Nov 5, 1999

A Volcanic Flashback

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With another Io flyby less than a week away, JPL releases new data showing towering mountains, sizzling hot spots, and enormous lava lakes on Jupiter's fiery moon.




Galileo image of Pele
November 5, 1999: Jupiter's fiery moon Io is providing scientists a look at volcanoes and colossal lava flows similar to those that raged on Earth eons ago, thanks to new pictures and data gathered by NASA's Galileo spacecraft.

The sharp images of Io were taken on Oct. 11 during the closest-ever spacecraft flyby of the moon, when Galileo dipped to just 380 miles (611 kilometers) above Io's surface. The new data reveal that Io, the most volcanic body in the solar system, is even more active than previously suspected, with more than 100 erupting volcanoes.


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Above: Brightly glowing lava from the volcano Pele is seen in this image taken by NASA's Galileo spacecraft as it receded from its close flyby of Jupiter's moon Io in October, 1999. The image at left shows Io's surface in approximately true color, centered on the large red ring of sulfur that was deposited by Pele's plume and reaches more than 1,300 kilometers (808 miles) in diameter. A false color infrared composite of the same region is shown on the right. [more information].

"The latest flyby has shown us gigantic lava flows and lava lakes, and towering, collapsing mountains," said Dr. Alfred McEwen of the University of Arizona, Tucson, a member of the Galileo imaging team. "Io makes Dante's Inferno seem like another day in paradise."

Ancient rocks on Earth and other rocky planets show evidence of immense volcanic eruptions. The last comparable lava eruption on Earth occurred 15 million years ago, and it's been over 2 billion years since lava as hot as that found on Io (reaching 2,700 degrees Fahrenheit) flowed on Earth.

"No people were around to observe and document these past events," said Dr. Torrence Johnson, Galileo project scientist at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA. "Io is the next best thing to traveling back in time to Earth's earlier years. It gives us an opportunity to watch, in action, phenomena long dead in the rest of the solar system."
Parents and Educators: Please visit Thursday's Classroom for lesson plans and activities related to this story.

The new data focus on three of Io's most active volcanoes -- Pele, Loki and Prometheus. The vent region of Pele has an intense high-temperature hot spot that is remarkably steady, unlike lava flows that erupt in pulses, spread out over large areas, and then cool over time. This leads scientists to hypothesize that there must be an extremely active lava lake at Pele that constantly exposes fresh lava. Galileo's camera snapped a close-up picture showing part of the volcano glowing in the dark. Hot lava, at most a few minutes old, forms a thin, curving line more than six miles (10 kilometers) long and up to 150 feet (50 meters) wide. Scientists believe this line is glowing liquid lava exposed as the solidifying crust breaks up along the caldera's walls. This is similar to the behavior of active lava lakes in Hawaii, although Pele's lava lake is a hundred times larger.
Loki, the most powerful volcano in the solar system, consistently puts out more heat than all of Earth's active volcanoes combined. Two of Galileo's instruments -- the photopolarimeter radiometer and near-infrared mapping spectrometer -- have provided detailed temperature maps of Loki. "Unlike the active lava lake at Pele, Loki has an enormous caldera that is repeatedly flooded by lava, over an area larger than the state of Maryland," said Dr. Rosaly Lopes-Gautier of JPL, a member of the spectrometer team.

Left: This collage of images shows the dizzying rate of geologic activity at one of the many erupting volcanoes on Jupiter's moon Io, as viewed by NASA's Galileo spacecraft during the closest-ever Io flyby on October 10, 1999. The top panel shows the best overall view of the Prometheus volcano, combining a picture at a resolution of 120 meters (400 feet) per picture element with a picture at a resolution of 1.5 kilometers (about one mile) per picture element. Inset within this panel is a smaller copy of the mosaic with a temperature map superimposed. [more]

Observations of Prometheus made early in the Galileo mission showed a new lava flow and a plume erupting from a location about 60 miles (100 kilometers) west of the area where the plume was observed in 1979 by NASA's Voyager spacecraft. New Galileo data clarify where lava is erupting, advancing, and producing plumes. The most unexpected result is that the 50-mile (75 kilometer) tall plume erupts from under a lava flow, far from the main volcano. The plume is fed by vaporized sulfur dioxide-rich snow under the lava flow.

Mountains on Io are much taller than Earth's largest mountains, towering up to 52,000 feet (16 kilometers) high. Paradoxically, they do not appear to be volcanoes. Scientists are not sure how the mountains form, but new Galileo images provide a fascinating picture of how they die. Concentric ridges covering the mountains and surrounding plateaus offer evidence that the mountains generate huge landslides as they collapse under the force of gravity. The ridges bear a striking resemblance to the rugged terrain surrounding giant Olympus Mons on Mars.
Visit for coverage of Galileo's close encounters with Io, including science news and the latest images of Jupiter's volcanic moon.
Scientists hope to learn more about dynamic Io when Galileo swoops down for an even closer look on Nov. 25 from an altitude of only 186 miles (300 kilometers). Because Io's orbit is bathed in intense radiation from Jupiter's radiation belts, there is a risk of radiation damage to spacecraft components. In fact, several spacecraft systems sustained damage during the October flyby. Given these radiation risks, the Io flybys were scheduled near the end of the spacecraft's two-year extended mission.

Additional information about the Galileo mission is available on the Galileo home page at a new web address of

JPL manages the Galileo mission for NASA's Office of Space Science, Washington, D.C. JPL is operated for NASA by the California Institute of Technology, Pasadena, CA.

 Web Links

Related Stories:

Sulfuric Acid Discovered on Europa -- September 30, 1999. Sulfur from Io's fiery volcanoes may be responsible for a battery acid chemical on Europa with implications for astrobiology.
Io or Bust -- September 16, 1999. Galileo braves extreme radiation as it plunges toward a close encounter with Io's volcanoes.
Divining Water on Europa -- September 9, 1999. As circumstantial evidence for an underground ocean mounts, JPL scientists try an ingenious experiment to look for hexagonal ice crystals on the surface of Europa.
Taking the Scenic Route to Io -- June 30, 1999. What's happening to the small craters on Callisto? That's the mystery scientists were contemplating as Galileo zoomed past Jupiter's pockmarked moon this morning in an orbit-changing maneuver designed to bring the spacecraft closer to volcanic Io.
Turn Left at Callisto -- May 5, 1999. Galileo heads for a daring encounter with Io's volcanoes.
Galileo buzzes Europa -- Feb. 2, 1999. Galileo executes a close flyby of Europa for the last time during the current mission.
The Frosty Plains of Europa -- Dec. 3, 1998. As Galileo returns new images of Europa, NASA scientists prepare to study samples from a potentially similar environment here on Earth.
Callisto makes a big splash -- Oct. 22, 1998. Scientists may have discovered a salty ocean and a possible ingredient for life on Jupiter's moon.
Galileo takes a close look at icy Europa -- Oct 2, 1998. The spacecraft flew within 2300 miles of the mysterious satellite last weekend.
Clues to possible life on Europa may lie buried in Antarctic ice -- Mar. 5, 1998. Exotic microbial forms turn up in ice above Antarctica's Lake Vostok.

Related Sites:

Ice, Water and Fire the Galileo Europa Mission
Galileo home page at JPL, with the latest on Europa, Callisto and Io
Jet Propulsion Laboratory home page
Io from the SEDS Nine Planets web site
Callisto from the SEDS Nine Planets web site
Jupiter from the SEDS Nine Planets web site
Io: The Prometheus Plume Aug. 18, 1997 Astronomy Picture of the Day
Close-up of an Io volcano Aug. 4, 1995 Astronomy Picture of the Day
Sizzling Io July 6, 1998 Astronomy Picture of the Day


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