We used to think that moons and planets in the outer solar system would be static and unchanging, but upon closer inspection there are a number of very interesting geological and atmospheric processes to study. There are the hydrocarbon lakes on Titan, ice sheets on Europa, and liquid geysers on Saturn’s moon Enceladus. On that last count, things might be changing. A new analysis of activity on Enceladus shows that the activity of the geysers has dropped by 30 to 50 percent compared with their discovery ten years ago.
The geysers on Enceladus were first spotted by NASA’s Cassini probe as it surveyed the Saturnian system. It was a monumental discovery at the time — the first direct evidence of a subsurface liquid ocean outside of Earth. Enceladus was pumping out 250kg of water every second at more than 1300 mph when analyzed in 2005. The volume of water ice being released by this moon is the source of Saturn’s E Ring.
This new measurement of geyser activity on Enceladus is based on photos from the Cassini imaging science subcamera. Scientists are careful to point out that a drop off in activity does not necessarily mean that Enceladus’ geysers are shutting down. We still aren’t entirely clear on how the geysers work, so it’s possible this is part of a recurring cycle. Watching it play out could help scientists understand more about the internal structure of the moon.
Several possible causes for the reduction in activity have been put forward, based on theories of how Enceladus looks inside. As water and ice shoot up through the fissures, there may be a buildup of ice near the surface that slowly closes off the opening and stops as much material from escaping. This could increase pressure until new fissures open or the buildup is dislodged.
The lower activity may also be due to changes at the source inside Enceladus. The water in the moon remains liquid due to tidal forces and heat from Saturn’s gravity, which stretch and compress Enceladus as it orbits. Some previous research from 2013 took images of the geysers and charted the brightness, which should correlate with the volume of water being expelled. That team found that geyser activity seemed to vary based on where Enceladus was in its orbit around Saturn. The flexing might be opening the fissures wider at certain points and compressing them at others.
The new results still have to be peer reviewed and published, but it’s sure to generate a lot of discussion among scientists. Many hope to collect water from these plumes in a future mission, which would offer a handy way to collect a sample from Enceladus without landing. If the geysers will vary or even shut off intermittently, that’s something to know.
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