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.

December 31, 1996
See Explanation.  Clicking on the picture will download 
 the highest resolution version available.

Io Rotating
Credit: The Galileo Project, JPL, NASA

Explanation: Are any volcanoes on Io currently erupting? To help answer this, scientists instructed the robot spacecraft Galileo to take hourly pictures of this moon of Jupiter prior to its most recent encounter. The most obvious changes in Io are due to the changing amount of sunlight reflected from the moon to the spacecraft. More careful inspection does verify continuous volcanic plumes. The most prominent plume visible is from Prometheus, visible just below Io's equator. This plume was first photographed in 1979 by Voyager, so Prometheus appears to have been erupting continuously for at least 18 years! On most browsers, the above picture will appear animated. To stop the movie, click on your broswer's "stop" button.

Tomorrow's picture: Aurora Over Circle, Alaska

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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.