APOD: September 20, 1999 - Io in True Color (original) (raw)

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.

September 20, 1999

Explanation: The strangest moon in the Solar System is bright yellow. This recently released picture, showing Io's true colors, was taken in July by the Galileo spacecraft currently orbiting Jupiter. Io's colors derive from sulfurand molten silicate rock. The unusual surface of Iois kept very young by its system of active volcanoes. The intense tidal gravity of Jupiter stretches Io and damps wobbles caused by Jupiter's other Galilean moons. The resulting friction greatly heats Io's interior, causing molten rock to explode through the surface. Io's volcanoesare so active that they are effectively turning the whole moon inside out. Some of Io's volcanic lava is so hot it glows in the dark.