NASA’s Cassini probe, which is orbiting Saturn, has provided some of the most beautiful imagery we’ve seen transmitted from beyond the confines of our terrestrial home. (And its images sometimes include our terrestrial home.) Sure, Saturn itself is great and all, but the gas giant’s rings and moons are simply fantastic. There’s Titan, with its thick, hazy atmosphere and methane cycle—complete with rivers, lakes, and precipitation. And then there’s Enceladus—the smooth, icy wonder that might harbor a liquid water ocean beneath its surface.

Enceladus is best known for the geysers near its south pole, which shoot water vapor and microscopic particles of water ice high above the surface. Some falls back to Enceladus and the rest escapes, forming one of Saturn’s rings. The geysers have attracted attention for good reason. Simple organic compounds like methane, propane, and formaldehyde have been detected in the plumes of water, as has ammonia. That gets people excited about what kind of chemistry could be going on beneath the surface—and whether it might even include biochemistry. And then there’s the most basic question: why is the interior of Enceladus so warm, anyway?

The prevailing explanation is that it’s caused by gravitational variations, which go about squeezing and stretching Enceladus. This is caused by its slightly elliptical orbit around Saturn—sometimes closer to the gas giant, sometimes farther. The shape changes happen pretty rapidly, as Enceladus completes a lap around Saturn in just under 33 hours.

These potent tidal effects were predicted to have an observable influence on the activity of the geysers by alternately pulling apart and squeezing together the fissures they escape through, but at the time, we hadn’t had enough data to test that idea. Cassini has now been orbiting Saturn since 2004, making for a lot more up-close-and-personal time with Enceladus. A group of researchers have used infrared observations of Enceladus’ geysers to examine the way they change as the icy moon zips around Saturn.

Measurements of the infrared brightness of the geyser plume aren’t quite as simple as they sound because Cassini’s view of Enceladus varies. Simply changing the orientation of Cassini and Enceladus can make the plume look brighter or darker. But given enough measurements (the researchers used 252 images for the analysis), those details can be accounted for, creating a consistent measure of how much water Enceladus’ geysers are geysering throughout its orbit.

As it turns out, the plume was over three times brighter in infrared (meaning more water was coming out) when Enceladus was farthest from Saturn compared to when it was closest. The geysers are clearly modulated by the gravitational interaction with Saturn. There are also hints in the data that the plume reaches higher above Enceladus at the farthest point in its orbit, meaning that it’s blasting out at a greater velocity.

In a related article for Nature, John Spencer of the Southwest Research Institute in Colorado describes how this could help us learn more about what’s going on beneath the surface of Enceladus. The model used to successfully predict how its fissures would respond to tidal forces, he says, “treats Enceladus’ crust as a thin elastic shell that is detached from the interior by a fluid layer, such as a global ocean. Global-ocean models have fallen out of favor for Enceladus, because it is difficult to keep a global ocean from freezing, and a regional south polar ocean is now considered more likely. Such refined models can now be tested and constrained by their ability to match the observed plume behavior.”

Nature, 2013. DOI: 10.1038/nature12371 (About DOIs).