the same size, closer to Io's north pole. This plume had never been seen before. It is associated with a fresh eruption from the Tvashtar Catena volcanic area.

The observations were made during joint studies of the Jupiter system while Cassini was passing Jupiter on its way to Saturn. Galileo passed closer to Io for higher-resolution images, and Cassini acquired images at ultraviolet wavelengths, better for detecting active volcanic plumes.

The Cassini ultraviolet images, upper right, reveal two gigantic, actively erupting plumes of gas and dust. Near the equator, just the top of Pele's plume is visible where it projects into sunlight. None of it would be illuminated if it were less than 240 kilometers (150 miles) high. These images indicate a total height for Pele of 390 kilometers (242 miles). The Cassini image at far right shows a bright spot over Pele's vent. Although the Pele hot spot has a high temperature, silicate lava cannot be hot enough to explain a bright spot in the ultraviolet, so the origin of this bright spot is a mystery, but it may indicate that Pele was unusually active when the picture was taken.

Also visible is a plume near Io's north pole. Although 15 active plumes over Io's equatorial regions have been detected in hundreds of images from NASA's Voyager and Galileo spacecraft, this is the first image ever acquired of an active plume over a polar region of Io. The plume projects about 150 kilometers (about 90 miles) over the limb, the edge of the globe. If it were erupting from a point on the limb, it would be only slightly larger than a typical Ionian plume, but the image does not reveal whether the source is actually at the limb or beyond it, out of view.

A distinctive feature in Galileo images since 1997 has been a giant red ring of Pele plume deposits about 1,400 kilometers (870 miles) in diameter. The Pele ring is seen again in one of the new Galileo images, lower left. When the new Galileo images were returned this month, scientists were astonished to see a second giant red ring on Io, centered around Tvashtar Catena at 63 degrees north latitude. (To see a comparison from before the ring was deposited, see images PIA-01604 or PIA-02309.) Tvashtar was the site of an active curtain of high-temperature silicate lava imaged by Galileo in November 1999 and February 2000 (image PIA- 02584). The new ring shows that Tvashtar must be the vent for the north polar plume imaged by Cassini from the other side of Io.

This means the plume is actually about 385 kilometers (239 miles) high, just like Pele. The uncertainty in estimating the height is about 30 kilometers (19 miles), so the plume could be anywhere from 355 to 415 kilometers (221 to 259 miles) high.

If this new plume deposit is just one millimeter (four one- hundredths of an inch) thick, then the eruption produced more ash than the 1980 eruption of Mount St. Helens in Washington.

These Cassini images were acquired on Jan. 2, 2001, except for the frame at the far right, which was acquired a day earlier. The Galileo images were acquired on Dec. 30 and 31, 2000. Cassini was about 10 million kilometers (6 million miles) from Io, 10 times farther than Galileo.

*Image Credit*: NASA

Solar System Exploration

SSE

Space

NASA

National Aeronautics and Space Administration

JPL

Jet Propulsion Laboratory

Planets

Moon

Saturn

Voyager

Galileo

Jupiter

Cassini

Polar

Io

Jet Propulsion Laboratory

Saturn

Jupiter

Washington

Jet Propulsion Laboratory (JPL)

Washington, D.C.

December 2000

January 2001

November 1999

February 2000

2001

1999

2000

SPD-SLRSY-1983

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