Intense ultraviolet radiation that pierces Mars’ thin
atmosphere produces an abundance of oxygen ions, a common free
radical, at the Martian surface that destroys organic molecules –
– the building blocks of life — according to researchers at
NASA’s Jet Propulsion Laboratory, Pasadena, Calif.
Scientists have been puzzled since the mid-1970s when NASA’s
Viking landers failed to find any organic materials, not even
traces delivered to Mars by meteorites. That discovery led
scientists to recognize that there were oxidants in the Martian
soil capable of destroying organic molecules. It has taken until
now for a team to come up with a comprehensive idea of what those
oxidizing chemicals are and how they form.
“We simulated the Martian surface environment in our
laboratory and found that the combination of ultraviolet
radiation, mineral grain surfaces, atmospheric oxygen and
extremely dry conditions produce superoxide ions. This is all
that is necessary to make the reactive component of soil,” said
Dr. Albert Yen, a JPL planetary scientist and lead author of the
study being published in Science magazine on September 15.
This combination of surface conditions exists on Mars today
and the superoxides are generated during daytime exposures to
ultraviolet radiation.
“Our research does not address whether life ever formed on
Mars, but it does give us more information about where to look
for life or evidence of past life,” Yen said. “Evidence of life
might exist beneath the surface or in the interiors of rocks that
are protected from the superoxide ions. What we don’t know is
how far below the surface we would need to look.”
“Determining how deep that oxidizing layer is on Mars is the
most important next step in searching for life there,” said
Caltech Professor Bruce Murray, a co-author on the study.
The research team plans to study the movement of these
oxygen radicals under simulated Martian conditions to estimate
how deep they may be distributed. Future experiments to search
for subsurface organic molecules could be carried out by
penetrators and/or by drilling from a surface lander.
The Martian soil experiment was conducted at JPL for NASA’s
Office of Space Science and the Office of Life and Microgravity
Sciences and Applications, Washington, D.C. JPL is a division of
the California Institute of Technology, Pasadena.
Related Links
° Life on Mars, Whole Mars Catalog
° 15 September 2000: Evidence That the Reactivity of the Martian Soil Is Due to Superoxide Ions, Science, [summary – can be viewed for free once registered. A subscription fee is required for full access.]
“The Viking Landers were unable to detect evidence of
life on Mars but, instead, found a chemically reactive
soil capable of decomposing organic molecules. This
reactivity was attributed to the presence of one or more
as-yet-unidentified inorganic superoxides or peroxides
in the martian soil. Using electron paramagnetic
resonance spectroscopy, we show that superoxide radical
ions (O2-) form directly on Mars-analog mineral surfaces
exposed to ultraviolet radiation under a simulated
martian atmosphere. These oxygen radicals can explain
the reactive nature of the soil and the apparent absence
of organic material at the martian surface. “
