Jupiter’s Moon Io

Jupiter’s moon Io is one of the four Jovian moons collectively referred to as the Galilean satellites. Europa, Callisto, and Ganymede are the others. Io is 3,642 km in diameter. It is the fourth largest moon in the Solar System as well as being the most volcanically active body in our Solar System.

Io features at least 400 active volcanoes. On Earth, volcanoes are created when tectonic plates shift in such a way the subsurface magma is able to flow onto the surface(Yes, that is an oversimplification, but adequate for these purposes). The volcanoes on Io are created by gravitational tides from Jupiter. The tidal forces from the planet actually force Io’s surface to bulge up and down by as much as 100 m, causing magma to flow continuously. By comparison, the tides on Earth’s oceans, even in the place where tides are highest, the difference between low and high tides is only 18 m.

This continual tidal push and pull generates a tremendous amount of heat within Io, keeping much of its subsurface crust in liquid form. Without the tidal forces, Io would have cooled millions of years ago. The volcanic eruptions keep the surface of Io constantly renewed. Lava fills in any impact craters with molten lakes or spreads out as smooth new floodplains of liquid rock. Some scientists theorize that the lava is mostly molten sulfur and its compounds, which would account for the varied colors of the moon. Other theories suggest that it could be made of silicate rock pointing out that the seeming high temperatures are too hot for sulfur. Sulfur dioxide is the main component of Io’s atmosphere. Data from the Galileo spacecraft indicates that an iron core may form Io’s center, thus giving Io its own magnetic field.

The constant volcanic activity on Io, in turn, contributes to Jupiter’s magnetic field. The planet strips material from Io at a rate of one ton per second. This material becomes ionized, then diffuses into the rest of the region surrounding Jupiter, becoming a major source of the charged particles trapped in the Jovian magnetic field. Jupiter’s rapid rotation, intense magnetic field, and this abundant source of particles create a huge reservoir of electrons and ions. These charged particles, trapped in Jupiter’s magnetic field, are continually accelerated into the atmosphere above the polar regions. There they collide with gases and produce auroras that far exceed anything seen on Earth. These auroras rarely ever end.

The New Horizons spacecraft sent back a great deal of data about Io before moving on to the edges of the Solar System. The exact material that makes up Jupiter’s moon Io may be discovered when the Juno spacecraft arrives in orbit around Jupiter. We will have to wait until July of 2016 to find out.

We have written many stories about Io here on Universe Today, including this one about Galileo’s last visit to Io, and how hot Io can get.

Here’s NASA’s Solar System Explorer information on Io, and this great picture from Astronomy Picture of the Day of Io hovering over the surface of Jupiter.

We’ve also recorded an entire show just on Jupiter for Astronomy Cast. Listen to it here, Episode 56: Jupiter, and Episode 57: Jupiter’s Moons.

Source:
NASA