[meteorite-list] NASA Research Reveals Europa's Mystery Dark Material Could Be Sea Salt

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.php?feature=4586

NASA Research Reveals Europa's Mystery Dark Material Could Be Sea Salt
Jet Propulsion Laboratory
May 12, 2015

The puzzling, fascinating surface of Jupiter's icy moon Europa looms large 
in this reprocessed color view, made from images taken by NASA's Galileo 
spacecraft in the late 1990s. Image credit: NASA/JPL-Caltech/SETI Institute
NASA laboratory experiments suggest the dark material coating some geological 
features of Jupiter's moon Europa is likely sea salt from a subsurface 
ocean, discolored by exposure to radiation. The presence of sea salt on 
Europa's surface suggests the ocean is interacting with its rocky seafloor 
-- an important consideration in determining whether the icy moon could 
support life.

The study is accepted for publication in the journal Geophysical Research 
Letters and is available online.

"We have many questions about Europa, the most important and most difficult 
to answer being is there life? Research like this is important because 
it focuses on questions we can definitively answer, like whether or not 
Europa is inhabitable," said Curt Niebur, Outer Planets Program scientist 
at NASA Headquarters in Washington. "Once we have those answers, we can 
tackle the bigger question about life in the ocean beneath Europa's ice 
shell."

For more than a decade, scientists have wondered about the nature of the 
dark material that coats long, linear fractures and other relatively young 
geological features on Europa's surface. Its association with young terrains 
suggests the material has erupted from within Europa, but with limited 
data available, the material's chemical composition has remained elusive.

"If it's just salt from the ocean below, that would be a simple and elegant 
solution for what the dark, mysterious material is," said research lead 
Kevin Hand, a planetary scientist at NASA's Jet Propulsion Laboratory 
in Pasadena, California.

One certainty is that Europa is bathed in radiation created by Jupiter's 
powerful magnetic field. Electrons and ions slam into the moon's surface 
with the intensity of a particle accelerator. Theories proposed to explain 
the nature of the dark material include this radiation as a likely part 
of the process that creates it.

Previous studies using data from NASA's Galileo spacecraft, and various 
telescopes, attributed the discolorations on Europa's surface to compounds 
containing sulfur and magnesium. While radiation-processed sulfur accounts 
for some of the colors on Europa, the new experiments reveal that irradiated 
salts could explain the color within the youngest regions of the moon's 
surface.

To identify the dark material, Hand and his co-author Robert Carlson, 
also at JPL, created a simulated patch of Europa's surface in a laboratory 
test apparatus for testing possible candidate substances. For each material, 
they collected spectra -- which are like chemical fingerprints -- encoded 
in the light reflected by the compounds.

"We call it our 'Europa in a can,'" Hand said. "The lab setup mimics conditions 
on Europa's surface in terms of temperature, pressure and radiation exposure. 
The spectra of these materials can then be compared to those collected 
by spacecraft and telescopes."

For this particular research, the scientists tested samples of common 
salt -- sodium chloride -- along with mixtures of salt and water, in their 
vacuum chamber at Europa's chilly surface temperature of minus 280 degrees 
Fahrenheit (minus 173 Celsius). They then bombarded the salty samples 
with an electron beam to simulate the intense radiation on the moon's 
surface.

After a few tens of hours of exposure to this harsh environment, which 
corresponds to as long as a century on Europa, the salt samples, which 
were initially white just like table salt, turned a yellowish-brown color 
similar to features on the icy moon. The researchers found the color of 
these samples, as measured in their spectra, showed a strong resemblance 
to the color within fractures on Europa that were imaged by NASA's Galileo 
mission.

"This work tells us the chemical signature of radiation-baked sodium chloride 
is a compelling match to spacecraft data for Europa's mystery material," 
Hand said.

Additionally, the longer the samples were exposed to radiation, the darker 
the resulting color. Hand thinks scientists could use this type of color 
variation to help determine the ages of geologic features and material 
ejected from any plumes that might exist on Europa.

Previous telescope observations have shown tantalizing hints of the spectral 
features seen by the researchers in their irradiated salts. But no telescope 
on or near Earth can observe Europa with sufficiently high resolving power 
to identify the features with certainty. The researchers suggest this 
could be accomplished by future observations with a spacecraft visiting 
Europa.

JPL built and managed NASA's Galileo mission for the agency's Science 
Mission Directorate in Washington, and is developing a concept for a future 
mission to Europa. The California Institute of Technology in Pasadena 
manages JPL for NASA.

For more information about Europa, visit:

http://europa.jpl.nasa.gov


Media Contact

Preston Dyches
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-7013
preston.dyches at jpl.nasa.gov 

Dwayne Brown
NASA Headquarters, Washington
202-358-1726
dwayne.c.brown at nasa.gov 

2015-166