The Geysers of Enceladus May be an Illusion
The erupting geysers on Saturn's Enceladus may not be geysers at all, they might just seem to appear when viewed from certain angles.
Saturn's moon Enceladus has a subsurface ocean that vents the liquid water through long cracks in its icy crust, but as planetary scientists get more familiar with the geysers blasting from the moon, new subtleties are presenting themselves.
Through the analysis of observational data from NASA's Cassini Saturn-orbiting spacecraft and computer modeling, scientists are beginning to realize that when it comes to Enceladus' geysers that erupt from the moon's polar "tiger stripes", there's more than meets the eye.
"We think most of the observed activity represents curtain eruptions from the ‘tiger stripe' fractures, rather than intermittent geysers along them," said Joseph Spitale, a participating scientist with the Cassini mission at the Planetary Science Institute in Tucson, Ariz. "Some prominent jets likely are what they appear to be, but most of the activity seen in the images can be explained without discrete jets."
In short, in new research published today (May 7) in the journal Nature, Spitale's team think that Enceladus' discrete geysers are an illusion.
Called "curtain eruptions", the researchers believe that vapor is being ejected along Enceladus' tiger stripes, which are often wavy fissures. As the vapor is ejected along these wavy features, depending on the angle you're viewing the eruptions from, you will sometimes be looking through the bend or ‘fold' in the curtain of vapor. These folds will make the scattered light from the vapor appear more intense, giving the illusion of being a discreet geyser.
"The viewing direction plays an important role in where the phantom jets appear," said Spitale. "If you rotated your perspective around Enceladus' south pole, such jets would seem to appear and disappear."
Curtain eruptions occur on Earth in regions of volcanic activity - such as Hawaii, Iceland and the Galapagos Islands. Molten rock can erupt from long fissures, often creating impressive curtains of fire.
"Our understanding of Enceladus continues to evolve, and we've come to expect surprises along the way," said Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory, Pasadena, California, who was not involved in the study. "This little ice world is becoming more exciting, not less, as we tease out new details about its subsurface ocean and astonishing geophysical activity."
Phantom jets in simulated images produced by the scientists line up nicely with some of the features in real Cassini images that appear to be discrete columns of spray. The correspondence between simulation and spacecraft data suggests that much of the discrete-jet structure is an illusion.
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.