orbit: 422,000 km from Jupiter diameter: 3630 km mass: 8.93e22
kg The pronunciation "EE oh" is also acceptable. Io was a maiden
who was loved by Zeus (Jupiter) and transformed into a heifer in
a vain attempt to hide her from the jealous Hera. Discovered by
Galileo and Marius in 1610. In contrast to most of the moons in
the outer solar system, Io and Europa may be somewhat similar in
bulk composition to the terrestrial planets, primarily composed
of molten silicate rock. Recent data from Galileo indicates that
Io has a core of iron (perhaps mixed with iron sulfide) with a
radius of at least 900 km. Io's surface is radically different
from any other body in the solar system. It came as a very big
surprise to the Voyager scientists on the first encounter. They
had expected to see impact craters like those on the other
terrestrial bodies and from their number per unit area to
estimate the age of Io's surface. But there are very few, if
any, impact craters on Io. Therefore, the surface is very young.
Instead of cr