A very neat article from CS4K exploring Io, one of Jupiter’s amazing moons!
Way too far away for us to see without special equipment is the moon Io [eye-oh]. It is the 4th largest moon in the solar system traveling around the biggest planet. It is constantly surrounded by a haze of sulfur and other gases, but this is only the beginning of how extraordinary it is.
Io is the only moon in the solar system to have no impact craters on its surface (think of how many our own has). This is because Io is jam-packed with volcanoes. Ever since we developed strong enough instruments to see what was happening, we have observed volcano after volcano erupting, covering the ground with fresh lava.
Because Io is much smaller than earth and has much lower gravity, it can spray material from inside it way up in the sky. Some of these plumes have been seen as high as 400 km (250 miles) above the surface. This tells us the stuff being spewed out is under a lot of pressure, because if you put Old Faithful on Io, it’s spray would only climb to 35 km (22 miles).