1) The most volcanically active body in the solar system. With more than 400 active volcanoes, Io doesn't have the cratered surfacecommon to so many other moons: powerful lava flows continually reshapethe landscape. The Ionian volcano Loki, believed to be the solarsystem's most powerful volcano, can spew out up to 1,000 square metersof lava each second.

2) Planetary tides of 100 meters (330 feet). Those are tides pushing and pulling the rocky surface (for comparison's sake,Earth's ocean tides vary by no more than 18 meters or 60 feet). Thetidal forces are exerted in combination by Jupiter and two of its otherlarge moons, Europa and Ganymede. It's the energy generated by these tides, rather than internal heat, that powers Io's geologic activity.

3) Hottest temperatures outside the sun. While the mean surface temperature of Io is quite frosty (-143C or-225.4F), things get hot near active volcanoes. Hot spots discovered bythe Galileo spacecraft showed temperatures of up to 1,610C (2,910F).

4) Tallest mountains in the solar system. Io's active geology builds not only supervolcanoes but super-sizemountains up to 16,764 meters (55,000 feet) tall. That's a far higherclimb than the one up Earth's Mt. Everest, which stands a mere 8,848meters (29,029 feet) tall.

5) Strange ingredients in the atmosphere. Io's very thin atmosphere is mostly sulfur dioxide, but the moon's volcanism helps pump out trace amounts of silicon monoxide, silicon dioxide, iron monoxide and even gaseous salt, potassium and iron."