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Warnings: The True Story of How Science Tamed the Weather by Mike Smith tells the story of our storm warning system. See our online store book collection.
This is a drawing of the interior of Io.

What Io is Made of

The air of Io is roughly 90% Sulfur, and 10% other simple atoms such as Oxygen.

An idea of the interior composition can be guessed from the density of Io, which is about 3.5. The density of iron is about 5, and that of silicate rock is 3, so the inside of Io must be made out of rocky material and sulfur.

Deep inside Io is probably a core made of heavier metal elements such as iron. This is where the magnetosphere of Io may come from.

The composition of Io is very different from the other icy satellites and suggests a certain path for Io's evolution.

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