Io (Jupiter I)
1) The fifth of → Jupiter's known moons and
the third largest. It is the innermost of the
→ Galilean satellites.
With a diameter of 3630 km, Io is slightly larger than Earth's Moon. It revolves at
a mean distance of 422,000 km from Jupiter.
Its mass is 8.93 x 1022 kg (about 1.2 Earth Moons) and its
→ orbital period 1.8 Earth days.
The mean → surface temperature
of Io is -155 °C.
Io's yellow color derive from → sulfur
and molten → silicate rock. The unusual
surface of Io is kept very young by its system of active
The intense → tidal force
of Jupiter stretches Io and
damps wobbles caused by Jupiter's other Galilean moons. The resulting
friction greatly heats Io's interior, causing molten rock to explode
through the surface. Io's volcanoes are so active that they are
effectively turning the whole moon inside out. Some of Io's volcanic
lava is so hot it glows in the dark.
In Gk. mythology, Io was a maiden who was seduced by Zeus (Jupiter). When Hera came upon their rendez-vous, Zeus transformed the maiden into a white heifer.