Astronomy Picture of the Day

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

August 4, 1995
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Closeup of an Io Volcano
Credit: NASA, Voyager Project, Copyright Calvin J. Hamilton

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 colorful flows up to about 200 miles long emanating from the dark central volcanic vent.

For more information about volcanism on Io, see Calvin J. Hamilton's Io page

Tomorrow's picture: Geysers on Triton

We keep a chronological archive and a subject sorted archive of Astronomy Pictures of the Day.
Astronomy Picture of the Day (TM) is created and copyrighted in 1995 by Robert Nemiroff and Jerry Bonnell who are solely responsible for its content.