NASA officials said what Juno spotted was 'the most powerful volcanic event ever recorded on the most volcanic world in our ...

Earth's Moon: NASA's Galileo spacecraft took this image of Earth's Moon on Dec. 7, 1992, on its way to explore the Jupiter system in 1995-97. The Moon is Earth's only natural satellite.

Because Io is so close to its massive host planet, the moon is subjected to a tremendous gravitational pull as it orbits Jupiter once about every 42 hours, according to the Planetary Society.