At least some of the narrow jets that erupt from the surface of Enceladus do so with increased fury when the moon is farther from Saturn.

Previous Cassini observations showed that the volume of ice particles jetting out of Enceladus triples when the moon is farthest from Saturn. But scientists had never had a chance to observe a change in the amount of gas (water vapor), which comprises 90 percent of the material in the plume.

In March, Cassini’s ultraviolet imaging spectrometer (UVIS) stared at Epsilon Orionis, the central star in Orion’s belt, as the plume of Enceladus passed between the star and the instrument, and gas in the plume dimmed the star’s ultraviolet light. Scientists expected to find that the gas vented far more intensely in this part of the moon’s orbit similar to the way the volume of ice particles had tripled. Instead, they found the gas increased by only 20 percent.

The researchers then looked nearer to Enceladus’ surface at an individual jet and found it was releasing four times more gas than usual. It may be that the volume of gas from some jets doesn’t increase much, but that the observed three-fold increase in ice particles is driven by a handful of jets releasing more gas that lofts the particles. More ›