Geysers on Saturn Moon Enceladus Hint at Plumbing Mystery
A small water jet on the icy moon spews its fiercest eruptions when the moon is farthest from the planet, but overall gas output hardly increases.
A small water jet on Enceladus, an icy moon of Saturn, spews its fiercest eruptions when the moon is farthest from the planet, a new study suggests, but the overall gas output doesn't increase much during that time. The study points to a mystery in Enceladus' plumbing.
The surprise observation came after looking at the moon using the Saturn-orbiting Cassini spacecraft in March. Enceladus is considered a prime potential location for life because under its icy surface is a global, salty water-ocean that could have the right ingredients for microbes.
Cassini has seen Enceladus erupt many times since arriving in 2004. More than 90 percent of the material in the observed plumes contains water vapor, which researchers said they believe is vented from Enceladus' subsurface ocean. [See Cassini's Amazing Photos of Enceladus]
Previous Cassini observations showed there is three times as much dust sprayed into space when Enceladus is furthest away from Saturn than when it's close by. The new work focused on how much gas erupted along with that dust, propelling it outward. Cassini observed the plume from Enceladus as it blasted in front of Epsilon Orionis, the central star in Orion's belt, and measured the light that passed through that plume using the ultraviolet imaging spectrometer, UVIS. The researchers expected quite a lot more gas expelled at the far part of Enceladus's orbit, to help explain the outpouring of dust, but they found the gas output had bumped up by just 20 percent, far less than expected.
"We went after the most obvious explanation first, but the data told us we needed to look deeper," Cassini UVIS scientist Candy Hansen said in a statement. Hansen, who is based at the Planetary Science Institute in Arizona, led the study's observational planning.
Hansen's team zeroed in on an individual jet nicknamed "Baghdad I." The researchers discovered that this particular jet was four times more active when Enceladus is furthest from Saturn, compared with other times in the moon's orbit.
When Enceladus is furthest from Saturn, Baghdad I's water output alone makes up 8 percent of the observed water plume, which consists of several jets located along "tiger stripes" or cracks in the ice of the moon. At other points in the orbit, Baghdad I's water represents only 2 percent.
"We had thought the amount of water vapor in the overall plume, across the whole south polar area, was being strongly affected by tidal forces from Saturn. Instead, we find that the small-scale jets are what's changing," said Larry Esposito, UVIS team lead at the University of Colorado, in the same statement.
Esposito added, however, that exactly what is happening beneath the surface still puzzles the team. He said he hopes a future set of scientists can model Enceladus' plumbing to come up with some explanations.
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Geysers spout from Enceladus as seen by the Cassini spacecraft. It observed 101 geysers during a campaign in 2010.
On April 3,
. The discovery was made by NASA's Cassini spacecraft that buzzed the 300 mile-wide Saturnian moon on three occasions between 2010 and 2012. This is the first strong evidence of the existence of a sub-surface liquid body of water, but ever since Cassini observed the active moon's water ice plumes, scientists have speculated about their source.
A "snowball" moon: Enceladus is bathed in light in this view from Cassini -- its icy surface exhibits huge cracks, a sure sign of an internal heat source that drives the little moon's famous geysers.
Enceladus' famous plumes are known to be composed of salty water vapor laced with organic compounds, an indication that a sub-surface liquid water reservoir is being heated and blasted through cracks in the moon's icy crust.
A mosaic of the global map of Enceladus, created using images taken during Cassini spacecraft flybys.
In 2012, Cassini captured this view of Enceladus in front of Saturn's rings and bigger moon sibling Titan in the background.
The nightside of Enceladus and backlit plumes of water ice.
A close-up of Enceladus' cracked icy terrain as observed by Cassini. The relative sparsity of impact craters is an indicator of how 'young' the moon's crust is -- ice is continuously cycled with new layers being replaced by tectonic activity.
This 2010 observation by Cassini shows the new and old surface of Enceladus -- a newly created terrain in the upper right meets older, cratered terrain in the lower left.
Small water ice particles fly from fissures in the south polar region of Saturn's moon Enceladus in this image taken during the Aug. 13, 2010, flyby of the moon by NASA's Cassini spacecraft.
This sweeping mosaic of Saturn's moon Enceladus provides broad regional context for the ultra-sharp, close-up views NASA's Cassini spacecraft acquired minutes earlier, during its flyby on Aug. 11, 2008.
A heat map of Enceladus' famous "tiger stripes" -- long fissures etched into the moon's south pole where subsurface water is released as water vapor that quickly freezes to create plumes of water ice particles.
A high-resolution view of Enceladus' vast "tiger stripes" etched into the moon's south pole as observed by the Cassini mission.