Scientists today described how the interaction of hard radiation and ices
in space leads to the production of complex organic molecules. The report
is being presented to the American Astronomical Society meeting in Pasadena,
CA by Drs. Louis Allamandola, Max Bernstein, Jason Dworkin, and Scott
Sandford of the Astrophysics Branch of NASA’s Ames Research Center, in
Moffett Field, CA, Dr. David Deamer of the Biochemistry Department of the
University of California, in Santa Cruz, CA, and Dr. Richard Zare and Ms.
Jamie Elsila of the Department of Chemistry at Stanford University, in
Stanford, CA. The production of organic compounds in space is of special
interest to scientists since these molecules may have played a role in the
origin of life on Earth.

These scientists have been studying the chemistry of organic carbon
compounds that occurs in dense molecular clouds in interstellar space,
the locations where new stars and planetary systems are born. Such clouds
consist of concentrations of dust, ice, and gas that screen out much of
the light produced by outside stars. As a result, the interiors of these
clouds can become very cold, sometimes attaining temperatures as low as
10 Kelvin (-263 C). At these temperatures, many of the molecules and atoms
that are normally present as gases condense to form ice mantles surrounding
the dust particles in the cloud, much as your breath condenses into frost
on a cold window. These ices are primarily made up of simple molecules like
water (H2O), methanol (CH3OH), carbon dioxide (CO2), carbon monoxide (CO),
ammonia (NH3), and methane (CH4).

At such low temperatures, these molecules would not normally be expected to
react with each other, particularly when they are embedded in ice. However,
the ice mantles are exposed to low levels of ionizing radiation in the form
of cosmic rays and ultraviolet photons. This radiation can break apart the
molecules in the ice and produce highly reactive ions and radicals that
can recombine to form larger, more complex molecules.

At NASA-Ames, Allamandola, Sandford, Bernstein, and Dworkin use
cryogenically cooled vacuum chambers and UV lamps in their laboratory to
form and irradiate interstellar ice analogs under conditions that simulate
those found in dense interstellar clouds. “Basically, we freeze mixed
gases onto an extremely cold window and then give the ices the equivalent
of a good suntanning,” says Allamandola. “After the sample is warmed up,
we can remove any remaining organic materials from the sample chamber and
study them using a variety of analytical techniques,” he continued.

One of these is the technique of two step laser-desorption laser-ionization
mass spectrometry. “That’s quite a mouthful,” says Stanford graduate
student Elsila, “but essentially this is an analytical technique that
allows us to measure the masses of the various compounds in the organic
residue that results from the ice irradiation.” “The surprise,” says Zare,
leader of the Stanford group, “is just how complex the population of
organics is. Generally we see a peak at virtually every mass up to and
beyond 500 atomic mass units!” This means that the residue must contain
hundreds of distinctly different molecules, the vast majority of them
being considerably larger than the molecules that made up the original ice.

“We are only just beginning to identify all the compounds that are present,”
notes Dworkin. “One of the more interesting classes of compound we have
identified in the residues are amphiphiles. These molecules have the
interesting property that, if you add them to water, they can spontaneously
form vesicles, that is, walled structures reminiscent of cells.” This
raises the possibility similar materials could have fallen on the early
Earth and played a role in the formation of the first cellular structures.
“There is some precedence for this idea,” notes Deamer, a biochemist from
UCSC and an expert on membranes. “Primitive meteorites are also known to
contain amphiphiles that, when added to water, make structures that are
very similar to those we make from the simulated interstellar residues,”
he continued.

Other chemical compounds the team has been studying is a class of molecules
called “polycyclic aromatic hydrocarbons,” or PAHs for short. These
molecules consist of small sheets of carbon atoms arranged in hexagons with
hydrogen atoms around their edges, much like the shapes you would get if
you cut out pieces of a chicken wire fence. PAHs are common molecules on
the Earth and are a major component of auto exhaust and soot. PAHs are also
very abundant in space, where they are thought to originate primarily in
the outflows of gas given off by stars like our own Sun when they reach the
end of their normal lives. Like the other molecules in space, PAHs should
be frozen into the ice mantles that surround dust grains in interstellar

When the team examined the chemistry that occurred when PAH-containing H2O
ices were irradiated with ultraviolet light, they discovered that the PAHs
were not destroyed, but that many of them did have their edges modified by
the addition of extra oxygen and hydrogen atoms. The addition of oxygen
atoms results in the formation of aromatic alcohols and ketones, i.e., PAHs
where a peripheral H atom is replaced by an -OH group or a doubly bonded
oxygen, respectively. The aromatic ketones are of particular interest.
This class of compounds includes quinones, molecules that currently play
critical metabolic roles in the biochemistry of all living organisms on
Earth. “As with the amphiphiles, this raises the interesting possibility
that the infall of materials made in the interstellar medium may have
played a significant role in getting life started on Earth,” notes
Bernstein, who along with Dworkin, makes most of the residues.

“However,” Allamandola added, “the production of organics in space can’t
play a role in the origin of life on planets if the material is unable to
safely survive transportation from the interstellar medium to the surface
of a newly formed planet. Fortunately, meteorites provide us with evidence
that organic materials can survive this transition.” This evidence comes
primarily from the detection of deuterium enrichments in many meteoritic

Deuterium is one of the heavier isotopes of hydrogen, having one extra
neutron. “It turns out that most of the chemical processes that we think
occur in the interstellar medium favor the heavier deuterium over normal
hydrogen,” says Sandford. “As a result, the presence of excess deuterium
in meteoritic organics strongly suggests an interstellar connection. One
of our current research activities is to try to understand how deuterium
behaves during our ice chemistry simulations. We are discovering patterns
to the placement of deuterium in the resulting organics and one of our
plans for the future is to compare our results to meteoritic organics to
see if the same patterns appear in them.”

Perhaps the most important point of all this, notes Sandford, is that this
type of chemical activity is a universal process that should be happening
in all interstellar dense clouds. “It appears that the universe is, in
some sense, ‘hardwired’ to produce relatively complex organics,” he quips.
“Furthermore, since it is from these clouds that new planetary systems
are made, it is reasonable to expect that essentially all new planets
should have some of this material fall on them. Thus, interstellar
organics may play a wider role in the formation of life on other planets,
not just the Earth.”

This work was funded by the National Aeronautics and Space Administration.

More information:

* The Astrochemistry Lab at NASA Ames

* The equipment used to simulate space (center image)

* Related material in the July 1999 issue of Scientific American

Related material which has appeared in the scientific literature:

* Bernstein, M. P., Sandford, S. A., Allamandola, L. J., Gillette, J. S.,
Clemett, S. J., & Zare, R. N. (1999). UV Irradiation of Polycyclic
Aromatic Hydrocarbons in Ices: Production of Alcohols, Quinones, and
Ethers. Science 283, 1135-1138.

* Bernstein, M. P., Dworkin, J. P., Sandford, S. A., & Allamandola, L. J.
(2001). Ultraviolet Irradiation of Naphthalene in H2O Ice: Implications
for Meteorites and Biogenesis. Meteoritics and Planetary Science, 36,

* Dworkin, J. P., Deamer, D. W., Sandford, S. A., & Allamandola, L. J.
(2001). Self-Assembling Amphiphilic Molecules: Synthesis in Simulated
Interstellar/Precometary Ices. Proc. Nat. Acad. Sci. 98, 815-819.

Images of vesicle research:

[Image 1: (286KB)]
These droplets (~10 microns across) show structures reminiscent of cells
(although they are not alive). They are from a chemically separated
fraction of the bulk residue.

[Image 2: (167KB)]
These droplets (small ones are ~10 microns across) glowing under black
light in the microscope show internal structure and suggest chemical
complexity. They are from a chemically separated fraction of the bulk

[Image 3: (85KB)]
This is a vesicle (~10 microns across) glowing under black light in the
microscope made from the bulk residue. Proof that it is a hollow vesicle,
rather than a simple drop of oil, is the green pyranine dye which we have
trapped inside of it.

Astrochemistry Laboratory

Ames Research Center

Moffett Field, CA

Contact information:

Dr. Louis J. Allamandola

NASA-Ames Research Center


Dr. Max P. Bernstein

Astrophysics Branch, NASA-Ames Research Center


Dr. David Deamer

Dept. of Chemistry and Biochemistry, UC Santa Cruz

831-459-5158, deamer@hydrogen.UCSC.EDU

Dr. Jason P. Dworkin

Astrophysics Branch, NASA-Ames Research Center


Ms. Jamie Elsila

Dept. of Chemistry, Stanford University

650-723-4318, jelsila@Stanford.EDU

Dr. Scott A. Sandford

Astrophysics Branch, NASA-Ames Research Center


Dr. Richard N. Zare

Dept. of Chemistry, Stanford University