Io is one of the four large moons that orbit Jupiter. Similar in size to our moon, Io is also the most volcanically active body in our solar system.
Io has massive volcanoes that launch sulfur over 200 miles into the sky. Every minute, 60 tons of sulfur escape from the surface of Io and form a glowing trail behind the moon. This trail shows up in pictures as a ring-shaped cloud around Jupiter.
If this moon didn't have volcanoes or sulfuric lakes, humans might be able to go here—with oxygen tanks, that is. There is no oxygen or water on Io. Therefore, the choking atmosphere would poison and kill an oxygen-tank-less human in an instant.
When the first Voyager space probe went past Io in 1979, scientists couldn't believe their eyes. Instead of seeing a frozen, dull surface like they had predicted, they saw a volcanically active fireball. Four months later, Voyager II passed Io and scientists noticed a few changes on the moon including increased volcanic activity, more lava flows, lava lakes, and sulfur.
Scientists predict that Io's volcanic activity may burn out many years from now because the orbital process that heats the planet has slowed down. Gravitational interactions with other moons of Jupiter continue to heat Io, but the volcanic eruptions cool the moon faster than it can heat up.
In the future, it’s probably safest for all Earthings to keep an eye on Io from a distance!
[Source: Secrets of the Universe]