In the discussion about the possibility of finding extraterrestrial life, Mars usually gets all of the hype. As our closest neighbor, it would seem likely that the Red Planet could be capable of supporting some simple single-celled organisms, perhaps tucked away under its polar ice caps.
But many scientists are now searching for life in a rather unlikely place: Jupiter's icy moon, Europa.
Only slightly smaller than Earth's moon, Europa is the second-closest to its mother planet. Fly-bys from past satellite missions have revealed images suggesting that it has a crust consisting primarily of ice with vast oceans of liquid water, larger than those on Earth, lying beneath the surface.
"Mixing into the ocean of material from the surface ice shell above, and from an active sea-floor below, may provide sources of energy that could support life," said Andrew Cheng, chief scientist of the Space Department at Hopkins' Applied Physics Laboratory (APL).
To that end, NASA and the European Space Agency (ESA) are teaming up for the Europa System Jupiter Mission, which is scheduled to launch in 2020 and will focus on the exploration of Europa, using NASA's Jupiter Europa Orbiter, and Ganymede, Jupiter's largest moon, with ESA's Jupiter Ganymede Orbiter.
Additionally, the Russian Federal Space Agency has also expressed interest in contributing a "Jupiter Europa Lander" to the mission, which could potentially obtain samples of Europa's surface and drill through to the ocean below to gather information which would then be sent back to Earth.
Back at Hopkins, APL has been heavily involved in past missions that explored Europa and its neighbors, providing much of the hardware, data analysis and instrumentation. "APL was involved in the many robotic spacecraft missions that flew past Jupiter, [including] Voyager 1 and 2, Ulysses, Cassini [and] New Horizons, and an orbiter, Galileo," Chris Paranicas said, who was a lead APL scientist for the Galileo mission and a member of NASA's science definition team for the Europa mission.
Galileo was the first spacecraft ever to orbit Jupiter, and, through fly-bys of Europa, it provided much of what we now know, including magnetic measurements indicating the presence of a salty ocean.
The Galileo mission ended almost exactly six years ago when, on a nearly empty fuel supply, it was commanded to crash into Jupiter to prevent any future impact with and contamination of Europa.
The Cassini spacecraft was able to provide further information on Europa's atmosphere.
"On its way to Saturn, Cassini flew by Jupiter, and, using an imaging technique that APL invented, our instrument was able to image extended gases around Jupiter that are created by the radiation impacts on Europa's surface," said Barry Mauk, the group supervisor for APL's Space Physics Group.
Some of these gases include oxygen, which is generated not from biological processes, as on Earth, but from collisions between charged particles which have been emitted from Jupiter's magnetic environment and the moon's icy surface, and which break water molecules into oxygen and hydrogen. But don't expect to be able to take a breath of fresh air there, because the atmospheric pressure is one trillionth that of Earth's.
Sure, you might be thinking, there's a bit of water, but nothing could possibly survive on a moon that's five times the Earth's distance from the Sun, which would lend to an environment that's quite a bit colder.
However, new discoveries suggest that wherever liquid water exists, there is potential for life.
"This thinking is driven by?the multiple discoveries at Earth of so-called "extremophiles" - living microbes and creatures that can live at temperatures that nearly span the extremes of temperatures that can be found at Earth," Mauk said.
Furthermore, the pull of Jupiter's gravitational force on Europa creates tides in its submerged seas, which in turn generate friction and therefore heat. This could make the interior of the planet significantly warmer than it would otherwise be at the surface. These tides might also have the ability to create cracks in the surface of the moon, allowing life-inducing chemicals to seep through.
Combine these factors with the possibility of volcanic vents on the ocean floor, spitting out chemicals and energy, and you have a potential recipe for complex organisms.
However, getting to Europa in the first place will be a monumental task in itself.
"It is deep within Jupiter's gravity well, and a spacecraft must either orbit around Europa or land on its surface to make the required measurements," Cheng said. "There is a harsh radiation environment at Europa, which tends to degrade spacecraft electronics and instruments."
Another crucial aspect of the mission is that if a probe will be searching for life on the moon, coming up with false positives or bringing non-native particles to Europa that could potentially induce life must be avoided at all costs.
"Europa is a high priority for planetary protection, meaning that we would not like to contaminate the surface in any way with terrestrial organics," Paranicas said. "Therefore a future Europa orbiter will have to be sterilized before launch."
Additionally, with NASA slated to fund the bulk of the Europa System Jupiter Mission as well as a deep-space exploration in free-fall, it's likely that a 2020 launch date is on the highly optimistic side.
"It costs a very large amount of money just to get the spacecraft to the vicinity of Jupiter, with our limited and expensive rocket capabilities," Mauk said.
Nevertheless, NASA announced back in February that a Europa mission would take top priority for its Outer Planet Flagship Mission, beating out a competing proposal for exploration of one of Saturn's moons, Titan.
APL will be partnering with NASA's Jet Propulsion Laboratory for this upcoming project to help define the specific scientific objectives that the Europa mission should accomplish. "APL will be responsible for a portion of the spacecraft hardware, its instrument payload and its operations," Cheng said.
Although the Europa orbiter would not reach its destination until 2026 if launched on schedule, for now, this moon is our most promising lead in the search for life beyond Earth.
