Thursday, August 31, 2006


Jupiter Moon May Have Life -- Experts Urge a Mission

John Roach
for National Geographic News

Scientists say Jupiter's moon Europa rivals Mars as a potential refuge for life. Some of them are now urging NASA to explore the ice-covered satellite.
"It takes longer to get there [than to get to Mars], it's more expensive, and a bigger deal to plan a mission. But if I had a choice, I'd go for Europa," said Lynn Rothschild, an astrobiologist with the NASA Ames Research Center in Moffett Field, California.
Rothschild studies the origins of life on Earth and other planets. She's intrigued by Europa because it appears to contain likely key ingredients for life—water, an energy source, organic compounds, and billions of years of development.
Taken together, these ingredients are sufficient to support life, scientists say. To answer the question of whether life actually exists on Europa, however, requires further exploration with orbiters and landers like those currently exploring Mars. (See picture of and news about Mars's newfound "frozen sea.")
"The big unknown is what's needed for life to originate," said Robert Pappalardo, a planetary scientist and expert on Europa at the University of Colorado at Boulder.

Life Ingredients

Europa is roughly the size of Earth's moon but is otherwise markedly different. To begin with, at 490 million miles (790 million kilometers) from the sun, Europa's surface is a bone-chilling –230° Fahrenheit (–145° Celsius). That's much too cold to support life as we know it.
But scientists believe the interior of Europa is heated by tidal flexing, a process that results from the gravitational tug-of-war among Jupiter and its moons. The heating may be sufficient to keep the inner layers liquid.
The Galileo spacecraft beamed close-up images of Europa's surface to Earth in the late 1990s and early 2000s. The images revealed patterns of ridges and cracks in the crust that are suggestive of an icy shell moving over a liquid ocean, scientists say.
Scientists are uncertain if Europa has organic compounds. Galileo, though, did detect carbon dioxide, sulfur dioxide, cyanogens (colorless, poisonous, flammable gases), and hydrocarbons (hydrogen-carbon compounds often found in natural gas and petroleum) on neighboring moons Callisto and Ganymede.
"It all suggests there is energy, water, and possibly organics, and so it starts to get very exciting," Rothschild, the NASA astrobiologist, said.
Another possibility is that hydrothermal vents, like those at the bottom of the Earth's oceans, are spewing energy and chemicals into Europa's ocean. If so, such vents could be a refuge for life, Pappalardo said.

Europa Missions

In September 2003, after eight years in orbit, the Galileo spacecraft was purposely sent into Jupiter's atmosphere, where it would burn up. The maneuver prevented the spacecraft from crashing into Europa and potentially contaminating the icy moon with microbes that might have hitchhiked from Earth.
"I'm delighted I'm a biologist and not a planetary scientist," Rothschild said. "There's not a whole lot of new data since Galileo. People are combing over the past data, but what we need is a mission."
Pappalardo said he and his colleagues have recently used Galileo's data to build better models of Europa. These models demonstrate the evidence for a salty ocean, the active surface geology, and even the estimated maximum thickness of the icy surface—about 12 miles (20 kilometers).
But Pappalardo is yearning for new data. He was one of 80 U.S. planetary scientists who signed a report in January urging NASA to make a mission to Europa a priority.
The U.S. space agency has tentative plans to launch the nuclear-powered Jupiter Icy Moons Orbiter in 2015, four years later than originally planned. Technical challenges may further delay or entirely scrap the mission.
"Europa is such a high priority for exploration that it shouldn't wait," Pappalardo said.
Putting off a mission to Europa, he said, would be as if NASA had ruled out all Mars exploration until the agency had developed the perfect technology for bringing back a Martian soil sample—instead of proceeding with other types of Mars exploration in the meantime, as the space agency has done.
"It's the same with Europa. It's a high priority, and it doesn't seem prudent to wait for the ultimate mission when we should be doing that reconnaissance exploration in the shorter term," the planetary scientist said.
As a first step, Pappalardo said, NASA should send an orbiter to Europa to determine the characteristics of its ice shell, confirm the existence of an ocean, and analyze the chemistry of what appears to be dark organic matter on the moon's surface.
Later missions could include landers to search for life and potentially an underwater robot that could melt through surface ice to sample water below. "But that's hard to do, and it's a long time off," he said.


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