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 3, 1995
See Explanation. Clicking on the picture will download the highest resolution version available.
Io: A Volcanic Moon
Credit: NASA, Voyager Project

Explanation: In 1610, Galileo turned his telescope to the heavens and discovered that the planet Jupiter had four bright moons. The innermost of these Galilean moons, Io, turned out to be one of the most exotic objects in the solar system. About the size of the earth's moon, Io is covered with volcanoes, many of which are currently active. The material expelled in the volcanic eruptions may contain compounds of Sulfur which take on a variety of colors and could account for its mottled, "pizza-like" appearance.

For a report of a recent eruption of an Io volcano, see the NASA Infrared Telescope Facility press release and photo .

Tomorrow's picture: Closeup of an Io Volcano.

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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.