New Images Hint at Wet and Wild History for Europa

From: Jan Wee <>
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  Wed Apr  9 11:15:14 1997
>Return-Path: <>
>Date: Wed, 9 Apr 1997 14:12:52 -0400 (EDT)
>Subject:  New Images Hint at Wet and Wild History for Europa
>To: undisclosed-recipients.;
>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
>     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 
>     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 
>     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: 
>NOTE TO EDITORS:  Stills and animation of the Galileo spacecraft 
>are available by calling the JPL Public Information Office at 
>                          - end -