Jupiter's Europa might not only sustain, but foster life, according to the research of University of Arizona's Richard Greenberg, a professor of planetary sciences and member of the Imaging Team for NASA's Galileo Jupiter-orbiter spacecraft. The deepest ocean on Earth is the Pacific Ocean's Marianas Trench, which reaches a depth of 6.8 miles awesomely trumped by the depth of the ocean on the Jupiter's moon, Europa, which some measurements put at 62 miles. Although Europa is covered in a thick crust of scarred and cross-hatched ice, measurements made by NASA's Galileo spacecraft and other probes strongly suggest that a liquid ocean lies beneath that surface. The interior is warmed, researchers believe, by the tidal stresses exerted on Europa by Jupiter and several other large moons, as well as by radioactivity.
With Jupiter being the largest planet in the solar system, its tidal stresses on Europa create enough heat to keep the water on Europa in a liquid state. More than just water is needed to support life. Tides also play a role in providing for life. Ocean tides on Europa are much greater in size than Earth's with heights reaching 500 meters (more than 1,600 feet). Even the shape of the moon is stretched along the equator due to Jupiter's pull on the waters below the icy surface.
The mixing of substances needed to support life is also driven by tides. Stable environments are also necessary for life to flourish. Europa, whose orbit around Jupiter is in-sync with its rotation, is able to keep the same face towards the gas giant for thousands of years. The ocean is interacting with the surface, according to Greenberg, and "there is a possible that extends from way below the surface to just above the crust."
"The real key to life on Europa," Greenburg adds, "is the permeability of the ice crust. There is strong evidence that the ocean below the ice is connected to the surface through cracks and melting, at various times and places. As a result, the , if there is one, includes not just the liquid water ocean, but it extends through the ice up to the surface where there is access to oxidants, organic compounds, and light for photosynthesis. The physical setting provides a variety of potentially habitable and evolving niches. If there is life there, it would not necessarily be restricted to microorganisms."
Europa has long been considered a potential hotspot for life in the Solar System. NASA's Astrobio.net reports that one of the first visitors to Jupiter's icy moon of Europa could be a tiny submarine barely larger than two soda cans. The small craft might help strike the right balance between cost and capability for a robotic mission to look for alien life in the ocean beneath Europa's icy crust.
The idea for the incredible shrinking submarine originally came from NASA’s Jet Propulsion Laboratory (JPL) in California and Uppsala University in Sweden. Such a vehicle (image below) would help keep mission costs low at a time when launching objects into space can still cost tens of thousands of dollars per kilogram. The mission concept also would have the advantage of only requiring a small borehole drilled through the ice covering Europa's surface.
"What I think is exciting with this is to be able to explore previously inaccessible areas, to explore where no "man" has explored before," said Jonas Jonsson, an engineer now with Stinger Ghaffarian Technologies Inc. at NASA Ames Research Center in Moffett Field, Calif.
A paper study of the miniature submersible first came from NASA JPL researchers and Greger Thornell’s Swedish team at Angstrom Space Technology Centre of Uppsala University. But Jonsson, an original member of the Swedish team, refined the submersible concept by building and testing parts of it for his Ph.D. thesis.
Scientists have gravitated toward the possibility of life on Europa ever since the Voyager 2 mission first scouted out the icy moon from afar in 1979. Voyager 2's images and data hinted at the existence of a liquid water ocean lurking beneath Europa's icy surface — a huge body of water bigger than all of Earth's oceans combined.
The existence of Arctic bacteria living under extreme frigid conditions on Earth suggests that life could possibly survive on icy Europa as well. But any life on Europa would only survive by hiding deep beneath Europa's crust — an icy covering about several kilometers (1 or 2 miles) in thickness — because of the radiation from Jupiter's magnetosphere bombarding the moon's surface.
Such intense radiation means a robotic lander digging a few feet into Europa's icy surface would likely find no organic traces or signs of life. Instead, a robotic mission might have better luck by going deep beneath the icy crust to study Europa's ocean.
Jonsson envisions the tiny submarine named Deeper Access, Deeper Understanding (DADU) taking on the Europa challenge in his 2012 Ph.D. thesis for Uppsala University in Sweden. The submarine could first get its feet wet by exploring similar watery environments on Earth where its small size could prove exceptionally useful.
"A mission to explore Lake Vostok in Antarctica, which is believed to have been isolated from the rest of the world by kilometers of thick ice for millions of years, would of course be the 'Holy Grail' mission, and a real proof of concept for a future mission to explore the oceans thought to exist underneath some of the frozen moons in the solar system, such as Europa and Enceladus," Jonsson explained.
The DADU submersible would use eight small thrusters to maneuver around the underwater world. A fiber optic tether would connect DADU to a surface lander or station — a way to recharge the submersible's lithium-ion batteries and allow for remote control by a human operator. On-board software would allow the submersible to automatically dodge obstacles or stay at a certain depth underwater.
A model of Europa's interior, including a global ocean. If a 100 kilometer-deep ocean existed below Europa’s ice shell, it would be 10 times deeper than any ocean on Earth and would contain twice as much water as Earth's oceans and rivers combined. Credit: NASA/JPL
The Swedish team created a series of miniaturized instruments and sensors for the dream submersible. DADU has a forward-looking camera with a small laser to capture high-resolution video and to gauge the distance, size and shape of underwater objects.
But a huge challenge came from shrinking everything down to incredibly small sizes. The sensor for measuring the conductivity, temperature and depth of water is smaller than a fingernail.
The submersible's sonar device alone could fit within a matchstick box, Jonsson said. Such a device uses piezoelectric material that can vibrate to create acoustic sonar pulses and read reflected pulses or vibrations as electrical signals.
Jonsson also tested the idea for the submersible's sampling device for collecting tiny life forms on Europa — a microfluidic device smaller than a human thumb with a special filter to trap tiny microorganisms.
The first prototypes of the DADU submersible were made of plastic from 3D printers that allowed the team to quickly "print" the digital designs into real objects. But they envision the real submersible being built from a titanium alloy in order to survive the harsh temperatures and intense pressures of underwater environments.
Next up, the Swedish team hopes to further refine the miniaturized instruments. They also need to build the full integrated systems with all the miniaturized electronics before they can seriously test the submersible's capability to survive in a frigid ocean — whether on Earth or on Europa.
"I don’t think there are any particular technological breakthroughs required," Jonsson said. "There exist possible solutions for the technological barriers; however, further developments and optimizations are required for such a mission to succeed."
Getting down beneath the ice is still far from simple. Any Europa mission designed to penetrate the moon's icy surface would require a mole-like drill to melt its way through the ice. The submersible would also need kilometers of tether connecting it to a surface lander or station in order to communicate with its remote human operator.
Nobody is seriously planning a landing mission on Europa yet. But the European Space Agency aims to launch its JUpiter ICy moons Explorer mission (JUICE) to make the first thickness measurements of Europa's icy crust starting in 2030. NASA also has begun planning a Europa Clipper mission that would study the icy moon while doing flybys in a Jupiter orbit.
The Daily Galaxy via NASA and Astrobio.net