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.

July 19, 1996

Galileo's First Colour Image of Io
Credit: Galileo Project, JPL, NASA

Explanation: Above is the first colour image of Jupiter's volcanic moon Io released by the Galileo Project. (Io sounds like "eye-oh".) The image was made on June 25 when the Galileo spacecraft approached within 1.4 million miles. It reveals features as small as 14 miles across - comparable to the resolution of the best 1979 vintage Voyager images. The Voyager flybys discovered active volcanos on Io's mottled surface and this image indicates that dramatic changes have occurred since, notably in the region of the Masubi volcano located in Io's southern hemisphere. This region, apparently covered with new deposits of sulfur and sulfur dioxide frost deposited by volcanic eruption, is seen as the pronounced white area at the bottom of the picture. While scientists continue to analyze this image and other recent Galileo data the robot spacecraft will continue to explore Jupiter's moons. Its next scheduled close encounter is set for September 6th with the moon Ganymede. Higher resolution images of Io are also expected during the ongoing mission.

Tomorrow's picture: Vikings on Mars

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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.