Blog 6: Io!

In this blog post, I’d like to talk about the BEST Galilean moon: Io. As I’m sure we all know, Io is known as the volcanic world of Jupiter’s moons. It holds large numbers of volcanoes, and frequent eruptions that repave the surface. In fact, its surface is relatively young with no impact craters. As for any tectonics, Io probably has some tectonic activity, because it usually accompanies volcanism, but debris from eruptions probably buried most of the tectonic features. The volcanoes on Io are also accompanied by outgassing, mainly sulfur dioxide, sulfur, and some sodium. Some of these chemical escape into space where it supplied ionized gas (plasma) to Io Torus and Jupiter’s atmospheres, which gives Io its thin atmosphere. But much of the gas condenses and falls to the surface. This explains that sulfur gives Io its distinctive red and orange colors and sulfur dioxide makes a white frost. Additionally, when the hot lava flows across the surface, it re-vaporizes the sulfur dioxide surface ice in much of the same way that lava flowing into the ocean vaporizes water on earth. Io’s low gravity and thin atmosphere also contributes to allowing the tall plumes of vaporized sulfur dioxide to raise upward to high altitudes. 

Image Source

To explain Io’s internal heat, its size probably contributes a minimal role since it is only the size of a dead moon, so it lost any heat from birth and is too small for radioactivity to provide ongoing heat. Therefore, its source of internal heat must be from tidal heating, which arises from effects of the tidal forces exerted by Jupiter. The tidal force makes Io keep the same face toward Jupiter as it orbits, and Jupiter’s mass makes this force really strong. Io’s orbit is also slightly elliptical because of orbital resonances. Io completes 4 orbits of Jupiter in the same time (7 days) that Europa completes 2 orbits and Ganymede completes 1. The three moons line up periodically, and in each they exert gravitational tugs on each other in same direction, which adds up overtime to stretch out their orbits and make them slightly elliptical.