At NASA’s Astrobiology Science Conference held in Atlanta last week, visionary space inventor Bill Stone announced that he intends to get an autonomous six-foot by ten inch robotic cylinder called Valkyrie ready to visit the icebound sea of Jupiter’s moon Europa, cut through the icy crust, explore the waters below, and collect samples in the search of life. in 2011, Stone announced that NASA awarded his venture, Stone Aerospace, a four-year, $4M funding to continue development of the Valkyrie project, to design and field-test an autonomous ice penetrating cryobot.
Stone is not alone in his belief that Jupiter's Europa might not only sustain, but foster life. The University of Arizona's Richard Greenberg, a professor of planetary sciences and member of the Imaging Team for NASA's Galileo Jupiter-orbiter spacecraft is also an ardent champion of Europa as a potential hotspot for the discovery of life beyond Earth.
Europa, similar in size to Earth's moon, has been imaged by the Galileo Jupiter-orbiter spacecraft. Its surface, a frozen crust of water, was previously thought to be tens of kilometers thick, denying the oceans below any exposure. The combination of tidal processes, warm waters and periodic surface exposure may be enough not only to warrant life, but also to encourage evolution.
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."
Tides have created the two types of surface features seen on Europa: cracks/ridges and chaotic areas, Greenberg said.The ridges are thought to be built over thousands of years by water seeping up the edges of cracks and refreezing to form higher and higher edges until the cracks close to form a new ridge.
The chaotic areas are thought to be evidence of the melt-through necessary for exposure to the oceans.
The tidal heat, created by internal friction, could be enough to melt the ice, along with undersea volcanoes - a combination of factors would give organisms a stable but changing environment -- exactly the type that would encourage evolution.
As a prelude to a future Europa robotic mission, Stone intends to test a working cryobot at Alaska’s Matanuska Glacier in June next year, where it will attempt to cut through ten to fifty meters of ice. Afterward the cryobot will try to get through 200 meters in Greenland, in fall 2014.
A manned mission to Europa has some huge obstacles right off the launching pad: first, it will take about five years to reach the satellite, with the same amount of time being required for the return journey. Second, Jupiter's radiation would mean that any trips beyond a thick set of shielding would be deadly. A 2011 report in Wired outlined the potential hazards for Stone's robotic mission, including solar power being unable to work below the surface; batteries not lasting long enough; too large a footprint of a device; and international treaty restrictions that would forbid testing of a nuclear robot.
Astronomers believe, based on images from the Galileo mission and magnetometer readings, that Europa has an icy shell over a liquid ocean, with a solid rocky core at the centre. There’s some disagreement between scientists on how thick the ice is — estimates range from 10 to 100,000 metres — but observations have yielded reports of a number of “double-ridges” on the surface that are believed to be cracks in the crust caused by huge gravitational forces — the Jovian equivalent of tides on Earth, but amplified many times due to Jupiter’s considerably-greater mass. Once a crack forms, it gets squeezed back together and pulled apart again every time the moon rotates, which is approximately once every three and a half Earth days.
The cracks are the most likely place for life to take root. They get sunlight (unlike the rest of the ocean below the ice) and are also subjected to strong currents.
Plans to investigate Europa's cracks-likely to be the largest energy sources available to any life that exists on the planet- is right on the mark. A probe would enter orbit around the moon, scanning for these double-ridges.
Europa's extraterrestrial ocean is currently being fed more than a hundred times more oxygen than previous models had suggested --enough to support more than just microscopic life-forms: At least three million tons of fishlike creatures could theoretically live and breathe on Europa, Greenberg concluded.
Image credit: Stone Aerospace