PROVIDENCE, R.I., March 2 (UPI) _ New pictures of the surface of Europa, one of the moons of Jupiter, show evidence of an ocean of slush just below its icy crust, suggesting that it has all the basic building blocks for life. The researchers say the new images taken by the Galileo spacecraft in December, 1997, portray a chaotic landscape littered with structures that look like icebergs and gaps between the large continent- sized ice plates.

New Photos Back Theory Of Slushy Jovian Moon

By Kathy Sawyer Washington Post Staff Writer Tuesday, March 3, 1998; Page A07

The most detailed images ever taken of Jupiter's moon Europa provide fresh evidence that the frozen surface of this ice world hides a warmer ocean of slush, or water, that could harbor life, scientists reported yesterday.
NASA's spacecraft Galileo last year produced dramatic pictures of 300-foot-high icebergs that had drifted and turned in unseen currents, as well as other evidence confirming what scientists had long suspected: that a vast ocean once flowed beneath Europa's hard, bright surface. The lingering question was whether that hidden sea had since frozen solid. The latest close-up images -- up to 20 times more detailed than the last -- are enough to convince at least some scientists it has not, though others still have questions that might be answered only by planned future missions to Europa.
"I'm confident there's liquid water at depths below the surface," said Galileo imaging team scientist James W. Head III, a planetary geologist at Brown University in Providence, R.I., where the latest images were released. "The question is how deep." The images -- taken by Galileo in mid-December -- contain three key lines of evidence from three different geological environments at three different spots on the moon's surface. Taken together, he said, they support the hypothesis that Europa is slushy just beneath its thin icy crust, and possibly even warmer at greater depths.
The moon's combination of "interior heat, liquid water, and infall of organic material from comets and meteorites means that Europa has the key ingredients for life," Head said. "Europa, like Mars and the Saturn moon Titan, is a laboratory for the study of conditions that might have led to the formation of life in the solar system." Europa is slightly smaller than Earth's moon, but many times brighter, with a surface temperature of minus 260 degrees Fahrenheit -- frigid enough to hard-freeze a primordial ocean over several million years. But scientists have proposed that Europa's gravitational tug of war with Jupiter and neighboring moons -- causing tidal bulging -- generates enough heat to keep large parts of its subsurface ocean thawed.
The ice world has intrigued scientists since the twin Voyager spacecraft conducted the first close reconnaissance of the Jupiter system in 1979. The latest images, which show truck-sized objects on the surface, are hundreds of times more detailed than the best Voyager images and between three and 20 times more detailed than Galileo's earlier Europa pictures. The key pieces of new evidence, as presented by the Galileo researchers, are:
A relatively recent impact crater where a meteorite slammed into Europa and threw up dark debris from deep down. The images indicate that the crater's basin is nevertheless shallow, suggesting that the subsurface ice was warm and mushy enough to collapse and fill in the deep hole. The first close-ups revealing the rough texture and "swirly" patterns in the material in which the previously photographed chunks of iceberg appear to have floated. The texture suggests a watery slush that rose up from below and froze instantly.
Gaps between plates of ice appear to have spread. They also appear to have been partly filled in with wedged-shaped pieces of darker, newer material -- slushy ice or liquid water -- that welled up, froze and cracked. The researchers compared the resulting pattern of narrow linear ridges and parallel grooves in these wedges to new crust formed at mid-ocean ridges on the Earth's sea floor. The researchers concluded that these activities are recent and ongoing because the surfaces involved show so little cratering from meteorite impacts, compared to an ancient surface. However, according to Michael Carr of the U.S. Geological Survey, the Galileo mission itself has provoked a blossoming dispute about whether the underlying models of impact frequency in the outer solar system are correct. This, he said, has introduced a small but frustrating note of ambiguity into the story told by these "fantastic pictures."
Galileo will make further studies of Europa in coming months, and NASA's Europa Orbiter Mission, to be launched in 2003, will seek to determine the nature and size of any subsurface seas there, said Galileo scientist Michael J. S. Belton, of the National Optical Astronomy Observatory in Tucson.