science (1999) vol. 283 p 1135-1138

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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…A little context… Space was considered chemically

barren for most of the 20th Century

The spell was broken in the 1960’s and 1970’s with these discoveries:

OH (early 60’s)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 NebulaCenter of the Orion Nebula

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EMISSION FROM ORION

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Soot Particles are Mainly PAHSSoot Particles are Mainly PAHS

SOOT PARTICLEPAH MOLECULE

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Darken room and cover projector lens

for fluorescence demonstration

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UV

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, What happens to PAHS in Cold, Dark Interstellar Clouds ???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. You’ve got protons, electrons, light, and that’s 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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• The dust in these dense clouds blocks out starlight and their interiors can get very cold (T < 50 K).

How do we simulate the interstellar medium?

• 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

18Bernstein, Sandford, Allamandola , Sci. Am. 7,1999, p26 Bernstein, Sandford, Allamandola , Sci. Am. 7,1999, p26

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

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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

pulsed IR laser

sample

AAAB

B

B

plume of neutral

moleculesto detector

pulsed UV laser

selective ionization of

aromatics

BB

BA

AAA+

A+

A+

I. Laser desorption of neutral molecules

II. Laser ionization of selected species

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Principles ofTime-of-Flight Mass Spectrometry

Kinetic Energy = zV = 1/2mv2

Arrival Time = t = d/v = d/[(2z V/m)]1/2

= d[m/(2zV)]1/2

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time of flight chamber

pulsed IR beam

pulsed UV

beam

Reflectron

Mass Deflectors

Einzel lens

Acceleration grids

MCP detector

Two-Step Laser Mass Spectrometry

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QuickTime™ and aMotion JPEG OpenDML decompressor

are needed to see this picture.

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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 molecule’s 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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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"

Astrobiological Implications: The Search for Life

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OH OH

O

O

R

Aloe-Emodin

Arch. Pharm. 247, 81 (1909)

Rhein (extract of chinese rhubarb)

Ann. 50, 196 (1844)

O

O

OH

Juglone (in walnut & pecan shells)

Bull. Soc. Chim . 1, 800 (1907)

Astrobiological Implications: The Search for Life

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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

S8

H2 +

R-H or H2S

R

R'O

O

T. tenax

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

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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 wouldn’t 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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