Astronomy Picture of the Day . ... The closest large moon of Jupiter, Io is the most volcanic moon in the Solar System with its surface being completely buried in volcanic lava every few thousand years. ... Much was learned recently about Neptune's weather by the release last week of time-lapse pictures of the most distant gas giant in our Solar System. ... In this just-released nighttime picture of Jupiter's moon Io, the red spots clearly show Io's current volcanically active regions. ...