Volcanic Explosion on Io
Date: 4 Mar 1979
One of the most surprising discoveries of the Voyager 1 mission was the violent volcanoes of Jupiter's moon Io.
Voyager 1 acquired this image of Io on 4 March 1979 at 5:30 p.m. (PST) about 11 hours before closest approach to the Jupiter moon. The distance to Io was about 490,000 km (304,000 miles). An enormous volcanic eruption can be seen silhouetted against dark space over Io's bright limb. The brightness of the plume has been increased by the computer as it is normally extremely faint, whereas the relative color of the plume (greenish white) has been preserved.
At this time solid material had been thrown up to an altitude of about 100 miles. This requires an ejection velocity from the volcanic vent of about 1,200-miles per hour, material reaching the crest of the fountain in several minutes. The vent area is a complex circular structure consisting of a bright ring about 300 km in diameter and a central region of irregular dark and light patterns. Volcanic explosions similar to this occur on the Earth when magmatic gases expand explosively as material is vented. On Earth, water is the major gas driving the explosion. Because Io is thought to be extremely dry, scientists are searching for other gases to explain the eruption.
What Scientists/Engineers Say About This Image:
"This was really beyond our imagination. It was the first time active volcanoes had been seen on another body in the solar system."
--Dr. Ed Stone: Voyager Project Scientist, Jet Propulsion Laboratory
"The most surprising moon visited by Voyager was Jupiter's moon Io. We had no idea that we could have a moon similar in size to our own moon that had two to three hundred active volcanoes going off on it all the time. We only flew past Io a few times during the Voyager encounters, but every time we did fly by there were hundreds of volcanoes erupting on this moon.
The finding of volcanism on Io really changed our idea of what a habitable zone means in the solar system. We thought that the outer solar system was cold, icy and dead. We also thought that a planet or moon could only have liquid water or sufficient warmth if it was "snuggled up" close to a star. However, we found moons that run on tidal energy rather than sunlight in the outer solar system." More.
--Michelle Thaller: Assistant Director of Science for Communications, NASA Goddard Space Flight Center
Credit: NASA Planetary Photojournal