From: Jan Wee <jwee@mail.arc.nasa.gov>
Subject: New Images Hint at Wet and Wild History for Europa
Date: Wed, 09 Apr 1997 13:33:52 -0500
News about Europa for those who are interested in Mars' not too distant neighbors. Jan Wee, moderator ******************************************************************* >>From owner-press-release-nasa@spinoza.hq.nasa.gov Wed Apr 9 11:15:14 1997 >Return-Path: <owner-press-release-nasa@spinoza.hq.nasa.gov> >Date: Wed, 9 Apr 1997 14:12:52 -0400 (EDT) >From: NASANews@hq.nasa.gov >Subject: New Images Hint at Wet and Wild History for Europa >Sender: owner-press-release@spinoza.hq.nasa.gov >To: undisclosed-recipients.;@spinoza.hq.nasa.gov > >Donald Savage >Headquarters, Washington, DC April 9, 1997 >(Phone: 202/358-1547) > >Jane Platt >Jet Propulsion Laboratory, Pasadena, CA > (Phone: 818/354-5011) > >RELEASE: 97-66 > >NEW IMAGES HINT AT WET AND WILD HISTORY FOR EUROPA > > Chunky ice rafts and relatively smooth, crater-free patches >on the surface of Jupiter's frozen moon Europa suggest a younger, >thinner icy surface than previously believed, according to new >images from Galileo's spacecraft released today. > > The images were captured during Galileo's closest flyby of >Europa on Feb. 20, 1997, when the spacecraft came within 363 miles >of the Jovian moon. These features, which lend credence to the >idea of hidden, subsurface oceans, also are stirring up >controversy among scientists who disagree about the age of >Europa's surface. > > Dr. Ronald Greeley, an Arizona State University geologist and >Galileo imaging team member, said 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," Dr. 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." > > The new images of Europa's surface also have sparked a lively >debate among scientists. 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. In essence, Chapman, a planetary scientist at Southwest >Research Institute, Boulder, CO, believes the fewer the craters, >the younger the region. Clark 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." > > Chapman added, "Europa's extraordinary surface geology >indicates an extreme youthfulness -- a very alive world in a state >of flux." > > However, Carr sees things differently. He puts Europa's >surface age at 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." > > Scientists hope to find answers to some of the questions >surrounding Europa and its possible oceans as the Galileo >spacecraft continues its journey through the Jovian system. > > "We want to look for evidence of current activity on Europa, >possibly some erupting geysers," Greeley said. "We also want to >know whether Europa's surface has changed since the Voyager >spacecraft flyby in 1979, or even during the time of the Galileo >flybys." > > The craft will return for another Europa flyby on Nov. 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 also will include encounters with two >other Jovian moons, Callisto and Io. > > The Jet Propulsion Laboratory manages the Galileo mission for >NASA's Office of Space Science, Washington, DC. > > Images and other data received from Galileo are posted on the >Galileo mission home page on the World Wide Web at URL: > > http://www.jpl.nasa.gov/galileo. > >NOTE TO EDITORS: Stills and animation of the Galileo spacecraft >are available by calling the JPL Public Information Office at >818/354-5011. > > - end - > >