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.

October 27, 1996

Io's Active Volcanoes
Credit: Galileo Mission, JPL, NASA

Explanation: Why is Io green at night? In this just-released nighttime picture of Jupiter's moon Io, the red spots clearly show Io's current volcanically active regions. But what is causing the global green sheen? This telling picture was taken by the automated Galileo spacecraft currently orbiting Jupiter while Io was in Jupiter's shadow. One hypothesis is that the green glow is caused by a different type of aurora resulting from high-energy particles interacting with Io's volcanic plumes.

Tomorrow's picture: The Weather on Neptune

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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.