Under a thick crust of ice, Europa might have an ocean warmed by tidal interactions with Jupiter. This tidal flexing could also produce a geologically active core that might in turn create hydrothermal vents on the ocean floor.
Credit: NASA/JPL/Ted Stryk
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Scientists have long been intrigued by Jupiter's fourth largest moon with its underground ocean and icy shell. Researchers have said that Europa's saltwater ocean could harbor life, and some have theorized that it is the most likely place to find life in the solar system.
"[Europa] is one of the premier places to search for living life, that is, life that's alive today, life that we can poke and prod at and ask this fundamental question of what makes it tick," said Kevin Hand, the deputy chief scientist of solar system exploration at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Is its fundamental biochemistry the same as that on Earth or is it different? Is the origin of life easy or hard? There are all questions that Europa could potentially answer." [See Photos of Europa, An Icy Moon of Jupiter]
Unmanned robotic landers, deep space probes and even manned missions could help researchers answer some of those outstanding questions.
Scientists know that Europa is covered in a shell of ice, and data suggest that an ocean of liquid water also lurks below the surface. Some hope to send a submersible with the ability to dive beneath the ice to explore Europa's salty interior.
Building a submersible
In 2011, NASA awarded Stone Aerospace $4 million to continue the development of its "cryobot" project designed to autonomously explore the ocean of the moon.
"When we speak of the Europa mission at our shop we are talking about going for the gold ring: landing on the surface of Europa; sending a nuclear-powered cryobot carrier vehicle through the ice crust; discharging a nuclear-powered 'fast mover' autonomous underwater carrier vehicle that has planet-scale range, and selectively launching a series of miniaturized, highly intelligent AUVs [Autonomous Underwater Vehicles] to go into the more dangerous areas (e.g. around black smokers, up into ice cracks, into corrosive chemical plumes) to search for and collect biological samples and bring them back to the mother ship," Stone Aerospace CEO Bill Stone wrote told SPACE.com in an email.
Ideally, the robotic instruments included with the lander would come equipped with life-detecting instrumentation. [Europa Report: Jupiter's Icy Moon Explained (Infographic )]
Scientists are getting closer to developing viable versions of these scientific instruments that could travel to Europa, Stone said.
"The U.S. science community is today, thanks to NASA funding, on the verge of having available portable molecular DNA sequencers that could allow a Europa AUV to characterize life found on Europa at the microbial scale and then to return to the cryobot and uplink the information to the lander and back to Earth," Stone said.
Flybys and remote sensing
Scientists can also learn about Europa through remote sensing, using spacecraft flybys of the moon like NASA's Galileo spacecraft did after it arrived at Jupiter in 1995.
"There's a vast array of things you can learn from satellite observations of a planet," said Jeffrey Plaut, a NASA scientist at JPL. "If you're talking about Europa specifically, the science objectives have been laid out pretty clearly over the years for various space-born observations of Europa. Some very fundamental things like: How thick is the ice shell? Where is the ocean?"
Plaut hopes to use radar to investigate some of these questions when the European Space Agency's JUICE (short for JUpiter ICy moons Explorer mission) spacecraft launches. The spacecraft is expected to launch in 2022 and arrive at Jupiter in 2030. JUICE will make a flyby of Europa twice and explore other moons in the Jupiter system
Landing on Europa
Traveling to and landing on Europa could present unique challenges.
At the moment, scientists aren't precisely sure what the surface of the moon looks like. Some researchers have theorized that the moon's equator harbors spikes of ice, and it's possible that the outer shell of the planet shifts, making it even more difficult to understand where a lander should be set down.
The landing itself could also be a difficult prospect. While scientists in charge of the Curiosity rover on Mars experienced "7 minutes of terror" during the robot's sky crane descent to the Red Planet, landing a probe on Europa could be more panic-inducing.
Engineers would experience "one and a half hours of terror" because of the moon's distance from Earth, Hand told SPACE.com.
"On Europa there is no atmosphere, and that's bad because you can't use a parachute to slow down. It's good because it means that your spacecraft can, for the most part, do a pinpoint landing once it finds a safe spot to land." Hand said. "The lander would have to have some intelligence onboard to allow it to navigate even in the best-case scenario of us having imagery from a prior mission."
Imagining a Europa mission
The minds behind the science fiction movie "Europa Report" aren't waiting for another mission to launch before bringing their vision of the moon to the big screen.
Set to hit theaters on Aug. 2, the movie chronicles the fate of the fictional crew of the first manned mission to Europa. The story unfolds through postmortem interviews that reveal what happened as the crew traveled to and landed on the moon.
The filmmakers set out to make the most realistic depiction of the world they could, asking Hand to consult with them on the scientific aspects of the movie before its release.
"It makes all the difference when the science and some of the aspects of the natural environment are in and of themselves a character in the movie," Hand said. "Perhaps most importantly and most exciting about the movie from my perspective is their portrayal of scientists I think is quite accurate and engaging."