The prospects for finding life beyond Earth may be brightening. Today, scientists are reporting evidence for yet another potential habitat in our solar system: Saturn’s moon Enceladus. Scientists mining new data from the Cassini spacecraft say they may have found evidence that Enceladus—the planet’s fourth-largest moon—hosts liquid water.
If the results hold up, this would bring to four the number of bodies in the solar system—including Earth—that display active volcanism. And since life as biologists know it requires liquid water and a source of energy, Enceladus would join Jupiter’s moon Europa and Saturn’s moon Titan, as well as Mars, as possible spots beyond Earth where simple forms of life may have gained or still maintain a foothold.
The discovery, however, is bittersweet for many scientists. NASA’s proposed budget for fiscal 2007 calls for a 50 percent cut in its astrobiology program. Although the program is a tiny piece of the agency’s overall spending plan for science, it’s a significant source of money for probing fundamental questions of how and why life emerged on Earth and whether life arose elsewhere in the universe.
A 50-percent cut "is almost a going-out-of-business-level cut" in a vibrant line of research that stands as one pillar supporting President Bush’s vision for space exploration, says planetary scientist Sean Solomon, who heads the Department of Terrestrial Magnetism at the Carnegie Institution of Washington.
Nevertheless, the research in today’s issue of the journal Science is the sort of thing that continues to light a fire under the field. Its report about liquid water under the icy surface of Enceladus is a "radical conclusion," acknowledges Carolyn Porco, who leads the imaging team working with data from the Cassini orbiter. But if the team is right, "we have significantly broadened the diversity of solar-system environments" that might have rolled out the welcome mat "for living organisms," she concludes. Images released last fall show the moon ejecting vast plumes of material near its unexpectedly warm south pole. As the team pondered the evidence, they nixed several explanations, including the idea that the particles in the plumes were driven by vapor billowing out as ice reached the surface and immediately turned into a gas. The last idea standing: Liquid water was venting from reservoirs near the surface, perhaps only tens of meters below the frigid crust. This explanation also helped solve the riddle of puzzlingly high levels of oxygen atoms found in Saturn’s neighborhood.
Confirmation could come with additional flybys. If water—and perhaps life—is present, it wouldn’t be "luxuriant," notes Jeffrey Kargel, a researcher at the University of Arizona at Tucson. It likely would face tough conditions—nasty chemicals, very low temperatures, and little energy to drive it. still, he adds, it’s premature to cross the moon off the list of possible "outposts" for life beyond Earth. Yet the prospect of building on these results could be dimmer with the threat of budget cuts. The proposed reductions post several challenges, researchers say.
One is the loss of important financial leverage. While money for experiments and other research related to astrobiology can come from other funding agencies, such as the National Science Foundation or even the National Institutes of Health, NASA’s program often provides the crucial missing piece that turns demanding and sometimes dangerous fieldwork into exciting results.
One of the biggest successes over the program’s 10-year history has been to help revolutionize the way science is done. Answering questions about the origins of life on Earth and the prospects for life elsewhere require p collaborations. From radio astronomers to biologists and geologists studying the evolution of Earth, groups are working together in ways they never thought of a decade ago, adds Edward Young, a geochemist at the University of California at Los Angeles.
"NASA’s made a lot of progress by making a relatively small investment in a way that has brought disparate experts together from the whole spectrum of physical and biological sciences. It’s a wonderful lesson on how to make progress by crossing these boundaries," Dr. Solomon says. "It would be regrettable to stop that experiment. \
According to the passage, simple forms of life might be found on the following heavenly bodies in the solar system: ______.
A．Europa, Titan, Earth’s moon and Mars
B．Europa, Mars, Titan and Enceladus
C．Jupiter, Saturn, Mars and Enceladus
D．Earth’s moon, Jupiter, Mars and Saturn
