Weird things can happen in the strange, cold, and dimly lit domain of the four giant gaseous planets of our Sun's enchanting family. Of the Quartet of majestic outer planets – Jupiter, Saturn, Uranus, and Neptune – the gas-giant Saturn stands out in the crowd because of its great beauty, gossamer rings, and myriad of dancing, sparkling icy moons and moonlets. Enceladus (en-SELL-ah-dus), a frozen moon of Saturn, is one of the brightest objects in our Solar System because it is covered by a shell of dazzling water ice that reflects sunlight like recently fallen, sparkling snow. In May 2015, planetary scientists published new research indicating that most of the famous eruptions bursting out from Enceladus's tiger stripes might actually be diffuse curtains rather than the discrete jets that they were previously thought to be – strange, icy phantoms created by an optical illusion .
Indeed, the features on this dazzling little moon-world – that appear to be individual jets of material erupting along the entire length of its intriguing tiger stripes –may not be what they seem to be. The playfully named tiger stripes are prominent fractures streaking across and scarring Enceladus's south polar region, and they got their name because they resembled the stripes on the coat of a tiger.
"We think most of the observed activity representations curtain eruptions from the tiger stripe fractures, rather than intermittent geysers along them. , "noted Dr. Joseph Spitale in a May 6, 2015 NASA Jet Propulsion Laboratory (JPL) Press Release. Dr. Spitale is the lead author of the study, published in the May 7, 2015 issue of the journal Nature under the title Curtain eruptions from Enceladus' south polar terrain. He is a participating scientist on the Cassini mission at the Planetary Science Institute in Tucson, Arizona. The JPL is in Pasadena, California.
NASA's Cassini spacecraft began its long and productive study of the Saturn system on July 1, 2004, when it zipped into orbit around the intense, distant world – and started to snap some very revealing images. Cassini will continue its exploration of the planet, its many moons, and its majestic rings until September 2017, when it will be significantly crashed head long down into Saturn's thick, gaseous atmosphere.
Enceladus has the highest albedo of any moon in our Solar System as a result of its sparkling white surface coating of highly reflective ice. Indeed, Enceladus reflects almost 100 percent of the sunlight that strikes it, and because it reflects so much sunlight, its surface temperature is extremely frigid, at about -330 degrees Fahrenheit. The little moon-world also has an extremely active geology, which has caused it to be almost completely free of craters. This is because Enceladus is constantly being resurfaced by the erupting ice shooting out from its tiger stripes , which are also the source of bright, fresh snow that keeps the surface of the little moon both smooth and dazzling.
Only about as wide as the state of Arizona, Enceladus displays at least five different types of terrain. Portions of the strange moon show craters no larger than about 22 miles in diameter, while other areas show no craters at all – indicating major resurfacing events in the geologically recent past. There are also plains, corrugated terrain, fissures, and other crustal scars. All of this suggests that the interior of this dazzling little moon-world may be liquid, even though it should have turned to ice long ago. The bewitching surface of Enceladus is thought to be geologically youthful – perhaps less than 100 million years old.
A Sparkling Little Moon In The Saturn System
Planetary scientists considered the possibility of an interior reservoir of life-sustaining liquid water benefit the surface ice of Enceladus back in 2005, when Cassini spotted water vapor and ice flying out from the tiger stripes near its south pole. Indeed, recent observations indicate that liquid water – even even a subsurface global ocean – swirls around beneath Enceladus's shell of bright ice. Where liquid water exists, life as we know it has the potential to evolve. The discovery of a large interior ocean hidden beneath Enceladus's surface ice hoists it up into the highest tier of potentially life-sustaining bodies in our own Solar System – along with Europa of Jupiter, another icy moon that also harbors a hidden subsurface global liquid water ocean. Both of these small, ice-covered moons demand much closer scrutiny.
Saturn is the smaller of the gas-giant duo dwelling in the outer regions of our Solar System – Jupiter is by far the largest. Uranus and Neptune, the two other planet denizens of the outer Solar System, are classified as ice giants. This is because they have more massive cores and thinner gaseous envelopes than the two gas giant planets. With its famous and beautiful system of magnificent rings, Saturn has captivated observers for centuries. Until 2004, no spacecraft had visited Saturn for about a generation. Pioneer II had taken the very first long trip to the ringed-planet in 1979, when it sped past it, snapping the first close-up images of this intense, gaseous world. Voyager 1 had its own close encounter a year later, and in August 1981 Voyager 2 made its own brief, but productive, visit. Finally, in 2004 Cassini entered the domain of this intriguing gas-giant planet, and started to cast some revealing light on its many mysteries.
The icy eruptions on Enceladus are likely the result of its close proximity to its parent-planet, according to information provided by the Cassini spacecraft. The icy jets shooting out from the surface of the moon have been compared to adjustable garden hose nozzles. The nozzles are most open when Enceladus is farhest away from its planet, and almost entirely closed when it is closer to it. Planetary scientists think that this is caused by the way Saturn hugs and then releases the little moon-world that is caught in the grip of its gravity.
Cassini spotted jets shooting out from a very bright plume in 2005. The water ice is mixed with organic particles and shower out from the tiger stripes . The warm vents that are responsible for creating the tiger stripes shoot out huge masses of ice, water vapor, and organic particles – launching this frozen brew hundreds of miles into interplanetary space. This is a little gift of sorts for planetary scientists, because it provides them with a way to observe the subsurface ocean from a great distance.
Phantoms Create An Optical Illusion On Enceladus!
In the process of analyzing Cassini's images of Enceladus, Dr. Spitale and his team paid particular attention to the fault background glow existing in most of the images. The brightest eruptions, which appear to be discrete jets, seems to be superimposed intermittently upon this haunting, fault background glow.
The planetary scientists modeled eruptions on Enceladus as uniform curtains along the tiger stripe fissures. They discovered that phantom brightness improvements appear in places where the viewer is looking through a "fold" in the distant curtain. The folds exist because the fissures, tear through the icy surface of this moon-world, are more wavy than perfectly straight. The researchers believe that this is really an optical illusion responsible for most of what seem to be individual jets.
"The viewing direction plays an important role in where the phantom jets appear. Spitale explained to the press on May 6, 2015.
In the supercomputer simulated images produced by the scientists, phantom jets line up nicely with some of the features observed in real Cassini images that seem to be discrete columns of spray. The correspondence between simulation and spacecraft data indicates that much of the discrete jet structure is really an illusion, according to the researchers.
Curtain eruptions occur on our own planet where molten rock, or magma, rushes out of a deep fraction. These eruptions, which often create spectacular curtains of fire, are seen in places such as the Galapagos Islands, Hawaii, and Iceland.
"Our understanding of Enceladus continues to evolve, and we've come to expect surprises along the way." commented Dr. Linda Spilker in the May 6, 2015 Press Release. Dr. Spilker is Cassini project scientist at the JPL.