On January 7, 1610, the Italian astronomer Galileo Galilei peered at Jupiter through a primitive telescope he had fashioned.  He described what he saw as “three fixed stars, totally invisible by their smallness,“ but over the next few nights, he noticed one more point of light, and that they changed positions.  Moreover, they moved in a direction that was opposite that of the other stars.  He eventually concluded that these were not truly “stars” but were actually four moons of Jupiter and they were subsequently called Io, Ganymede, Callisto and Europa.  But of the ninety-five Jovian moons that we know now, Europa is the most promising on which to discover life. In fact of the 290 objects in our solar system that most people would consider to be a moon, Europa has the best chance of harboring life as we understand life. This blog will explore the mysteries of Europa in the search for life.

Vital stats

Europa is tidally locked as it revolves around Jupiter.  Tidal locking occurs when the same side of a moon faces the planet as all times, as with our own moon.  Until probes were launched during the last half century which were able to orbit our moon and return photographs, no one had ever seen the “dark side” of our moon.  Tidal locking occurs when the period of rotation on the moon’s axis equals its period of revolution.  With our moon, it’s pretty equal.  With Europa it is close, but not perfect.

Not only moons can be locked in this way, but planets, as well (such as Mercury) as it orbits the Sun.  With Mercury, the daylight side reaches temperatures of 800 degrees Fahrenheit.  On the dark side of Mercury, temperatures can drop to minus 290 degrees Fahrenheit.  But between these two extremes wouldn’t there be a place where the temperature is between plus 60 and plus 100 degrees Fahrenheit?  It might be a narrow corridor, perhaps only a few feet wide.  Could there be life there?  Lichen? Primitive plants?

There is no weather or wind on Europa, because there is hardly any atmosphere on that moon.  There reason for this is because there is barely and gravity to hold an atmosphere.  In fact, the gravitational attraction of Europa is only thirteen percent that of Earth.  Our moon, by contrast, has seventeen percent of earth’s gravity.

Europa is almost twice the distance from Jupiter as our moon is from Earth.

The surface of Europa

Europa is a bit smaller that the Earth’s moon.  Unlike most moons in the solar system (including our own), Europa has been spared the pockmarks of meteor collisions throughout the ages.  The smooth surface of Europa suggests that there is some sort of liquid or ice on the surface.  And there is other evidence to support this hypothesis as well.

The Hubble Space Telescope and the Galileo space craft revealed plumes of geyser-like water erupting from the surface of Europa.  Geologists on earth belief that these geysers may be throwing up evidence of life to the surface of the moon.  These geologists say:

Surface temperature on Europa are thought to be -210 degree F in the darker areas and -370 degrees F in the lighter areas.  This extreme weather leads to unusual ice formations, including what are called penitentes because they resemble the white pointed hats worn by monks in Spain who sought repentance.  The conditions on Europa as we know them now might produce penitentes that are fifty feet high!  Penitentes occur on Earth, but are not nearly as large.

Chaos terrain

Not all of Europa is frozen ice.  There are regions where the surface rock is exposed.  Rock on earth plays an important role in the beginning of life.  An article in Carnegie Institution’s Elements magazine sums it up.

“The contributions of rocks and minerals to life’s geochemical origins were not always so well appreciated. The pioneering experiments of University of Chicago graduate student Stanley Miller and his mentor, Harold Urey, revealed that organic molecules essential to biology form abundantly when a simple mixture of reduced gases is subjected to electrical sparks. . . Within a decade, a growing army of origins chemists followed their lead to synthesize most of life’s essential molecules— amino acids, lipids, sugars, and more.”

And speaking of rock, in another post I discuss the prospects of silicon-based life, though that might be a long shot for Europa.

“Europa’s surface contains a lot of what’s called Chaos Terrain. That’s where surface features like plains, ridges, and cracks are all jumbled together, appearing chaotic. The features were moved and jumbled around before they froze in place. Other bodies like Pluto, Mars, and Mercury also have Chaos Terrain.

“There’s a lot of scientific debate about Europa’s surface, and what causes the Chaos Terrain. Impact events where the impactor penetrates the ice surface into a liquid crust is one possibility. Or it might be because of the heating and stretching that Jupiter’s gravity forces on Europa, and how the sub-surface oceans respond to that. Scientists think that Europa’s lineae are caused by eruptions of warm water, and that lineae are sort of like cracks between tectonic plates.

“Crisscrossing Bands areas are made up of both ridges and cracks. A ridge is likely the result of repeated opening and closing of cracks. It’s kind of like how mountains form on Earth, when two plates push against each other.

“A crack is a smoother area, created when an area pulls apart horizontally. These are wide, flat areas, where water might flow into the opening and re-freeze, forming newer smooth surfaces.”

What lies beneath

Based on close observations of the planet from the Hubble Space Telescope, the Galileo probe which arrived in the Jovian neighborhood in December 1995, spectrographic analysis, radio signals and so on, Europa is thought to have water.  A lot of water.  Salty water.

Wikipedia notes that: 

“Research suggests . . . the tidal locking may not be full, as a non-synchronous rotation has been proposed: Europa spins faster than it orbits, or at least did so in the past. This suggests an asymmetry in internal mass distribution and that a layer of subsurface liquid separates the icy crust from the rocky interior.”

Wikipedia goes on to note:

“It is estimated that Europa has an outer layer of water around 100 km (62 mi) thick – a part frozen as its crust and a part as a liquid ocean underneath the ice. Recent magnetic-field data from the Galileo orbiter showed that Europa has an induced magnetic field through interaction with Jupiter’s, which suggests the presence of a subsurface conductive layer. This layer is likely to be a salty liquid-water ocean.”  NASA agrees: “Based on Europa’s icy composition, scientists think the most likely material to create this magnetic signature is a global ocean of salty water.” 

“Europa’s ocean lies below a shell of ice probably 10 to 15 miles (15 to 25 kilometers) thick, and has an estimated depth of 40 to 100 miles (60 to 150 kilometers.)” 

Even if only 60 miles deep, it would be nine times as deep as the deepest part of earth’s oceans.  In the Pacific Ocean, somewhere between Guam and the Philippines, lies the Marianas Trench, also known as the Mariana Trench. At 35,814 feet below sea level, its bottom is called the Challenger Deep — the deepest point known on Earth.

The Prospects for life on Europa

“Europa is considered one of the most promising currently habitable environments in our solar system.  Europa could have all the “ingredients” needed for life as we know it:

• Water: Evidence suggests there is a global ocean over twice the volume of Earth’s oceans combined. 
• Organics: Scientists believe it’s likely that the essential chemical building blocks for life exist on Europa, stemming from the moon’s formation and from asteroid and comet impacts. 
• Energy: Scientists believe Europa may have the chemical energy sources needed for life. This includes surface radiation from Jupiter and potential interactions between water and a rocky seafloor. 
• Stability: Europa’s ocean may have existed for the entirety of our solar system’s history, approximately 4 billion years.” 

On Europa, sunlight is much less than here on Earth.  “This deep into the solar system, Europa’s underground ocean wouldn’t feel the warmth of the sun; it would stay liquid because of Jupiter’s gravitational tugging,” according to an interesting article in The Atlantic magazine. And even on Earth, the wreck of the Titanic at 12,500 feet lies in darkness.  That depth is nothing in an ocean that could be as deep as 100 miles.  So, then, how could life survive at those depths?  One answer might be through hydrothermal vents like we have near the deepest—and coldest—ocean floors on Earth.

Hydrothermal vents

“Organisms on Earth have been discovered in the subglacial lakes of Antarctica and in the hot ion-rich waters of hydrothermal vents. Life in Europa’s subsurface oceans could be supported in similar ways.”

NOAA has done a lot of pioneering work with these vents.  

“Scientists first discovered hydrothermal vents in 1977 while exploring an oceanic spreading ridge near the Galapagos Islands. To their amazement, the scientists also found that the hydrothermal vents were surrounded by large numbers of organisms that had never been seen before. These biological communities depend upon chemical processes that result from the interaction of seawater and hot magma associated with underwater volcanoes.

“Hydrothermal vents are the result of seawater percolating down through fissures in the ocean crust in the vicinity of spreading centers or subduction zones (places on Earth where two tectonic plates move away or towards one another). The cold seawater is heated by hot magma and reemerges to form the vents. Seawater in hydrothermal vents may reach temperatures of over 700° Fahrenheit. 

“Hot seawater in hydrothermal vents does not boil because of the extreme pressure at the depths where the vents are formed.”  Yet, it’s possible that a certain residual amount of heat might percolate the many miles above to the surface, according to Alyssa Rhoden, a planetary geophysicist at the Southwest Research Institute who studies Europa:

“’When you look at Europa’s surface, you can see a lot of pits where the surface seems to have dropped down a little bit, places where the surface has been disrupted,’” Rhoden [states.] “’We think that that’s happening from heating coming from below.’” (ibid. The Atlantic.)

And, of course, assuming the oceans are in fact forty, sixty, or one hundred miles deep doesn’t mean that there aren’t any “shelves” or shallow, submerged plateaus just below the surface which may be more conducive for life.

So, the “organisms” mentioned above in many cases form “communities” around the vents (see photo of a vent absent any notable or visible lifeforms.)  The vents provide heat for the aquatic life, of course, but also “chemical” nutrition.

“’Black smokers’ are chimneys formed from deposits of iron sulfide, which is black. ‘White smokers’ are chimneys formed from deposits of barium, calcium, and silicon, which are white.”

What life forms can we expect?

The type of life that might inhabit Europa likely would be powered purely by chemical reactions instead of by photosynthesis, because any life at Europa would exist beneath the ice, where there is no sunlight.  That might be where the hydrothermal vents come in.

“Europa’s surface is blasted by radiation from Jupiter. That’s a bad thing for life on the surface – it couldn’t survive. But the radiation may create fuel for life in an ocean below the surface. The radiation splits apart water molecules (H2O, made of oxygen and hydrogen) in Europa’s extremely tenuous atmosphere. If we eventually find some form of life at Europa it may look like microbes, or maybe something more complex. If it can be demonstrated that life formed independently in two places around the same star, it would then be reasonable to suggest that life springs up in the universe fairly easily once the necessary ingredients are present, and that life might be found throughout our galaxy and the universe” according to NASA.

There is something interesting about the radiation that reaches the surface of Europa.  Refer to the illustration courtesy of NASA/JPL/Caltech.

“This illustration of Jupiter’s moon Europa shows how the icy surface may glow on its nightside, the side facing away from the Sun. New lab experiments re-created the environment of Europa and find that the icy moon shines, even on its nightside, due to an ice glow. As Jupiter bombards Europa with radiation, the electrons penetrate the surface, energizing the molecules underneath. When those molecules relax, they release energy as visible light. Variations in the glow and the color of the glow itself could reveal information about the composition of ice on Europa’s surface. Different salty compounds react differently to the radiation and emit their own unique glimmer. Color will vary based on the real composition of Europa’s surface.”

It’s beautiful . . . but lethal to almost all life on Earth (life as we know it, that is.)  However, one form of bacteria on Earth thrives in a radioactive environment.  It’s called Desulforudis audaxviator.  It lives two miles below the ground in complete darkness without oxygen or organic compounds at a temperature of 140 degrees.  Essentially, it depends on atomic fuel to proliferate and metabolize.  This might make it ideal for the surface of Europa.  And if this life can exist under lethal conditions, maybe something else can was well?

Cynthia Phillips, a planetary geologist at NASA’s Jet Propulsion Laboratory, would be perfectly happy to find microscopic life rather than something along the lines of Godzilla.  She points out that “alien life, if it exists, is likely to be small and simple. Energy sources are limited in the Europan depths, and scientists don’t think the environment can support the development of more complex organisms. . .” 

Europa promises to be a sort of giant “petri dish” in the search for life. In some way it is close to the Earth. But given the 390,407,520 miles between Europa and the Earth which must be traveled plus the time it takes to design orbiters or landing crafts, get Congressional appropriations, etc., you may not live to learn of any startling discoveries in the decades ahead.