To better understand how life might exist in space, Kevin Hand is going to the extreme parts of Earth.
Hand is the deputy chief scientist for solar system exploration at NASA's Jet Propulsion Laboratory in Pasadena, California. He 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.
We need to understand the conditions in which life can take place, Hand said. By studying creatures in extreme environments on Earth, "we can better identify and explore potentially habitable environments" in other worlds.
However, even a cold day in Antarctica doesn't reach the temperature of Europa. The moon typically sits at -173 degrees Celsius (-280 degrees Fahrenheit). Scientists are therefore hoping to study Europa 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. He goes to regions on Earth with extreme climates in order to test some of these tools.
One of Hand's most fruitful expeditions found him in the middle of the Atlantic Ocean. Hand descended in a submarine 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 towers are produced when seawater interacts with fluid ejected by the region's hydrothermal vents. These vents are holes in the ocean floor, which often appear around volcanoes. The fluid contains minerals that solidify into calcium carbonate structures.
More than a kilometer (about a mile) beneath the surface of the ocean, where light does not reach, bacteria in Lost City cannot use photosynthesis. This is the process most plants above ground use to turn sunlight into energy. Instead, these underwater organisms use a process called chemosynthesis. This process 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, but chemosynthesis might.
Places like Lost City also help Hand determine where to begin looking for life. "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 said. "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."
The possibility of liquid oceans on Europa and Enceladus has excited scientists. They are focusing on these two moons in their search for life in outer space. "If we have learned anything about life on Earth," Hand said, "it's that where you find water, you generally find life."
Hand said we know the type of terrain Europa has, and why it has an ocean. He also said Europa seems to have a great deal of water, despite its relatively small size. Europa is quite a bit smaller than the Earth, he said. However, its 100-kilometer (60-mile)-deep liquid water ocean "ends up containing two to three times the volume of all the liquid water on Earth."
Even if NASA launches a spacecraft to Europa in 2020, it would take another eight years for the spacecraft to reach the moon. Still, 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 said. "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."