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Sulfuric acid -- a corrosive chemical found on Earth in car
batteries -- exists on the frozen surface of Jupiter's icy moon
"This demonstrates once again that Europa is a really
bizarre place," said Dr. Robert Carlson of NASA's Jet Propulsion
Laboratory (JPL) in Pasadena, CA. "Sulfuric acid occurs in
nature, but it isn't plentiful. You're not likely to find
sulfuric acid on Earth's beaches, but on Europa, it covers large
portions of the surface."
The new findings from NASA's Galileo spacecraft are reported
in the Oct. 1 issue of the journal Science. Carlson, the
principal investigator for the near-infrared mapping spectrometer
aboard Galileo, is the lead author of the paper.
Although there is no evidence of life on Europa, pictures
and other scientific information gathered by the Galileo
spacecraft indicate a liquid ocean may lie beneath Europa's icy
crust. Water is one key ingredient essential for life.
At first, Carlson thought the spectrometer's findings of
sulfuric acid on Europa would quash any talk that life might
exist there. "After all, even though we know there are acid-
loving bacteria on Earth, sulfuric acid is a nasty chemical," he
said. Those thoughts were quickly negated by a colleague, Dr.
Kenneth Nealson, head of JPL's astrobiology unit, who was excited
by the findings.
"Although sulfur may seem like a harsh chemical, its
presence on Europa doesn't in any way rule out the possibility of
life," Nealson said. "In fact, to make energy, which is
essential to life, you need fuel and something with which to burn
it. Sulfur and sulfuric acid are known oxidants, or energy
sources, for living things on Earth. These new findings
encourage us to hunt for any possible links between the sulfur
oxidants on Europa's surface, and natural fuels produced from
Europa's hot interior."
"These findings have helped solve a puzzle that has been
nagging at me for a long time," Carlson said. "Data gathered by
the spectrometer during observations of Europa had shown a
chemical that we couldn't identify. I kept wondering, 'What the
heck is this stuff?' Lab measurements now tell us that it is
sulfuric acid, and we can start investigating where it comes from
and what other materials might be there." For example, some
reddish-brown areas on Europa might be caused by sulfur that co-
exists with the sulfuric acid.
One theory proposed by Carlson is that the sulfur atoms
originate with the volcanoes on Jupiter's fiery moon Io, with the
material being ejected into the magnetic environment around
Jupiter and eventually whirled toward Europa. Another idea is
that the sulfuric acid comes from Europa's interior, beneath the
moon's icy crust, ejected by sulfuric acid geysers or oozing up
through cracks in the ice.
Another theory comes from Carlson's co-author, Professor
Robert Johnson of the University of Virginia in Charlottesville,
who noted that sodium and magnesium sulfates may have leached
onto Europa's surface from underground oceans and then were
altered by the intense radiation field. This would produce the
frozen sulfuric acid and other sulfur compounds. The new finding
is also consistent with earlier Galileo spectrometer data
analyses reported by Dr. Thomas McCord of the University of
Hawaii and other members of the instrument team, who suggested
that sulfate salts of this type were present on Europa.
Carlson, Johnson and co-author Mark Anderson, a chemist in
JPL's Analytical Chemistry Laboratory, plan to study Jupiter's
largest moon, Ganymede, to see if it also contains sulfuric acid.
The near-infrared mapping spectrometer works like a prism to
break up infrared light not visible to the naked eye. Scientists
can study the resulting light patterns to determine what
chemicals are present, since different chemicals absorb infrared
An image depicting sulfuric acid on Europa is available at:
Galileo has been orbiting Jupiter and its moons for nearly
four years. More information on the Galileo mission is available at:
JPL manages the Galileo mission for NASA's Office of Space
Science, Washington, D.C. JPL is a division of the California
Institute of Technology, Pasadena, CA.