NASA/JPL/University of Arizona

In this movie, the inner-most satellite of Jupiter, Io, is in the eclipse shadow of Jupiter (Jupiter is blocking the Sun for Io). This allowed NASA's spacecraft Cassini to image the active moon in darkness. These images were taken over a two-hour period and nearly capture the entire eclipse which took place on January 1, 2001. The spacecraft was over 10 million kilometers (6.3 million miles) away, yielding a resolution of 61 kilometers (40 miles) per pixel on these images.

Glows on Io

While Io is enshrouded in darkness, several glows are revealed to us. The bright points of light are hot lava from the active volcanoes on Io. The brightest of these is the volcano Pele which appears to be erupting constantly. To the right and slightly above Pele is a pair of bright spots from the volcano Pillan, the source of a major eruption in 1997. A second source of glow on Io is the faint, diffuse emission of atmospheric aurorae. Similar to the aurora borealis (northern lights) on Earth, the aurorae on Io result from collisions of charged particles (from the electrical currents that flow between Jupiter and Io) with gases in Io's tenuous atmosphere. The aurorae are seen here as a faint glow around Io's equator.

Ellen Cohen