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(CNN)Ocean worlds in our solar system are attractive places in the search for life beyond Earth.
Beneath a thick, icy shell, Jupiter's moon Europa and Saturn's moons Titan and Enceladus likely harbor oceans, scientists believe. On Earth, the oceans teem with life, but is the same scenario possible on these frosty moons?
Future missions could reveal if ocean worlds are habitable, and if so, what kind of life could exist below the ice. Orbiters such as NASA's Europa Clipper and the European Space Agency's Jupiter Icy Moons Explorer will fly by Europa this decade, and a rover-size drone called NASA's Dragonfly will launch in 2027 to reach Titan in the 2030s.
Scientists who authored the 2022 planetary decadal survey have recommended sending the Orbilander mission to Enceladus, which would both orbit and land on Saturn's tiny moon in the 2050s.
But exploring the challenging terrain as well as the oceans themselves may require technology that seems more like science fiction.
Here are some of the concepts experts are exploring at NASA's Jet Propulsion Laboratory in Pasadena, California, that could one day transform into a mission diving beneath the ice on alien worlds.
Little is known about the frozen terrain covering Europa and Enceladus, so any mission exploring the surface of these worlds could potentially have to navigate treacherous landscapes.
A concept called SPARROW, or the Steam Propelled Autonomous Retrieval Robot for Ocean Worlds, would be able to hop right over any hazards such as long ice blades called penitentes.
"The terrain on Europa is likely highly complex," said Gareth Meirion-Griffith, JPL roboticist and lead researcher of the concept, in a statement. "It could be porous, it might be riddled with crevasses, there might be meters-high penitentes that would stop most robots in their tracks. But SPARROW has total terrain agnosticism; it has complete freedom to travel across an otherwise inhospitable terrain."
The concept includes a lander that acts as a home base for a spherical robot. This ball, which resembles a cage and is about the size of a soccer ball, would include instruments and thrusters.
Rather than relying on fuel, the SPARROW ball would use steam created from melting ice. The low gravity on ocean worlds would allow the ball and its steam-powered thrusters to hop for miles.
The lander would collect and melt the ice, then load water into SPARROW. The robotic ball's engines could warm the water to create a steam boost.
Instruments aboard SPARROW could be used to collect samples that could be analyzed on the lander.
And more SPARROWs may be better than one to explore these mysterious, distant worlds.
Since 1997, scientists have used rovers to study Mars and uncover intriguing details about its habitability in the past.
The Buoyant Rover for Under-Ice Exploration, or BRUIE, would act in much the same way -- just inside an ocean on Enceladus or Europa, rather than on land.
A rover exploring an ocean world will need to navigate on its own. The BRUIE prototype is about 3 feet (1 meter) long and has two wheels to help it roll upside down along ice. Images and data collected by the floating rover will allow scientists to study the "ice-water interface."
"We've found that life often lives at interfaces, both the sea bottom and the ice-water interface at the top. Most submersibles have a challenging time investigating this area as ocean currents might cause them to crash, or they would waste too much power maintaining position," said Andy Klesh, lead engineer for the concept, in a statement.
"BRUIE, however, uses buoyancy to remain anchored against the ice and is impervious to most currents. In addition, it can safely power down, turning on only when it needs to take a measurement, so that it can spend months observing the under-ice environment."