Earth Volcanoes Suddenly Not So Scary

Warring with the Gods
According to Greek mythology, the Earth was once a terrible and violent wasteland, inhabited only by warring, monstrous figures. Among them was Enceladus, one of the colossal, serpent-limbed Giants. When the Giants rebelled against the gods, Athena struck Enceladus down with her spear and hurled him beneath Mount Etna, Europe's largest active volcano, for all eternity. So when the ground around Mount Etna rumbled and lava shot into the sky, the Greeks knew the Giant Enceladus was stirring deep underground.

Saturn's Tiny Giant
Some may find it a bit strange, then, that astronomers would one day name a diminutive moon orbiting Saturn after the warring Giant. After all, five of Saturn's moons are larger than Enceladus. And while the Giant Enceladus was a horrifying spectacle, the moon Enceladus is hauntingly beautiful. Covered in an immaculate layer of ice that reflects almost all of the sun's rays, the moon is one of the brightest bodies in the solar system. It also happens to be one of the coldest. According to NASA, the surface hovers around 201 degrees below zero Celsius (330 degrees below zero Fahrenheit). That's more than twice as frigid as the lowest natural temperature ever recorded on Earth. But as a 2005 mission by the Cassini spacecraft confirmed, the moon shares something with its namesake after all: It's the source of some truly spectacular volcanic eruptions.

Of course, the term "volcanic" is a bit misleading. Rather than spewing molten lava like volcanoes on Earth, the cryovolcanoes on Enceladus jettison particles of ice and water vapor with so much force that they fly thousands of miles above the moon's surface. According to astronomers from the University of Virginia, the eruptions are so powerful that they "sandblast" the surface of 11 other moons in the same orbit, polishing them to a reflective shine. In comparison, the scale we use to classify volcanic eruptions on our planet lists an altitude of 15.5 miles as the highest possible magnitude. But Earth hasn't even seen an eruption like that since about 26,500 years ago!

Powerful Forces Beneath the Surface
Even as scientists learn more about the scale and composition of Enceladus' eruptions, however, they are still trying to determine their cause. Originally, astronomers thought the eruptions operated like geysers do on Earth, pulling highly pressurized groundwater from oceans beneath the moon's surface and spraying it up through a series of fissures. The theory was put into question when a study from the University of Colorado at Boulder found that, instead of containing the high levels of sodium one would expect from ocean water, the icy eruptions contained little to no salt at all (though research from the Max Planck Institute for Nuclear Physics found otherwise). Now a variety of hypotheses seek to explain the eruptions.

For instance, some scientists think the eruptions could stem from tidal forces generated by Enceladus' proximity to Saturn. The forces could cause the moon's crust to grind along fault lines referred to as "tiger stripes," creating enough friction to turn the icy surface into liquid water. Another possibility is that the ocean water evaporates from deep underground oceans before slowly working its way to the surface and being pulled into space by the surrounding vacuum, a scenario that explains the lack of sodium in the eruptions. While scientists can't quite agree on the cause of Enceladus' eruptions, they're excited by the prospect of a saltwater ocean lying just beneath Enceladus' surface. After all, Jupiter's moon Europa and Earth itself are currently the only bodies in the solar system known to possess liquid water, one of the basic ingredients for life. If Enceladus is added to that list, the tiny moon may prove to be a giant attraction for future exploration.