February 7, 2001

1 min read

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Io in Eclipse

By Kate Wong

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Image: JPL/NASA

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.

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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.

Kate Wong is an award-winning science writer and senior editor for features at Scientific American, where she has focused on evolution, ecology, anthropology, archaeology, paleontology and animal behavior. She is fascinated by human origins, which she has covered for nearly 30 years. Recently she has become obsessed with birds. Her reporting has taken her to caves in France and Croatia that Neandertals once called home to the shores of Kenya’s Lake Turkana in search of the oldest stone tools in the world, as well as to Madagascar on an expedition to unearth ancient mammals and dinosaurs, the icy waters of Antarctica, where humpback whales feast on krill, and a “Big Day” race around the state of Connecticut to find as many bird species as possible in 24 hours. Wong is co-author, with Donald Johanson, of Lucy’s Legacy: The Quest for Human Origins. She holds a bachelor of science degree in biological anthropology and zoology from the University of Michigan. Follow her on Bluesky @katewong.bsky.social

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