Io

Io is the innermost and smallest of the Galilean moons.

Economy

Io is heavily geared towards industrial production, housing such powerhouses of industrial production such as the Io Munitions Works, the Io Toxic Disposal Plant, and military facilities such as the Io Weapons Testing Facility, and the Io Training Camp.

Orbital parameters

Mean orbital distance: 421,600 km
Rotational period: 1.769138 days
Orbital period: 1.769138 days
Mean orbital velocity: 17.34 km/sec
Orbital eccentricity: 0.004
Orbital inclination: 0.040 degrees

Io orbits at an average distance of 421 700 km from Jupiter. It is locked in a Laplace-resonant orbit with Europa and Ganymede in such a way that for each orbit Ganymede completes around Jupiter, Europa will complete two. While Europa has completed those two orbits, Io will have completed four orbits. This process, where the moons interact gravitationally, along with strong gravitational forces exerted by Jupiter is probably the cause of Io's volcanic surface.

Io's "body" is bent and stretched about 100m in this process, which causes it to heat up. The surface is never completely solid (about 2000 K hot), but it is continuously resurfaced. Io is the most volcanic active body in the Sol system, with lava flows, lava lakes, and giant calderas covering its landscape. Its mountains reach heights of 16 kilometers. On its current orbit, it will never have a completely solid surface, but always be scarred with volcanoes and liquid sulphur.

Volcanoes have spew out gas and dust at heights of 400 km. But Io's orbit happens to lay where Jupiter's magnetic field is particularly strong. When material is ejected from the volcanoes it is to an extent carried on by Jupiter's magnetic field which also accelerates it to an amazing speed of 300km/s. As the Jovian magnetosphere rotates, it sweeps past Io and strips away about 1,000 kilograms per second of volcanic gases and other materials. This produces a neutral cloud of atoms orbiting with Io as well as a huge, doughnut shaped torus of ions that glow in the ultraviolet. The torus's heavy ions migrate outward, and their pressure inflates the Jovian magnetosphere to more than twice its expected size. Some of the more energetic sulfur and oxygen ions fall along the magnetic field into Jupiter's atmosphere, resulting in spectacular aurorae. The matter that isn't picked up by the magnetic field crystallizes to sulphurous flakes and falls back as snow.

Planetary parameters

Mass: 8.94e+22 kg
Equatorial radius: 1,815 km
Mean density: 3.55 gm/cm^3
Escape velocity: 2.56 km/sec
Visual geometric albedo: 0.61
Mean surface temperature: -143°C

Studies show that Io has a magnetic field of its own, along with an atmosphere consisting of sulphur compounds. The moon acts as an electrical generator as it moves through Jupiter's magnetic field, developing 400,000 volts across its diameter and generating an electric current of 3 million amperes that flows along the magnetic field to the planet's ionosphere.

Based on density, surface composition analysis, and gravity data, Io appears to be a rocky silicate rich body that has a dense iron, iron sulfide core that extends halfway to the surface with a partially melted silicate rich mantle, and a thin rocky crust. The lower density of Ganymede and Callisto suggest that they are composed of lighter elements, most likely water in some form. Why are there such differences among the four Jovian satellites? During the early formation of the solar system, Jupiter would have been very hot. This may have prevented lighter elements from condensing at the inner orbits. The mini system of Jovian satellites orbiting Jupiter is like a miniature version of the rest of the solar system, with the rocky, dense planets at the innermost orbits and the light, least dense planets at the outer orbits.