July 15, 2001
Every candle on your cake is a tiny imitation of the stars that made you possible.
Io in True Color
Birthday · July 15, 2001
A little universe, just for you
Your date.
Ready to give.
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APOD published July 15, 2001. Full image credits are on the original APOD entry below. A publication-date match, not a photo taken on your date. Independent of NASA.
The strangest moon in the Solar System is bright yellow. This picture, showing Io's true colors, was taken in 1999 July by the Galileo spacecraft currently orbiting Jupiter. Io's colors derive from sulfur and molten silicate rock. The unusual surface of Io is 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 volcanoes are 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.