by Peter Jekel
The noise resembles the roar of heavy, distant surf. Standing on the stirring ice one can imagine it is disturbed by the breathing and tossing of a mighty giant below.
Ernest Shackleton
There is a moon out there. Due to an icy exterior, it is one of the brightest objects in the solar system. Several scientists have speculated that it may be the only world in our solar system outside of Earth that is capable of harbouring life which is believed to thrive in a subsurface ocean. That world is named after a Phoenician noblewoman who was courted by the King of the pantheon of Greek gods, Zeus, to become the queen of Crete. She was named Europa. Europa first made its appearance known to humankind on a cold clear January night in 1610, when Galileo Galilei discovered four moons, now known as Galilean moons orbiting the giant planet, Jupiter, one of which was Europa.
There is some controversy that Galileo may not have been the initial discoverer of the moon. In 1614, Simon Marius, a German astronomer published his work entitled Mundus Iovialis, in which he described Jupiter and its moons. In the book, he made the claim that he saw the moons a few days prior to Galileo. The controversy may never be fully resolved. We may have a stalemate and have concurrent independent discoverers; history credits Galileo with the moons' discovery.
The "iceball" moon went by Galileo’s designation of Jupiter II for a long period of time. The names of the moons fell out of favour in the mid-20th century when further astronomical observations discovered more Jovian moons. The use of the Roman numerical designation really was not working anymore so astronomers agreed to go back to the old name of Europa. Marius was now appeased, albeit postmortem, as it was he who named the moon Europa. His names are now used for all the other Galilean moons.
Since the time of Galileo, humans relied on earthbound observations of Europa to promote their theories and ideas. It was only when Pioneers 10 and 11 visited Jupiter in 1973 and 1974 that scientists were offered the first close-up pictures of the moon, albeit limited by the technology of the day the pictures were grainy.
In spite of their poor quality by today’s standards, the photos did allow planetary scientists the opportunity to speculate with some confidence that Europa has a subsurface ocean beneath an ice sheet. When NASA’s Galileo was launched in 1989 and arrived in the Jupiter’s vicinity in 1995, data about Europa increased many times over. Scientists are still sifting through the information. One interesting finding from Galileo is that Europa has an induced magnetic field caused by its interaction with Jupiter. This suggests a subsurface conductive layer, most likely a salty liquid water ocean.
How could a world so far from the sun possibly have a liquid ocean with temperatures reaching as low as -170 degrees Celsius on the surface? Here again, the parent planet, Jupiter, plays a role. Europa’s interior is heated by the tidal flexing by the gravity well of Jupiter, allowing for the presence of liquid water.
There is further evidence that Europa has a subsurface ocean. In spite of the fact that it appears at first sight that Europa is tidally locked, showing the same face to Jupiter at all times, recent observations suggest that the tidal lock may not be full, as a non-synchronous orbit has been proposed. This type of orbit suggests an asymmetry in internal mass distribution which can be explained by a layer of subsurface liquid.
The orbital dynamics appear to indicate a subsurface ocean, and the surface features provide their own evidence. The surface of Europa, made mostly of water ice, is smooth, in fact, it is one of the smoothest objects in the solar system. There are few craters on the surface due to a young changing surface, with some estimates of its age as between 20 to 180 million years, a mere moment in the history of our solar system.
In spite of the apparent smoothness, on closer examination, the surface is actually riddled with dark lines and streaks called lineae which is Latin for “line.” One prevailing theory to explain the lineae is that they are produced as the Europan crust is spread open to expose warmer layers beneath.
Since Europa is almost fully tidally locked to Jupiter, its stress patterns should conform to a predictable pattern. However, only the youngest of the fractures appears to conform to any predictable pattern while older fractures appear to occur at increasingly different orientations the older they are. This is explainable by the fact that Europa’s surface is rotating faster than its interior suggesting that there is a subsurface ocean.
Tidal lock forms the basis of one of the first stories about Europa. It was written by Stanley Weinbaum in 1934 entitled "Redemption Cairn," about an earthlike area of Europa on the Jupiter-facing side of the moon.
There are also other features on Europa that would suggest some interaction between surface ice and a subsurface ocean. The features are called lenticulae which is Latin for “freckles.” An appropriate name, these lenticulae are found to be domes and others are pits both explainable by a subsurface ocean. The domes are suggested to be the result of warm ice rising through the icy crust. The pits are theorized to be caused by melt water breaking through the surface ice.
Now the question is whether or not the ice over the ocean is thick or thin. There is one school that suggests that the outer ice shell of Europa is only a few kilometers thick. If the ice on the surface is that thin, regular contact between the liquid interior with the surface could occur through open ridges. Bud Sparhawk wrote a novella that describes a trek across the icy face of Europa in Ice Dragon's Song. In the novella there are some nice descriptions of the terrain.
There are some geologists, though, that believe that Europa has what is known as thick ice. In this model the ocean would rarely if ever interact with the present surface. The ice in this model ranges from a few kilometers to tens of kilometers thick. Evidence of a thick ice model comes from the study of Europa’s craters--the largest of which are surrounded by concentric rings. Until more data about the surface of Europa is analyzed, the differences of theories will continue.
The surprises of Europa continue as technologies advance. Observations with the Goddard High Resolution Spectrograph of the Hubble Space Telescope in 1995 revealed the unexpected result of an atmosphere on Europa. It has been found to be made up predominately of oxygen but at a pressure though only slightly above that of the vacuum of space. In 1997, Galileo also found evidence of a tenuous ionosphere around the moon created by an interaction of particles from Jupiter with solar radiation further providing evidence of an atmosphere.
Before anybody gets really excited, the oxygen on Europa is not biological in origin. It is created by solar radiation and charged particles from Jupiter interacting with the icy surface and breaking it down into hydrogen and oxygen. Though not biological in origin, observations have shown that some of the oxygen may be making its way to the dark subsurface ocean which would aid potential biology below in the absence of any photosynthetic activity. The hydrogen from the water breakdown can be found in a ring of gas in the vicinity of Europa’s orbit around Jupiter. Both the Galileo and the Cassini, a spacecraft on its way to the Saturn system, “saw” this torus of hydrogen gas.
In March of 2013, NASA published evidence that hydrogen peroxide covers much of the surface of the moon which, if it interacts with the ocean below, would provide another oxygen source: Hydrogen peroxide breaks down into oxygen and hydrogen when it is mixed into liquid water.
With the very strong evidence of a subsurface ocean and an oxygen source in the absence of any photosynthesis, Europa is a prime candidate for alien life to exist. According to some scientists, Europa is even more likely to have native life forms than even Mars. This hypothesis of a life-filled moon is not lost on science fiction writers.
Paul McAuley wrote in his novel The Quiet War about Europa’s subsurface ocean which happens to be the home of the only alien microbial life in the universe. The twist in the novel is that it came from a microbe-laden meteorite from an early solar system collision with Earth billions of years ago.
Up until the 1970’s the idea of life surviving in a subsurface lightless body of water probably would not have been even suggested as a possibility since it was once thought that all life, at least on Earth, was dependent on the energy from the Sun. Sunlight allows plants to photosynthesize producing sugars which, in turn, are eaten by animals. Even, it was thought, life in the deep oceans was dependent on detritus from the surface to nourish life at the ocean bottom.
All of that changed in 1977 when a National Oceanic and Atmospheric Administration (NOAA) deep sea submersible named Alvin did a deep dive at the Galapagos Rift and discovered life made up of entire colonies of giant tube worms, mollusks, crustaceans and other animals which were clustered around undersea volcanoes known as black smokers. These black smokers emit extremely acidic water reaching temperatures of 400 degrees Celsius, harsh conditions for any life form. In addition, there is no sunlight for photosynthesis. Instead, observations found that it was bacteria at the base of the chain, bacteria that do not photosynthesize but derive their energy from the oxidation of chemicals being vented from the black smokers.
Further evidence of potential life lying in a subsurface ocean comes from Antarctica. Russian scientist Peter Kropotkin first proposed the idea of a fresh water body under Antarctic ice sheets at the end of the 19th century. He theorized that the tremendous pressure exerted by the cumulative mass of thousands of vertical meters of ice could increase the temperature at the lowest portions of the ice sheet to the point where the ice would melt. Kropotkin’s theory became fact in 1991 when British scientist Jeff Ridley, using laser telemetry, discovered a subglacial lake, Lake Vostok, named for its location, in Antarctica.
Lake Vostok is just one of up to 400 subglacial lakes now known to exist in Antarctica but it is by far the largest, covering 12,500 square kilometers with an average depth of 432 meters. The lake water is estimated to have been sealed off under the thick ice sheet about 15 to 25 million years ago. It is a nutrient poor environment but compensates by being likely supersaturated with nitrogen and oxygen, up to fifty times greater than surface freshwater lakes on the Earth.
On March 7, 2013, a new bacterium was reportedly discovered in a water sample obtained by Russian scientists Sergey Bulat, a geneticist at the Saint Petersberg Institute of Nuclear Physics. He sequenced the genome and compared it with a global database. Nothing similar was found.
Now if that were not enough to whet your appetite, in November of 2011, researchers reported that in addition to the subglacial ocean on Europa, there may be vast lakes of liquid water encased in the outer shell that are separate from the subsurface oceans. Along these lines, in Kim Stanley Robinson's novel The Memory of Whiteness depicted Europa as the home of human colonies living around pools of melted ice.
Despite the fact that we have earthbound analogues to possible conditions on Europa, the extreme conditions still make it difficult to envision life life as we know it. The water might be too cold or too salty. To be fully confident in our ideas of life on Europa, we must make our way to the alien world to confirm our theories.
There are several planned missions to Europa. One of the planned missions to the Jupiter system is the Jupiter Icy Moon Explorer (JUICE) which was selected by the European Space Agency (ESA) in 2012. The mission is a reworking of an original NASA/ESA cooperative effort that was slated for launch in 2020. NASA had to bow out. The mission will be looking at, in detail, other moons of Jupiter including Callisto, Ganymede and of course, Europa. For the Europan leg of the journey there are plans to do a subsurface sounding of the moon as well as an analysis of the surface components of the moon. The launch, however, is planned for 2022 and will not arrive in the vicinity of Jupiter until 2030.
NASA also has a Europan mission in the works with its Europan Clipper Mission whose aim is to aid in looking for possible future landing sites. It will do this by not orbiting the moon but by low-altitude fly-bys.
Some science fiction authors have looked at the first explorers of the moon. The Curse of Europa by Brian Kayser is about a crew of astronauts who perform the first manned mission to the moon to search for evidence of the liquid ocean and life. Under the ice, they find more than they expected. Allen Steele looked at the possibility of alien life in Europa’s subsurface ocean, framing it as a murder mystery in his novella Angels of Europa.
Others have looked at the first explorers of the moon who not only discover life, but intelligent life. Europa Strike by Ian Douglas is about the finding of an ancient alien spacecraft. In Kim Stanley Robinson’s Galileo’s Dream, colonists of the world live in an underground city carved out of ice; the world beneath the ice is home to enormous sentient organisms. In The Frozen Sky, by Jeff Carlson, explorers find something is alive inside Jupiter's ice moon Europa. When a team of scientists descend through a hieroglyphic lined tunnel into the subsurface ocean they confront a savage race older than mankind.
There are several enormous roadblocks that must be considered if we are ever to colonize Europa. One is the extreme radiation hitting the surface from Jupiter daily, far above a fatal dose for humans. The extreme cold is another hurdle. There is also the possibility that if we venture into the oceans, there may be larger and perhaps aggressive life forms. Not deterred by the hurdles, authors have looked at the possibility of colonizing Europa through terraforming. In Genevieve Valentine's A Bead of Jasper, Four Small Stones terraformers attempt to build a colony on Europa. In a gentler version of terraforming, Arthur C. Clarke’s 2010: Odyssey Two, has advanced aliens taking an interest in the primitive life on Europa and kick-start its evolution. In the sequel novel, 2061: Odyssey Three, Europa, instead of having a cold subsurface ocean, now is tropical world.
Even if the technological hurdles of colonizing Europa appear daunting, there may be other solutions. Science fiction authors have looked at not altering the alien environment of Europa to allow for colonization but to alter the humans living there. Bruce Sterling in Schismatrix envisioned a Europa inhabited by genetically engineered humans. Alastair Reynolds in a short story, "A Spy in Europa," depicts advanced human colonies called Gillies. He also envisioned Denizens as a highly engineered sentient species created on Europa.
Greg Bear looked at the colonization of Europa from an entirely different perspective. Instead of colonizing or terraforming the world, in his story The Forge of God, Europa is destroyed by aliens who use the abundant ice of the moon to terraform other planets.
Other hazards of visiting Europa could be microbial life that is hazardous to human life. Science fiction authors have not shied away from this idea. In "Riding the White Bull" by Caitlin R. Kiernan, probes discover an entire ecosystem in the oceans of Europa. Complications occur when there is an accidental infection of Earth with a sentient microbe.
Finding alien life especially on our cosmic doorstep, even microbial alien life, would dramatically change our views of the universe. It would probably be one of the most life-changing experiences in the history of humankind. The life forms are right there for the observation. We just need the will to go there.
Further Reading
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