Ιώ is one of the many moons of Jupiter, the largest planet in our solar system. It is known for its striking volcanic activity, making it the most geologically active body in the solar system. This activity is primarily due to the gravitational pull from Jupiter and its other moons, which create intense tidal forces. The surface of Ιώ is covered with sulfur and sulfur dioxide, giving it a colorful appearance with shades of yellow, red, and brown. It was discovered by Galileo Galilei in 1610, along with three other large moons, known as the Galilean moons.