Andrew Yee
March 28th 06, 02:37 PM
Pacific Northwest National Laboratory
Richland, Washington
Contact: Bill Cannon, PNNL
(509) 375-3732
Release date: March 27, 2006
From Europa to the lab, a new recipe for oxygen on icy moons
ATLANTA -- Some may be surprised to learn that bleach-blondes and the
enabler of life elsewhere in our solar system have something in common.
And, no, it's not intelligence. It is, in fact, hydrogen peroxide.
But how that hydrogen peroxide emerges from ice to become life-sustaining
oxygen has been unclear. Now, a new study at the Department of Energy's
Pacific Northwest National Laboratory in Richland, Wash., offers the most
detailed picture to date on how oxygen can be made in frigid reaches far
from Earth.
Since its discovery on Jupiter's Europa and other icy moons orbiting large
gaseous worlds, extraterrestrial ice as a source for oxygen has presented
the tantalizing possibility of complex life around other planets. Yet
planetary scientists have struggled to explain how, in the absence of
sufficient heat, oxygen could be produced from the permafrost surfaces for
use, in Europa's case, by whatever life forms that might inhabit oceans
trapped beneath.
The standard explanation is that abundant high-energy particles from space
-- protons, ultraviolet photons, electrons -- break the molecular bonds
that chain oxygen to hydrogen. (The geophysics -- how the oxygen gets into
the ocean as ice is -- is another story, one involving a
conveyor-belt-like recycling of surface ice into the ocean.)
Those previous oxygen-production models, however, don't jibe with what
staff scientist Greg Kimmel and his colleagues at the PNNL-based W.R.
Wiley Environmental Molecular Sciences Laboratory have been seeing in
experiments, Kimmel reported Monday at the annual meeting of the American
Chemical Society.
"The previous model was a two-step process," Kimmel said. "First, an
energetic particle produces a stable precursor" -- say, two hydrogen atoms
coupled with two oxygen atoms (hydrogen peroxide) or a hydrogen atom
paired with two oxygen atoms. "In step two, another energetic particle
produces O2, or molecular oxygen, from the stable precursor."
Kimmel and colleagues grew a microscopically thin ice film on a platinum
surface, under a vacuum, and bombarded the film with high-energy
electrons.
The bursts lasted 30 to 60 seconds at 30 to 130 degrees Kelvin,
approximating the minus-hundreds-of-degrees-Fahrenheit temperatures on the
icy moons. Afterward, they measured the amount and location, determined by
the oxygen isotopes used to construct layers of the ice film, and
discovered that intermediate species of hydrogen-oxygen permeated the
films.
"We found that a simpler two-step could not account for our results,"
Kimmel said. "Our model is a four-step process." First, the energetic
particle produces what is known as a common "reactive oxygen species"
called a hydroxyl radical, or OH. Next, two OH molecules react to produce
hydrogen peroxide. Third, another OH reacts with the hydrogen peroxide to
form HO2 (hydrogen coupled to two oxygen atoms), plus a water molecule.
And, finally, an energetic particle splits an oxygen molecule from the
HO2.
The experiment introduced another new twist. "One might have expected O2
to be produced throughout the region where the electrons penetrate in the
film," Kimmel noted. "But this is not the case. It appears that the OH's
can be made deeper in the film, but that they subsequently diffuse to and
collect at the ice surface with the rest of the reactions (steps 2-4
above) preferentially occurring there."
PNNL (www.pnl.gov) is a DOE Office of Science laboratory that solves
complex problems in energy, national security, the environment and life
sciences by advancing the understanding of physics, chemistry, biology and
computation. PNNL employs 4,100 staff, has an annual budget of more than
$700 million, and has been managed by Ohio-based Battelle since the lab's
inception in 1965.
Richland, Washington
Contact: Bill Cannon, PNNL
(509) 375-3732
Release date: March 27, 2006
From Europa to the lab, a new recipe for oxygen on icy moons
ATLANTA -- Some may be surprised to learn that bleach-blondes and the
enabler of life elsewhere in our solar system have something in common.
And, no, it's not intelligence. It is, in fact, hydrogen peroxide.
But how that hydrogen peroxide emerges from ice to become life-sustaining
oxygen has been unclear. Now, a new study at the Department of Energy's
Pacific Northwest National Laboratory in Richland, Wash., offers the most
detailed picture to date on how oxygen can be made in frigid reaches far
from Earth.
Since its discovery on Jupiter's Europa and other icy moons orbiting large
gaseous worlds, extraterrestrial ice as a source for oxygen has presented
the tantalizing possibility of complex life around other planets. Yet
planetary scientists have struggled to explain how, in the absence of
sufficient heat, oxygen could be produced from the permafrost surfaces for
use, in Europa's case, by whatever life forms that might inhabit oceans
trapped beneath.
The standard explanation is that abundant high-energy particles from space
-- protons, ultraviolet photons, electrons -- break the molecular bonds
that chain oxygen to hydrogen. (The geophysics -- how the oxygen gets into
the ocean as ice is -- is another story, one involving a
conveyor-belt-like recycling of surface ice into the ocean.)
Those previous oxygen-production models, however, don't jibe with what
staff scientist Greg Kimmel and his colleagues at the PNNL-based W.R.
Wiley Environmental Molecular Sciences Laboratory have been seeing in
experiments, Kimmel reported Monday at the annual meeting of the American
Chemical Society.
"The previous model was a two-step process," Kimmel said. "First, an
energetic particle produces a stable precursor" -- say, two hydrogen atoms
coupled with two oxygen atoms (hydrogen peroxide) or a hydrogen atom
paired with two oxygen atoms. "In step two, another energetic particle
produces O2, or molecular oxygen, from the stable precursor."
Kimmel and colleagues grew a microscopically thin ice film on a platinum
surface, under a vacuum, and bombarded the film with high-energy
electrons.
The bursts lasted 30 to 60 seconds at 30 to 130 degrees Kelvin,
approximating the minus-hundreds-of-degrees-Fahrenheit temperatures on the
icy moons. Afterward, they measured the amount and location, determined by
the oxygen isotopes used to construct layers of the ice film, and
discovered that intermediate species of hydrogen-oxygen permeated the
films.
"We found that a simpler two-step could not account for our results,"
Kimmel said. "Our model is a four-step process." First, the energetic
particle produces what is known as a common "reactive oxygen species"
called a hydroxyl radical, or OH. Next, two OH molecules react to produce
hydrogen peroxide. Third, another OH reacts with the hydrogen peroxide to
form HO2 (hydrogen coupled to two oxygen atoms), plus a water molecule.
And, finally, an energetic particle splits an oxygen molecule from the
HO2.
The experiment introduced another new twist. "One might have expected O2
to be produced throughout the region where the electrons penetrate in the
film," Kimmel noted. "But this is not the case. It appears that the OH's
can be made deeper in the film, but that they subsequently diffuse to and
collect at the ice surface with the rest of the reactions (steps 2-4
above) preferentially occurring there."
PNNL (www.pnl.gov) is a DOE Office of Science laboratory that solves
complex problems in energy, national security, the environment and life
sciences by advancing the understanding of physics, chemistry, biology and
computation. PNNL employs 4,100 staff, has an annual budget of more than
$700 million, and has been managed by Ohio-based Battelle since the lab's
inception in 1965.