Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

August 4, 1995

Closeup of an Io Volcano
Credit: NASA, Voyager Project

Explanation: In 1979, one of NASA's Voyager spacecraft made a spectacular and unexpected discovery. Io, the innermost Galilean moon of Jupiter, was covered with volcanoes and some of them were erupting! In all, Voyager 1 observed nine volcanic eruptions during its encounter with the moon. When Voyager 2 flew past four months later it was able to confirm that at least six of them were still erupting. This Voyager image of Ra Patera, a large shield volcano, shows colourful flows up to about 200 miles long emanating from the dark central volcanic vent.

For more information about volcanism on Io, see `Views of the Solar System' Io page

Tomorrow's picture: Geysers on Triton

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
A service of: LHEA at NASA/ GSFC
&: Michigan Tech. U.