Io Title We all know that love can move mountains. But is there a force strong enough to move extraterrestrial volcanoes?
Researchers working with data from NASAs Galileo spacecraft have in recent years answered this question with a resounding "yes."
Scientists now say that at least one volcano on Jupiter's small moon Io appears to have "moved" as many as 53 miles (83 kilometers) over the past 20 years. And citing new data collected by Galileo, planetary scientists in this weeks issue of Science have introduced a detailed model for how such an odd phenomenon may work.
"Last November, we realized that we had something truly unique to try to explain," said Dr. Susan Kieffer of Kieffer Science Consulting, the lead author of one of this weeks Science reports. "No volcano on Earth has had its plume pick up and move about 43 miles (70 kilometers) in 16 years. So we started brainstorming."
"We were all really puzzled...Volcanoes on Earth don't move [like that]!"
Io's volcano Prometheus is somewhat similar to Hawaiian volcanoes, though its much larger in overall size. Like terrestrial volcanoes, Prometheus features a huge plume of gas and other particles, reaching miles into the sky. But unlike Earthly volcanoes, Prometheus plume does not emanate from the volcanos caldera, the place from which a main channel of molten lava traditionally flows. Instead, the plume appears to have shifted away from the caldera to a spot about 43 miles to the west -- all in just under 20 years.
"We were all really puzzled by this because volcanoes on Earth dont move [like that]!" said Dr. Rosaly Lopes-Gautier, a researcher at NASAs Jet Propulsion Laboratory (JPL). "The Prometheus movement became a big mystery."
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A plume that moves
Scientists studying Prometheus came to understand early on that the "case of the moving plume" doesnt involve the entire volcano -- its just the plume thats moving.
In 1979, the spacecraft Voyager first flew by Io, capturing images of Prometheus in action. At that time, scientists say, Prometheus gaseous plume was located at or very near the volcanos caldera. But in the resulting 20 years, the plume -- but not the volcano itself -- shifted, apparently following a long lava flow that emanates from the volcanos caldera.
"We believe that this lava flowed out over a frozen ground surface made of sulfur dioxide and/or sulfur," explained Kieffer. Composed mainly of sulfuric compounds, this area of Ios surface is so cold (its a chilly 130 Kelvin, or minus 226 degrees Fahrenheit), that scientists are likening this frozen surface to a "snowfield."
The Prometheus region imaged by Galileo's solid-state imaging camera and by the spacecraft's near-infrared mapping spectrometer in July 1999. Prometheus itself is featured in the center of each image. In image B, hot spots appear red. In image D, dark blue represents high sulfur dioxide frost cover. The area in each panel is about 800 miles (1,285 kilometers) across.
"The lava is hot at its base and melts and vaporizes this snow. This creates a very unstable mixture thatfinds or creates a conduit (pipe) and erupts," said Kieffer. "Thus, the plume is not made of magma in the sense that we think of for most terrestrial volcanoes like Mt. Saint Helens or Pinatubo. It is comprised largely of gas melted by the overriding lava flow."
Though never before observed as extensively, several other volcanoes on Io are thought to show similar pluming behaviors. And in fact, Kieffer holds that there are even similar examples of such volcanic plumes here on Earth, in Iceland and Hawaii, where "lava runs out over marshes or lakes and heats the water, which explodes through the lava."
But nothing so far compares to the 50-mile (80-kilometer) tall plume of Prometheus.
Comparing Io with Earth
One of the benefits of studying such a dynamic planet so far away from Earth, of course, is that it gives scientists a way to compare our home planet and other bodies in the solar system. Scientists agree that although studying Io has provided them with more questions than answers, they are also coming to a better understanding of the different forms planetary bodies can take, depending on how big they are, what theyre made of, and how they interact with their neighbors.
"One of the great advantages of studying other planets is that they teach us about how volcanism and other geologic processes work in other environments," said Lopes-Gautier. "The Prometheus story is really important because it shows a type of mechanism for producing a plume that we have not seen on Earth, except for small scales."
While scientists understanding of Io is still evolving, experts -- with the data collected so far -- have started to theorize about the jovian moons evolution and possible future.
"All of Ios volcanic activity keeps returning us to the fact that the moon has had an extremely hot and dynamic history, and continues to do so," said Kieffer. "[Our] data suggests temperatures approaching 2000 Kelvin (3,140 degrees Fahrenheit), characteristic of lavas called komateites that have not erupted on Earth in the past billions of years. Thus, we are perhaps looking at some aspects of a very early Earth."
The Galileo spacecraft, which is responsible for the huge amount of new data we now have about Io, is scheduled to continue making flybys of Jupiter's moons -- including Io -- until at least the end of 2000. If all goes well, planetary scientists will have a wealth of data to analyze until a future mission picks up where Galileo leaves off.
"There are at present no other missions funded to go back to Io, but we are studying a concept to do this," said Lopes-Gautier. "Io is a very dynamic world and we learn a lot by monitoring its volcanism. Going [there] is not easy, but I hope that there will be another mission soon to follow on the successes of Galileo."
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