STARDUST Presentation

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Science (1999) Vol. 283 p 1135-1138
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Introduction
A Brief Introduction - Max How we know
polycyclic aromatic hydrocarbons are ubiquitous
and abundant in space - Lou Interstellar
conditions and how we simulate them - Scott
How we analyzed the samples (L2MS) - Dick Our
results and their astrobiological significance -
Max Conclusions - Max
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A little context

• Space was considered chemically barren for most
  of the 20th Century
• The spell was broken in the 1960s and 1970s
  with these discoveries
• OH (early 60s)
• NH3 (1968)
• H2CO (1969)
• CO (1970)
• 11.3 µm emission (1973)

polyatomic molecules containing at least 2
atoms other than H can form in the interstellar
medium. Snyder, Buhl, Zuckerman, Palmer
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Center of the Orion Nebula
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EMISSION FROM ORION
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Soot Particles are Mainly PAHS
SOOT PARTICLE
PAH MOLECULE
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Darken room and cover projector lens for
fluorescence demonstration
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UV Pumped Infrared Fluorescence
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PAH EMISSION FROM NEARBY SPIRAL GALAXY MESSIER
81.
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PAH EMISSION FROM THE SOMBRERO GALAXY MESSIER
104.
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What happens to PAHS in Cold, Dark Interstellar
Clouds ???
TOP OF THE HORSEHEAD NEBULA
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Astrochemistry - A middling difficult enterprise
Physicists love the early universe -- because it
is EASY. Youve got protons, electrons, light,
and thats it. Once atoms come together, you get
chemistry, then biology, then economics it
pretty much goes to hell. -Andrew Lange
(5/3/2000)
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How do we simulate chemistry in the interstellar
medium?
Much of the material in galaxies exists in
Dense Molecular Clouds that consist of a
mixture of dust, gas, and ices
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How do we simulate the interstellar medium?
These dense clouds are the site of star
formation
Material from these clouds can find its way
into/onto newly formed planets
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How do we simulate the interstellar medium?
The dust in these dense clouds blocks out
starlight and their interiors can get very cold
(T lt 50 K).
The pressures are very low
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How do we simulate the interstellar medium?
The radiation field can be high (UV and
particle radiation)This radiation clearly
illuminates PAHs associated with the clouds
Visible Light
PAH Emission
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Interstellar Dust ice mantle evolution
Thus, at the low temperatures found in these
clouds, most molecules are expected to freeze out
onto the dust grains where they may be exposed to
ionizing radiation

• Bernstein, Sandford, Allamandola , Sci. Am.
  7,1999, p26

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We can get an idea of what the ices are made of
by measuring the absorption spectra of the cloud
material
The main ice ingredient is always H2O.
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So, to simulate dense cloud conditions we need to
recreate low T, low P, high radiation conditions
with PAHs in H2O-rich ices exposed to radiation
Cryo-vacuum Sample Head
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Lots of plumbing
Cryo-vacuum System (w/o spectrometer)
H2 Lamp On
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Brown Organic Residue Produced by Low Temperature
UV Ice Irradiation
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Analysis of the Samples
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Laser-Desorption Laser-Ionization Mass
Spectrometer
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Two-Step Laser Mass Spectrometry
I. Laser desorption of neutral molecules
II. Laser ionization of selected species
selective ionization of aromatics
pulsed UV laser
plume of neutral molecules
pulsed IR laser
to detector
sample
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Principles ofTime-of-Flight Mass Spectrometry
Kinetic Energy z?V 1/2mv2
Arrival Time t d/v
d/(2z ?V/m)1/2
dm/(2z?V)1/2
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Two-Step Laser Mass Spectrometry
pulsed IR beam
Reflectron
Acceleration grids
time of flight chamber
pulsed UV beam
Mass Deflectors
Einzel lens
MCP detector
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The peaks at 316, 332, and 348 amu correspond to
the addition of one to three O atoms,
respectively, likely in the form of ketones or
hydroxyl side groups (or both).
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The peak at 290 amu corresponds to the addition
of an O atom with loss of two H atoms, consistent
with an ether bridging the molecules bay region.
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Summary
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Astrobiological Implications The Search for Life
and see a whale breaching in the oceans of Europa
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Astrobiological Implications The Search for Life
Alkylated PAHs were invoked as biomarkers in the
Martian meteorite ALH84001 McKay et al., (1996)
Science, Vol. 273, p. 924-930. "Search for past
life on Mars Possible relic biogenic activity in
martian meteorite ALH84001"
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Astrobiological Implications The Search for Life
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Astrobiological Implications The Origin of Life
We see this class of compounds facilitating the
most basic chemical reactions in "primitive"
organisms thus we believe that these molecules
are ancient
Thermoproteus tenax (a "primitive" organism) use
menaquinones as their primary quinone, and in
most Bacteria and Archaea, MK and related
naphthoquinones seem to be very fundamental
ancient are manufactured via Shikimate, couple
important biochemical reactions (i.e. Fumarate to
Succinate), are involved in active transport of
amino acids, and replace or augment ubiquinone or
plastoquinone as electon transport and oxidative
phosphorylation co-enzymes
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Conclusions

• The results explain many molecules seen in
  meteorites.
• These species resemble biomarkers, and thus are
  relevant
• to the search for life.
• They are members of a class of compounds that is
  
• ubiquitous in space.
• Quinones play fundamental roles in life's
  chemistry now and
• probably did so from the beginning.

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Thanks
Advice, edits, and patience of our friends here
at NASA-Ames and Stanford, Technical support from
dedicated lab technicians, Support from our
local management and, Financial support from
NASA's Astrophysics and Planetary Science
Divisions at NASA HQ
Our thanks also to our coauthor colleagues who
were unable to attend this presentation. It
wouldnt have happened without them.
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Prof. Zare receiving H. Julian Allen Award from
Simon P. Worden, Ph.D., BGen. (USAF, Ret.), who
is the Director of the NASA Ames Research Center
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Photo of all presenters Simon P. Worden, Scott
A. Sanford, Richard N. Zare, Max P. Berstein,
and Louis J. Allamandola. Unfortunately, two
other authors could not be present J. Seb
Gillette and Simon J. Clemett. (Photo by Dr.
Jennifer Heldmann)
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