National Geographic Emerging Explorer Kevin Hand has traveled to Earth's extremes to better understand how life might exist in space.

Hand, the deputy chief scientist for solar system exploration at NASA's Jet Propulsion Laboratory in Pasadena, California, U.S.A., has spent time on Battleship Promontory, Antarctica, traveled far north to Barrow, Alaska, and been deep in the Mid-Atlantic Ridge. If life can exist in these frigid places, he reasons, it might also exist on Jupiter's moon Europa or Saturn's moon Enceladus, for example.

"One big-picture aspect is understanding the constraints of habitability for life as we know it," Hand says. "So we study and understand the limits of habitability here on Earth, so that we can better identify and explore potentially habitable environments elsewhere, whether that's Europa or Mars or Enceladus."

But even a cold day in Antarctica doesn't reach the temperature of Europa, at -173 degrees Celsius (-280 degrees Fahrenheit).

"No place on Earth compares to the surface of Europa," Hand says.

So scientists are hoping to study the moon up close. NASA is currently planning a mission to Europa and three other moons of Jupiter. Hand helps design spacecraft and equipment for the mission, and he tests some early versions of these tools in Earth's extreme regions.

"When we go out into these environments, we also use some of the tools and techniques that are being developed or deployed on the spacecraft, and that will provide the data for us when we land rovers and spacecraft on these worlds," he says. "The approach is sort of twofold from understanding the limits of life on Earth and understanding how to utilize the techniques and technology to study that life both here and beyond."

Lost City

One of Hand's most fruitful expeditions found him in the middle of the Atlantic Ocean. Hand descended in a submersible to investigate a unique underwater feature known as the "Lost City." The "city" is actually a collection of carbonate towers that looks like a cathedral. Carbonate is a material produced as seawater interacts with vent fluid ejected by the region's hydrothermal vents.

More than a kilometer beneath the surface of the ocean, where light does not reach, bacteria in Lost City cannot use photosynthesis to create energy. They use a process called chemosynthesis, which uses materials found in vent fluid.

Hand believes places like Lost City can provide valuable clues about how life might exist on Europa. The moon is covered in ice, and scientists think there is a liquid ocean beneath its crust. Light, and therefore photosynthesis, would not be available to life on Europa. "The exciting aspect of hydrothermal vents in the context of astrobiology is that there are ecosystems operating independently or not directly powered by photosynthesis," he says. "They are utilizing chemosynthesis at the base of the food chain."

Places like Lost City also help Hand determine where to begin looking for life on Europa.

"If Europa is being tugged and pulled and squeezed through the tidal interaction with Jupiter, then there's good reason to believe that the seafloor of Europa might be somewhat active and may host some hydrothermal vents," he says. "And if Europa has hydrothermal vents, that's a great place for providing the chemistry needed for life. So those would be the types of environments that we would want to go and explore."

Extraterrestrial Oceans

The possibility of liquid oceans on Europa and Enceladus has spurred scientists to focus on the two moons in their search for life in space.

"If we have learned anything about life on Earth," Hand says, "it's that where you find water, you generally find life."

Hand believes Europa holds the best possibility of life.

"When we think of priorities of next missions, I champion Europa because I think the science of Europa is mature," he says. "We understand Europa quite well in terms of the geophysical models and the reason why it has an ocean."

Hand says Europa seems to have a lot of water, despite its relatively small size.

"Europa is quite a bit smaller than the Earth, but the 100-kilometer [60-mile]-deep liquid water ocean ends up containing two to three times the volume of all the liquid water on Earth," he says.

Even if NASA launches a probe to Europa in 2020, it would take another eight years for the spacecraft to reach the moon. But Hand puts the seemingly long wait into perspective.

"When you think about it on our day-to-day scale, it seems like a long time," he says. "But when you think about the history of humanity and how long humans have been asking this question, it's really the blink of an eye. It's quite exciting that I'm alive during the time period when we have the technological capability to go out and not just ask these questions but also potentially answer them."