Europa, an icy little moon that circles the giant planet Jupiter, probably sustains a global ocean of liquid water beneath a tortured, shattered icy crust. For a long time, weird and jumbled regions of ice disruption, called “chaos terrains”, were seen only on Europa, and their origins remained cloaked in mystery. But astronomers now think that the “chaos terrains” formed as the result of a subsurface liquid saltwater lake, equal to all of the Great Lakes on Earth combined. Hidden about 1.9 miles beneath Europa’s cracked eggshell-like frozen crust, the ice-embedded lake may be one of the latest potentially habitable environments discovered so far in our Solar System.
Europa, is a fascinating, frigid little world. It is one of the four Galilean moons, discovered in January 1610 by the great Galileo Galilei when he was gazing up into the night sky with his small, primitive “spyglass”. The other Galilean moons, the weird sisters of Europa, are Io, Ganymede, and Callisto.
Europa is the sixth largest moon in our Solar System, and few bodies have enticed astronomers as much as this little moon of Jupiter, because it is thought to sport a subsurface global ocean of liquid water–and where there is water, there is the possibility of life. The more astronomers learn about this fascinating and mysterious icy moon, the more they become enchanted with it.
Although Europa was visited by the two spacecraft Pioneer 10 and Pioneer 11 in the early 1970s, and the twin Voyagers in 1979, these early flybys only produced grainy, dim images. However, these early pictures revealed enough about the little moon to make it intriguing. Pale yellow icy plains were seen in the Voyager images. The plains also tantalizingly displayed red and brown mottled areas. Long cracks were observed, running for thousands of miles over the shattered eggshell-like crust. On Earth, similar cracks would suggest such features as high mountains and deep canyons. But nothing higher than a few kilometers was seen on the moon. In fact, Europa is one of the smoothest bodies in our Solar System.
NASA’s Galileo spacecraft imaged Europa during a flyby on September 7, 1996. In fact, so far there have only been flyby missions to this fascinating object. Galileo viewed Europa’s surface much more closely than the Pioneers and Voyagers, and it revealed to astronomers a bizarre surface that looked like broken glass, repaired by an icy glue oozing up from below.
The most detailed pictures of Europa show even more intriguing clues that there is slush lurking beneath its brightly shining icy surface. Slightly smaller than Earth’s own beloved Moon, Europa’s surface temperature could easily freeze an ocean solid over a span of only several million years. However, some astronomers think that warmth from a game of tidal tug-of-war between Europa and Jupiter, as well as other neighboring moons, could be keeping large regions of Europa’s subsurface global ocean in a life-friendly liquid state. This process is termed tidal heating, and it refers to a mechanism whereby the gravitational tugs of a nearby object (or objects) flex and bend and contract and expand another object continually. This constant churning causes the victimized object, in this case Europa, to heat up and be considerably more balmy than its great distance from the Sun would otherwise allow it to be.
Images of Europa taken by Galileo in 1997 provide some important evidence suggesting that Europa may be slushy just beneath its glistening cracked icy crust–and possibly even warmer at greater depths. This evidence includes an oddly shallow impact crater, chunky-looking textured blocks of surface material that tantalizingly resemble icebergs on Earth, and openings in the surface where new icy crust appears to have formed between continent-sized plates of ice.
Some of the images focus on the shallow center of a bizarre impact crater dubbed Pwyll. Impact rays and shattered pieces of material scattered over an immense area of the moon tell the tale of a sizeable meteorite that collided violently with Europa relatively recently–“only” about 10 to 100 million years ago. There is also darker debris chaotically scattered around Pwyll. This further suggests that the large crashing meteorite may have dug up some deeply buried material, and tossed it helter-skelter around the crater.
However, the crater’s shallow basin and tall surrounding mountain peaks may be whispering the precious secret that the subsurface ice was warm enough to collapse and fill the deep hole created by the impact.
The “chaos terrains” are those regions of the icy moon that are covered with shattered, scrambled, and rotated chunks of crust the size several city blocks. Galileo images show swirly and very rough-looking material between the broken blocks of ice, which indicates that the blocks may once have been lodged atop a bed of slushy stuff that ultimately froze at the very frigid surface temperatures of Europa.
“For decades scientists have thought Jupiter’s moon Europa was a likely place for life, but now we have specific, exciting regions on the icy moon to focus our future studies, ” Dr. Don Blankenship, senior research scientist at the University of Texas at Austin’s Institute for Geophysics, commented in the November 16, 2011 National Geographic News.
In a study released in November 2011, Dr. Blankenship and his colleagues discovered the enormous subsurface lake on Europa by carefully scrutinizing two bumpy, circular features in the old Galileo images, taken about a decade earlier. The “chaos terrains” were shown to be bizarre regions of floating and colliding icebergs and ice flows. This jumbled mess collapsed portions of the little moon’s ice shelf.
The team further ascertained the presence of the enormous, embedded lake by drawing a connection between processes seen on Europa and processes seen on our own planet. Ice-piercing radar, that can delve through thick layers of ice sheets, has been used to locate numerous subglacial lakes in Antarctica.
An orbiting spacecraft sporting such an ice-piercing radar is necessary to confirm and map Europa’s enormous lake. NASA is considering such a mission, proposed to launch sometime before 2022.
There probably are many more lakes under Europa’s ice, Blankenship continued to note. Furthermore, the prospects of searching for life on Europa could greatly improve. This is because research indicates that a percentage of the icy lids that cover the embedded lakes may be considerably thinner than was previously supposed.