In the first movie ever made of Jupiter's moon Io in eclipse, volcanic eruptions and auroral emissions glow in the shadow of the giant planet (right). NASA's Cassini spacecraft captured the images that make up the sequence on New Year's Day.
Lava flows from Io's famed volcanoes appear as bright points of light in the new footage. The most brilliant of these, Pele, appears to be erupting steadily, despite its intensity. In contrast, the volcano Pillan, represented by the two spots above and to the right of Pele, has subsided over the past 30 months since its spectacular 1997 eruption. A characteristically different volcano lies below the Pillan hot spots, waxing and waning on a timescale of days.
Atmospheric auroras similar to Earth's aurora borealis and aurora australis account for the ephemeral glow that encircles Io. Brighter glows occur near the moon's equator, creeping clockwise as the eclipse progresses¿the result of the changing orientation of Jupiter's magnetic field. In fact, the new observations provide evidence that these auroras result from electrical currents that flow between Io and Jupiter along magnetic field lines.