[meteorite-list] Clay-Like Minerals Found on Icy Crust of Europa

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.php?release=2013-362

Clay-Like Minerals Found on Icy Crust of Europa
Jet Propulsion Laboratory
December 11, 2013

A new analysis of data from NASA's Galileo mission has revealed clay-type 
minerals at the surface of Jupiter's icy moon Europa that appear to have 
been delivered by a spectacular collision with an asteroid or comet. This 
is the first time such minerals have been detected on Europa's surface. 
The types of space rocks that deliver such minerals typically also often 
carry organic materials. 

"Organic materials, which are important building blocks for life, are 
often found in comets and primitive asteroids," said Jim Shirley, a research 
scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif. Shirley 
is giving a talk on this topic at the American Geophysical Union meeting 
in San Francisco on Friday, Dec. 13. "Finding the rocky residues of this 
comet crash on Europa's surface may open up a new chapter in the story 
of the search for life on Europa," he said. 

Many scientists believe Europa is the best location in our solar system 
to find existing life. It has a subsurface ocean in contact with rock, 
an icy surface that mixes with the ocean below, salts on the surface that 
create an energy gradient, and a source of heat (the flexing that occurs 
as it gets stretched and squeezed by Jupiter's gravity). Those conditions 
were likely in place shortly after Europa first coalesced in our solar 
system. 

Scientists have also long thought there must be organic materials at Europa, 
too, though they have yet to detect them directly. One theory is that 
organic material could have arrived by comet or asteroid impacts, and 
this new finding supports that idea. 

Shirley and colleagues, funded by a NASA Outer Planets Research grant, 
were able to see the clay-type minerals called phyllosilicates in near-infrared 
images from Galileo taken in 1998. Those images are low resolution by 
today's standards, and Shirley's group is applying a new technique for 
pulling a stronger signal for these materials out of the noisy picture. 
The phyllosilicates appear in a broken ring about 25 miles (40 kilometers) 
wide, which is about 75 miles (120 kilometers) away from the center of 
a 20-mile-diameter (30 kilometers) central crater site. 

The leading explanation for this pattern is the splash back of material 
ejected when a comet or asteroid hits the surface at an angle of 45 degrees 
or more from the vertical direction. A shallow angle would allow some 
of the space rock's original material to fall back to the surface. A more 
head-on collision would likely have vaporized it or driven that space 
rock's materials below the surface. It is hard to see how phyllosilicates 
from Europa's interior could make it to the surface, due to Europa's icy 
crust, which scientists think may be up to 60 miles (100 kilometers) thick 
in some areas. 

Therefore, the best explanation is that the materials came from an asteroid 
or comet. If the body was an asteroid, it was likely about 3,600 feet 
(1,100 meters) in diameter. If the body was a comet, it was likely about 
5,600 feet (1,700 meters) in diameter. It would have been nearly the same 
size as the comet ISON before it passed around the sun a few weeks ago. 

"Understanding Europa's composition is key to deciphering its history 
and its potential habitability," said Bob Pappalardo of JPL, the pre-project 
scientist for a proposed mission to Europa. "It will take a future spacecraft 
mission to Europa to pin down the specifics of its chemistry and the implications 
for this moon hosting life." 

For more information about Europa, visit: 

http://solarsystem.nasa.gov/europa/home.cfm  .

JPL is a division of the California Institute of Technology in Pasadena.

Jia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jccook at jpl.nasa.gov 

2013-362