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EUROPA: WETÝANDÝWILD
By Sean Henahan, Access Excellence PASADENA (4/9/97) Stunning new photos transmitted by the Galileo spacecraft have revealed what may be a huge ocean of water, leading some scientists to predict that finding life there is all but inevitable.  Caption:
Depicts an area 32 km x 40 km. Area includes ridges 6 km across.
Some ridges reach heights of about 180 m. Other features include a hill
in the center of the picture about 480 m high. Two mounds about 6 km across
are seen in the bottom of the picture. The ridges, hills and mounds probably
all represent uplifts of the icy crust of Europa by processes originating
from the interior.
The images were captured on February 20, when the spacecraft came within 586 kilometers (363 miles) of Europa. The photos show chunky ice rafts and relatively smooth, crater-free patches, suggesting a younger, thinner icy surface than previously believed. According to Dr. Ronald Greeley, an Arizona State University geologist and Galileo imaging team member, the ice rafts reveal that Europa had, and may still have, a very thin ice crust covering either liquid water or slush. "We're intrigued by these blocks of ice, similar to those seen on Earth's polar seas during springtime thaws," Greeley said. "The size and geometry of these features lead us to believe there was a thin icy layer covering water or slushy ice, and that some motion caused these crustal plates to break up." "These rafts appear to be floating and may, in fact, be comparable to icebergs here on Earth," said another Galileo imaging team member, Dr. Michael Carr, a geologist with the U.S. Geological Survey. "The puzzle is what causes the rafts to rotate. The implication is that they are being churned by convection." Scientists believe the same components and conditions that originally may have produced life on Earth may be present on Europa. Indeed, the presence of water, the effects of volcanic warming and the right mix of chemicals may have already produced life there, noted some researchers at a press conference. "I am sure there's life there,'' said John Delaney of the University of Washington, citing previous research indicating that volcanic activity can supports life without sunlight on Earth. "The bottom line is, it's about life. The discovery of life on another planet will surpass anything that has ever taken place in human history,'' he said. Richard Terrile, a planetary scientist at JPL , noting the likelihood of organic matter in sediment at the bottom of Europa's ocean, said "On Earth, these same ingredients in a million years gave presence to life.'' However, Terrile cautioned: "The water's probably bouillon, but we don't know if it's chicken soup.'' The new images have also warmed the debate on the age of Europa. Galileo imaging team member Dr. Clark Chapman is among those who believe the smoother regions with few craters indicate Europa's surface is much younger than previously believed. He believes the fewer the craters, the younger the region. Chapman based his estimate on current knowledge about cratering rates, or the rate at which astronomical bodies are bombarded and scarred by hits from comets and asteroids. "We're probably seeing areas a few million years old or less, which is about as young as we can measure on any planetary surface besides Earth," said Chapman. "Although we can't pinpoint exactly how many impacts occurred in a given period of time, these areas of Europa have so few craters that we have to think of its surface as young. Europa's extraordinary surface geology indicates an extreme youthfulness -- a very alive world in a state of flux." Dr. Carr, in contrast, believes Europa's surface age may be closer to one billion years old. "There are just too many unknowns," Carr said. "Europa's relatively smooth regions are most likely caused by a different cratering rate for Jupiter and Earth. For example, we believe that both Earth's moon and the Jovian moon, Ganymede, have huge craters that are 3.8 billion years old. But when we compare the number of smaller craters superimposed on these large ones, Ganymede has far fewer than Earth's moon. This means the cratering rate at Jupiter is less than the cratering rate in the Earth-moon system." Galileo will return for another Europa flyby on November 6, 1997, the final encounter of Galileo's primary mission. However, eight more Europa flybys are planned as part of Galileo's two-year extended mission, which will also include encounters with two other Jovian moons, Callisto and Io. Related information on the Internet AEÝReport: Life on Mars
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