Massive sheets of water shooting into space from the surface of Enceladus are exciting astronomers who may be unraveling their ultimate cause. These events, shooting ice and water vapor hundreds of miles above the surface of this moon of Saturn, were once believed to be geysers.

Enceladus, once thought to be a dead, cold satellite, was observed by the Cassini spacecraft in 2005, which saw vast quantities of water shooting into space. Astronomers concluded these events on Saturn's sixth-largest moon were the result of geysers. Now, a new study suggests most of the eruptions observed by scientists are optical illusions caused by sheets of water.

The events appear to be tied to four fractures on the south pole of Enceladus, called tiger stripes. These geological features are named after cities on Earth — Damascus, Baghdad, Cairo and Alexandria. Researchers believe water in the eruptions may originate from a vast ocean lying under the surface of the 310-mile-wide satellite.

Astronomers studied Cassini images of the jets in an effort to better understand the nature of the eruptions. A faint background glow was seen behind the jets in many of the images, suggesting the eruptions were not the result of geysers.

"What became evident very quickly was that a lot of the tiny little jets we looked at were real slippery — we couldn't triangulate them. We also saw really broad areas of emissions that couldn't be jets — they were just huge fuzz," said Joseph Spitale of the Planetary Science Institute.

Simulations were utilized to model the eruptions, and those demonstrations revealed the eruptions were best explained by sheets of water rather than jets. When these outbursts are viewed "sideways," folds in the curtain provide sheets with the appearance of a concentrated geyser burst.

"The viewing direction plays an important role in where the phantom jets appear. If you rotate your perspective around Enceladus' south pole, such jets would seem to appear and disappear," Spitale said.

Jets and geysers could still exist on the surface of Enceladus, although most eruptions are likely the result of the tiger stripe formations, researchers suggest. However, comparisons of Cassini images to the computer simulations show that many of the pictures taken from space were likely the result of walls of water seen at an angle rather than discrete jets.

Curtain eruptions can also be seen rising from fissures on Earth, where molten rock often shoots from deep cracks in the ground.  

Analysis of how jets of water on Enceladus could be explained by a sheet model was detailed in the journal Nature.