ALL THESE WORLDS ARE YOURS, EXCEPT...

" . . . relay this information to Earth. Tsien destroyed three hours ago. I'm only survivor. Using my suit radio – no idea if it has enough range, but it's the only chance. Please listen carefully. THERE IS LIFE ON EUROPA. I repeat: THERE IS LIFE ON EUROPA. . . "
~ 2010: Odyssey Two by Arthur C. Clarke

Europa, one of the Jupiter's large moons, holds a special place in the minds of science fiction writers and astrobiologists alike. What sets Europa apart from the other planets and moons in our solar system is that it is covered with a fairly smooth surface layer of frozen water, and its interior is much hotter than its surface, suggesting that there could be a zone of liquid water under that protective layer of ice where life might exist. That easily accessible source of water on its surface could also make Europa a handy refueling stop for space ships exploring the outer solar system – assuming there isn't the sort of life that destroyed the ill-fated spaceship Tsien in Clarke's 2010.

In the afterword to 2010, Arthur C. Clarke says his Europans were inspired in part by a 1980 article by Richard C. Hoagland – "The Europa Enigma" – which describes his "quite brilliant concept" that there might be life on Europa. Since then, NASA's Galileo exploration mission to Jupiter and its moons has provided more detailed information about the moon's surface:

Prior to the Galileo mission, scientists' knowledge of Europa was simply a small ice- covered moon with an exceptionally bright surface covered by faint curved and linear markings. Now, scientists see evidence of a young and thin, cracked and ruptured ice shell, probably moving slowly over the surface of a briny ocean that is 100 kilometers (62 miles) or more deep.

University of Arizona Professor of Planetary Sciences Richard J. Greenberg, a member of the Galileo Imaging Team, believes that Europa might even be able to support fairly complex life forms, as Discovery News reported last week:

Judging by how quickly Europa's surface ice is replenished, Richard Greenberg estimates that enough oxygen reaches the subterranean ocean to sustain "macrofauna" -- more complex, animal-like organisms. Assuming Europa life forms would need as much oxygen as Earth-like fish, Greenberg estimates the moon's ocean has enough oxygen to support 6.6 billion pounds of macrofauna.

Unconstrained by the limitations of biology, futurist/physicist Freeman Dyson has speculated a bit more wildly, suggesting that we should be looking for flowers on Europa's surface:

Life could be visible from orbiting spacecraft, however, if it made a home in cracks in Europa's shell that connect the surface to the interior, Dyson said.

Such life might take the form of flowers with a parabolic shape that focuses the dim sunlight falling on Europa on the interior of the plant. Flowers with such shapes [...] are found in Arctic climes on Earth, where the plants have evolved to maximise solar energy.

Europa flowers could be detectable through a phenomenon called retroreflection, in which light gets reflected back to its source, Dyson said. This optical effect is seen in light reflected from animals' eyes, and was used in the design of road signs and mirrors left behind on the moon by Apollo astronauts.

My first thought was that Dyson had wandered off into Larry Niven's Known Space, but on further consideration I think it's an interesting idea – assuming that Dyson was referring to life forms with a superficial resemblance to flowers, rather than actual Earth-type plants. Or as University of Washington astrobiologist John Baross explained:

As for Dyson's flower suggestion, he says it is "a very radical" idea. "On Earth, flowering plants evolved during the Cretaceous and became diverse by co-evolving with insects. . . . I would not include flowering plants to my list of life-forms to look for."

"Any photosynthetic system on Europa would have to live at a depth removed from the high radiation bombarding the ice surface and still get light," Baross says. "Having said this, it would be worthwhile to make more comprehensive observations and analysis of some of the surface features, including the deeply coloured ridges [...]," he says. "One might find evidence for biosignatures or very interesting chemistry."

More likely than surface flowers are organisms similar to those found around the deep sea hydrothermal vents on Earth. Frank Carsey and his colleagues at the Jet Propulsion Laboratory are designing robotic vehicles that will be able to cut through ice and explore the watery world beneath, initially in Antarctica, but with the hope of eventually exploring Europa's depths. Until we are able to send exploratory probes, the possibility of life on Europa is little more than educated speculation.


Free Short Fiction:

• "A Spy in Europa" by Alastair Reynolds
• "The Color of Sunfire" by Larry Niven (set in Know Space, with Slaver Sunflowers)

Further Background Reading:

• Scans of Richard Hoagland's article "The Europa Enigma" (Star and Sky Magazine, Jan. 1980)
• Discovery Channel Video: Top 5 Reasons Europa Rocks
• Technical Presentation: "Checking up on Arthur C. Clarke: The next mission to Europa and the Jupiter System" by Dr. Bill Moore
• University of Arizona's Richard Greenberg has written two popular science books about Europa. His most recent is Unmasking Europa: The Search for Life on Jupiter's Ocean Moon (affiliate link to Amazon.com)
• 2010: Odyssey Two (affiliatelink to Amazon.com)

Top Image: The Conamara Chaos. "a view of a small region of the thin, disrupted ice crust in the Conamara region of Jupiter's moon Europa showing the interplay of surface colors with ice structures." From NASA's Galileo Image Gallery. More details.
Middle Image: Europa and the Thrace Region. This image shows an image of the cracked surface of Europa. From NASA's Galileo Image Gallery.
Middle Image:"Metal Flower" http://www.flickr.com/photos/quepollo/ / CC BY 2.0
Bottom Image: Artist's concept of a cryobot and hydrobot that can melt through ice and then explore the water beneath. From "The Search for A Planetary Ocean on Europa" at JPL.
Tags:science fiction, biology, Europa