Spotlight: Lava Flows Freely on Jupiter's Moon Io

Press Release From: Jet Propulsion Laboratory
Posted: Sunday, August 5, 2001

Dr. Rosaly Lopes is on the team for one of the Galileo instruments that has returned information about active volcanoes, the near-infrared mapping spectrometer, or NIMS.

Scientists using NASA's Galileo spacecraft have made many discoveries about the volcanoes on Jupiter's moon Io since Galileo began orbiting Jupiter in 1995. The spacecraft's final three encounters with Io are in August and October, 2001, and January 2002.

Dr. Rosaly Lopes, a volcanologist at the Jet Propulsion Laboratory, is on the science team for one of the Galileo instruments that has returned information about active volcanoes, the near-infrared mapping spectrometer, or NIMS. She is a native of Brazil who earned her doctorate from the University of London. In September 1979, she was doing field research at Mt. Etna, on the Italian island of Sicily, when a crater only about a mile away from her exploded and killed several people. "I really learned to respect volcanoes," Lopes said.

Q: How did you get interested in studying volcanoes on Io?

A: I studied volcanoes on Earth and Mars for my Ph.D. I had just started in 1979, the year Voyager discovered volcanoes on Io, so that was a great excitement. My opportunity to study volcanoes on Io came with Galileo, when I started planning the Io observations for NIMS.

Q: How volcanic is Io?

A: We consider Io the most volcanic body in the solar system because its volcanoes put out the most heat. We have found more than 100 volcanoes on Io, but Earth has more than 600 active volcanoes, so it's not the number that make Io the most volcanic. It's the heat output. Io is only about one-third as big as Earth, but it puts out about twice the energy. One of Io's volcanoes, Loki, is more powerful than all of Earth's volcanoes combined.

Q: Are Io's volcanoes like Earth's volcanoes?

A: Yes and no. The types of eruptions we have observed on Io are similar to types of eruptions on Earth -- lava flows, calderas, fire fountains like in Hawaii -- but there are some very different aspects. One is that lava on Io is much hotter than any lava that flows on Earth today. Billions of years ago Earth had lava that hot. Another difference is that the calderas, the volcanic craters, on Io are much larger than on Earth. Lava flows are much larger, too. [An Io volcano named] Amirani has a lava flow 300 kilometers [190 miles] long, and that's much longer than any on Earth. Globally, Io erupts more than 100 times as much lava per year as Earth, including Earth's undersea eruptions.

Q: Where could you go on Earth that might look like Io?

A: The big island of Hawaii has the Kilauea volcano that has been active for about two decades. Yellowstone is a large caldera that has many areas with brightly colored sulfur. Stromboli [in Italy] has been active for at least 2,000 years. Some very old lava flows on Earth, such as some in South Africa, are a composition called komatiite, which we think is the composition of Io's lavas. Probably the most similar place on Earth just in terms of the great amount of volcanic activity is under the ocean at the mid-ocean ridge.

Q: What makes Io so volcanic?

A: Although both Earth and Io have active volcanism, the way the volcanism happens is quite different. On Earth, volcanism is tied to plate tectonics, and we don't believe Io has plate tectonics. Io is in a tug of war between Jupiter and Europa and Ganymede, two of the other large moons of Jupiter, and that is what heats it up. If Io weren't in its very peculiar orbit around Jupiter, it wouldn't have active volcanism. It would have cooled off a long time ago.

Q: Some people say Io looks like a pizza. What are all those bright colors?

A: We think the bright colors are due to sulfur in various forms but that the very dark colors are due to active lavas. Every place we see high temperatures, if we look at the surface we see dark materials. That would be the olives on the pizza. The reds are deposits from the plumes of volcanoes. With time, the reds become yellow because of changing to a different form of sulfur. We're still quite puzzled by what some of the very small green areas are. We joke and call them golf courses. They may be areas rich in sulfur but contaminated by another material. Another possibility is they are very olivine- rich lava. Olivine is a green mineral.

Q: What is there about Io that is still a mystery to you?

A: We still don't know if Io has its own magnetic field, like the Earth does. That would help us understand the interior. We hope we will still get an answer from Galileo about that. There are other questions that will still remain after Galileo. What is the composition of the lavas? We are using their temperature to say what is the most likely composition based on comparison with lavas on Earth, but we don't really know whether lavas on Io are something entirely different. We won't know that until we can go back with more refined instruments or maybe someday go there and bring back some samples. When we study volcanoes on Earth, one of the first things we do is collect samples of lava and take them back to the lab, but for Io, that's a long way in the future.

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