Astrochemistry E-Book

Andrew M. Shaw

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 762

Veröffentlichungsjahr: 2021

Beschreibung

A fully revised new edition of an introductory text to the dynamic and fascinating subject of astrochemistry

Since the first edition in 2006 of Astrochemistry, the Mars rovers have driven 31.18 miles, there has been fly-by of Pluto changing it from a 4-pixel world on the Hubble Space Telescope into a mysterious non-planet. There have been visits to asteroids, revisiting Mercury, discovery of the Higgs Boson, discovery of over 2000 extrasolar planets and landing on the comet 67P/Churyumov–Gerasimenko by Rosetta mission – hence the timely publication of this new edition.

This core textbook now includes more detailed information on the kinetic modelling of chemistry in the interstellar medium, extending the same principles of physical chemistry to meteor ablation and finally atmospheres and oceans. The increase in density from near-emptiness to 1.35 x 1021 L of water in the world's oceans is used to take single collision kinetics into ensemble thermodynamics. A new introduction of thermodynamic using meteor ablation replaces traditional bomb calorimetry and per-biotic chemistry leads to spontaneous reactions.

New to the second edition:

• An extended discussion on matter, dark or otherwise, interstellar and stellar chemistry and the origin of pre-biotic molecules
• Detailed chemical kinetic models for mechanisms of chemistry in the interstellar medium
• Origins of life in solution, enzyme kinetics and catalysis
• A review of Mars and Titan as habitats for life
• Fully referenced throughout to reflect the research frontier
• An introduction to the idea of analytical mathematical engines that can do all of the heavy mathematics and fostering the skill of setting up a model and testing it
• 200 problems with detailed solutions

Written for undergraduate and postgraduate students in astrochemistry or more generally physical chemistry, the new edition of Astrochemistry is an important introductory text to the topic, the latest developments in the field and the ubiquity of physical chemistry.

Leseprobe

Table of Contents

Cover

Dedication

Title Page

Copyright

Preface to the First Edition

Units and Conventions

Course Material

Acknowledgements

Preface to the Second Edition

Acknowledgements

About the Companion Website

1 The Molecular Universe

1.1 The Standard Model – Big Bang Theory

1.2 Galaxies, Stars, and Planets

1.3 Origins of Life

1.4 Other Intelligent Life

1.5 Theories of the Origin of Life

1.6 The Search for Extraterrestrial Intelligence (SETI)

Problems

References

2 Starlight, Galaxies, and Clusters

2.1 Simple Stellar Models – Black-Body Radiation

2.2 Cosmic Microwave Background Radiation: 2.725 K

2.3 Stellar Classification

2.4 Constellations

2.5 Galaxies

2.6 Cosmology

Problems

References

3 Atomic and Molecular Astronomy

3.1 Spectroscopy and the Structure of Matter

3.2 Line Shape

3.3 Telescopes

3.4 Atomic Spectroscopy

3.5 Molecular Astronomy

3.6 Molecular Masers

3.7 Detection of Hydrogen

3.8 Diffuse Interstellar Bands

3.9 Spectral Mapping

Problems

References

4 Stellar Chemistry

4.1 Classes of Stars

4.2 Herzprung–Russell Diagram

4.3 Stellar Evolution

4.4 Stellar Spectra

4.5 Exotic Stars

4.6 Cycle of Star Formation

Problems

References

5 The Interstellar Medium

5.1 Mapping Clouds of Molecules

5.2 Molecules in the Interstellar and Circumstellar Medium

5.3 Physical Conditions in the Interstellar Medium

5.4 Rates of Chemical Reactions

5.5 Chemical Reactions in the Interstellar Medium

5.6 Photochemistry

5.7 Charged Particle Chemistry

5.8 Polycyclic Aromatic Hydrocarbons

5.9 Dust Grains

5.10 Chemical Models of Molecular Clouds

5.11 Running the Models

5.12 Prebiotic Molecules in the Interstellar Medium

Problems

References

6 Meteorite and Comet Chemistry

6.1 Phases of Matter, Heat, and Change

6.2 Meteor Ablation

6.3 Enthalpy of Reaction

6.4 Formation of the Solar System

6.5 Classification of Meteorites

6.6 Geological Time

6.7 Chemical Analysis of Meteorites by

μ

L

2

MS

6.8 Comet Chemistry

6.9 Chemical Composition of Comets

6.10 Cometary Collisions with Planets

6.11 The Rosetta Mission

Problems

References

7 Planetary Chemistry

7.1 Structure of a Star–Planet System

7.2 Surface Gravity

7.3 Formation of the Earth

7.4 Earth–Moon System

7.5 Geological Periods

7.6 Radiative Heating

7.7 The Habitable Zone

7.8 Detecting Extrasolar Planets

7.9 Extrasolar Planets – The Current Inventory

7.10 Planetary Atmospheres

7.11 Atmospheric Photochemistry

7.12 Biomarkers in the Atmosphere

Problems

References

8 Prebiotic Chemistry

8.1 Carbon- and Water-Based Life Forms

8.2 Solvent Properties

8.3 Spontaneous Chemical Reactions

8.4 Acid–Base Buffers

8.5 Prebiotic Molecular Inventory

8.6 Exogenous Delivery of Organic Molecules

8.7 Homochirality

8.8 Surface Metabolism

8.9 Geothermal Vents

8.10 RNA World Hypothesis

Problems

References

9 Primitive Life Forms

9.1 Self-Assembly and Encapsulation

9.2 Protocells

9.3 Enzyme Catalysis

9.4 Universal Tree of Life

9.5 Astrobiology

9.6 Subsurface Antarctic Lakes – Astrobiological Time Capsules

Problems

References

10 Mars and Titan – Habitats for Life?

10.1 Solar System Habitats

10.2 Biosignatures

10.3 Contamination

10.4 Mars

10.5 Titan

10.6 Physical-Chemical Properties and the Radiation Budget

10.7 Temperature-Dependent Chemistry

10.8 The Atmospheres

10.9 Astrobiology on Mars and Titan

10.10 And Finally

Problems

References

Appendix A: Constants and Units

Appendix B: Astronomical Data

Appendix C: Thermodynamic Properties of Selected Compounds

Solutions to Problems

Index

End User License Agreement

List of Tables

Chapter 1

Table 1.1 The history of the Universe according to the Standard Model

Table 1.2 Relative cosmic abundance of the elements

Chapter 2

Table 2.1 Magnitude of some heavenly objects (see also Appendix B)

Table 2.2 Physical properties of the Milky Way

Chapter 3

Table 3.1 Atmospheric windows for astronomy

Table 3.2 Comparison of telescope spectral resolution

Table 3.3 The named transition series in the atomic spectrum of hydrogen

Chapter 4

Table 4.1 Stellar classification

Table 4.2 Properties of Sirus B

Table 4.3 Stages of thermonuclear generation in stars

Table 4.4 Stellar evolution

Table 4.5 Nucleosynthesis processes

Table 4.6 Term symbols with their degeneracy for electronic configurations ...

Chapter 5

Table 5.1 Types of molecular clouds and their physical-chemical conditions....

Table 5.2 Molecules detected in the interstellar and circumstellar medium (...

Table 5.3 Bond energies and photodissociation wavelengths

Table 5.4 Ionisation energies and wavelengths

Table 5.5 Molecular abundance relative to H

2

9observed in TMC-1 and L134N. ...

Table 5.6 Initial abundance of the elements relative to H. Source: Agúndez ...

Chapter 6

Table 6.1 Specific heat capacities of some common materials

Table 6.2 Details of the current position of comet Temple-Tuttle (Autumn 20...

Table 6.3 Terms in the meteor ablation equation

Table 6.4 Initial composition of a metal oxide meteor for ablation. Source:...

Table 6.5 Properties of the Sun, currently

Table 6.6 Meteorite falls by class. Source: Hughes 10

Table 6.7 Meteorite mineralogy. Source: Center for Meteorite Studies, Arizo...

Table 6.8 Isotopes and daughter products used in dating

Table 6.9 Soluble organic compounds in the Murchison meteorite. Source: Piz...

Table 6.10 Molecular inventory for Hale-Bopp, observed at

r

h

≈ 1 AU. Source:...

Table 6.11 Properties of comet 67P/Churymuov-Gerasimenko, derived from the ...

Table 6.12 Rosetta mission instrument payload

Table 6.13 Masses uses to deconvolve the mass spectra observed in Figure 6....

Chapter 7

Table 7.1 Planetary data (based on the Earths mass of 5.974 × 10

24

kg and diame...

Table 7.2 Planetary information on surface temperature. Source: Modified from N...

Table 7.3 Atmospheres of the inner planets

Table 7.4 Photolysis mechanism for ozone formation

Chapter 8

Table 8.1 Melting and boiling points of possible solvents for life

Table 8.2 The extent of the CO + H

2

reaction

Table 8.3 Henry's law coefficients for gases dissolved in water and benzene

Table 8.4 Spectrum of pK

a

values and some amino acids

Table 8.5 Typical yield of a Miller–Urey experiment

Chapter 9

Table 9.1 Identified roles of genes in the minimal gene set

Table 9.2 Properties of an ideal minimal cell

Table 9.3 Possible life environments

Table 9.4 Autotrophic reactions and reaction enthalpy

Chapter 10

Table 10.1 Physical and chemical properties of Earth, Mars, and Titan. Sour...

Table 10.2 Photochemical loss mechanisms from the Martian atmosphere. Sourc...

Appendix A

Table A.1 Constants.

Table A.2 Units used in addition to standard SI units.

Table A.3 The SI prefixes.

Table A.4 Conversion factors.

List of Illustrations

Chapter 1

Figure 1.1 The cosmic timeline as it is observed today by the Wilkinson Micr...

Figure 1.2 The proportions of each component of the Universe. Exact proporti...

Figure 1.3 Two species of candle flame – dead or alive? The flame on the lef...

Figure 1.4 Watson–Crick DNA base pairs, and the DNA backbone used by every l...

Figure 1.5 The genetic code. Source: Reproduced from

Alzheimer's Disease Edu

...

Figure 1.6 Hyperthermophile bacteria at Prismatic Lake in Yellowstone Nation...

Figure 1.7 Theories of the origins of life. Source: Reproduced from Davis an...

Figure 1.8 Impact frustration: (a) the Chicxulub crater, seen as a three-dim...

Chapter 2

Figure 2.1 Variation of area, A, increases as the square of the distance, d,...

Figure 2.2 Planck curves for black bodies of different temperatures.

Figure 2.3 Absorption spectrum of chlorophyll overlaid with the energy flux ...

Figure 2.4 An almost-perfect black-body spectrum for the cosmic background r...

Figure 2.5 The cosmic microwave background, Wilkinson Microwave Anisotropy P...

Figure 2.6 The constellation of Orion. This is a mosaic picture of 18 (6 × 3...

Figure 2.7 An apparent-magnitude line that shows what can be seen from Earth...

Figure 2.8 The B-V colour index derived from the theoretical black-body curv...

Figure 2.9 Parallax for nearby stars.

Figure 2.10 The celestial co-ordinates.

Figure 2.11 Signs of the Zodiac.

Figure 2.12 Constellation map for

Ursa Major

.

Figure 2.13 The Great Bear.

Figure 2.14

Ursa Major

viewed side-on.

Figure 2.15 Andromeda Galaxy – just visible with the naked eye on a clear ni...

Figure 2.16 The Milky Way.

Figure 2.17 Very Large Array radio image of Sgr A

8

, which may be a supermass...

Figure 2.18 First image of a black hole recorded by the Event Horizon Telesc...

Figure 2.19 The Local Group of galaxies.

Figure 2.20 Gravitational lensing of blue light from galaxies behind the ora...

Chapter 3

Figure 3.1 Absorption of radiation.

Figure 3.2 The reflection spectrum of Jupiter.

Figure 3.3 Atmospheric windows and molecular astronomy.

Figure 3.4 The Rayleigh criterion.

Figure 3.5 The Pillars of Creation in the Eagle Nebula in the visible, showi...

Figure 3.6 Fomalhaut's circumstellar dust ring, which makes it an extrasolar...

Figure 3.7 Jupiter's Great Red Spot.

Figure 3.8 Spectral evolution of the core of the GRS over time from Hubble S...

Figure 3.9 The hydrogen atom absorption spectrum and named sequences.

Figure 3.10 This exceptional image of the Horsehead nebula was taken at the ...

Figure 3.11 NGC 7252 or O[III] nebula, now famous for the strong O[III] oxyg...

Figure 3.12 The emission spectrum of NGC 7252 in the visible, showing the em...

Figure 3.13 The energy-level diagram for a rotational spectrum.

Figure 3.14 Simulated spectrum of CO with a rotational temperature of 40 K....

Figure 3.15 Rotation axes for the water molecule.

Figure 3.16 Simulated spectrum of CH

3

OH at 40 K.

Figure 3.17 Simulated rotational spectrum of glycine at 40 K.

Figure 3.18 The microwave spectrum of the Orion nebula.

Figure 3.19 Line of sight through three giant molecular clouds to the Hubble...

Figure 3.20 UK Infrared Telescope situated close to the summit of Mauna Kea,...

Figure 3.21 Infrared atmospheric absorption on Mauna Kea.

Figure 3.22 Infrared stretching frequencies.

Figure 3.23 Energy level diagram for the CO ro-vibrational spectrum.

Figure 3.24 (a) Population excitation; (b) population inversion – maser tran...

Figure 3.25 The 21 cm line in the H atom.

Figure 3.26 Diffuse interstellar bands.

Figure 3.27 Multiwavelength view of the Milky Way. From the top: 0.4 GHz rad...

Chapter 4

Figure 4.1 A protostar.

Figure 4.2 Spectra from different stellar classes: OBAFGKM.

Figure 4.3 Herzprung–Russell diagram.

Figure 4.4 Mass birth lines for stars descending onto the main sequence, whe...

Figure 4.5

T-Tauri

Young Stellar Object with characteristic bipolar je...

Figure 4.6 Binding energy of atomic nuclei as a function of atomic number.

Figure 4.7 The triple-alpha process.

Figure 4.8 Cool Ghost Nebula NGC6369. Produced with the FITS Liberator and d...

Figure 4.9 The CNO cycle T > 1.6 × 10

7

K M > 1.1 solar masses.

Figure 4.10 Supernova 1987A, captured by the HST Wide Field Planetary Camera...

Figure 4.11 The current elemental composition of the Sun.

Figure 4.12 The

p

-orbital shapes.

Figure 4.13 The

d

-orbital shapes.

Figure 4.14 The origin of the Zeeman splitting in the

n

 = 2 →

n

=3 transitio...

Figure 4.15 Doppler effect for a binary star pair.

Figure 4.16 Light curve for the star

SX Persei

.

Figure 4.17 The cycle of star formation.

Chapter 5

Figure 5.1 A longitudinal velocity map of

12

CO emission of the entire Milky ...

Figure 5.2 A longitudinal velocity map of

13

CO emission integrated over a 4

O

Figure 5.3 The Orion molecular cloud.

Figure 5.4 The Horsehead nebula just below the belt of Orion, showing beauti...

Figure 5.5 Taurus molecular cloud observed at 115 GHz

12

CO emission.

Figure 5.6 Taurus molecular cloud observed at 120 GHz

13

CO emission.

Figure 5.7 Structure of a giant molecular cloud.

Figure 5.8 Alkanes, alkenes, aromatics, and cyanopolyynes: 1, methane; 2, et...

Figure 5.9 Alcohols, aldehydes, ketones, and acids: 15, ethylene glycol; 16,...

Figure 5.10 Cross-section of the circumstellar region, as a function of dist...

Figure 5.11 Visible extinction and the reddening of stars.

Figure 5.12 Definition of activation energy with and without a catalyst.

Figure 5.13 Reactions in the interstellar medium.

Figure 5.14 Electron–ion and electron–molecule reactions.

Figure 5.15 Hydrocarbon reactions leading to PAH synthesis.

Figure 5.16 Polyaromatic hydrocarbon species: (1) phenanthrene, (2) anthrace...

Figure 5.17 Acetylene polymerisation I.

Figure 5.18 Acetylene polymerisation II.

Figure 5.19 IR spectrum of the compact planetary nebula.

Figure 5.20 W33A Dust-embedded massive young star.

Figure 5.21 Structure of dust particles.

Figure 5.22 Surface reactions.

Figure 5.23 Formation of amino acids on ice surfaces irradiated in the labor...

Figure 5.24 Simple molecule network for the beginning of TMC modelling.

Figure 5.25 Initial reactions in dense molecular clouds.

Figure 5.26 Organic synthesis in hot molecular cores.

Figure 5.27 Abundance of oxygen-bearing molecules as a function of time, as ...

Figure 5.28 Same as Figure 5.27, but for hydrocarbons. For

c

-C

3

H and

l

-C

3

H, ...

Figure 5.29 Same as Figure 5.27, but for nitrogen-bearing molecules.

Figure 5.30 Isomeric structure of glycine.

Figure 5.31 Glycine spectra (at 1 MHZ resolution) observed at 206 468 MHZ (l...

Figure 5.32 A CHON seed.

Chapter 6

Figure 6.1 A Hess cycle for the melting, boiling, and sublimation of water....

Figure 6.2 The phase diagram for water, indicating where we are on Earth, sh...

Figure 6.3 Current position of comet Temple-Tuttle in its orbit. This comet ...

Figure 6.4 Leonid meteor shower. A composite of images taken by the Midcours...

Figure 6.5 Spectra of two fireballs observed in the Czech Republic in 2000 a...

Figure 6.6 Ablation profiles of individual elements from a 5 μg meteoroid en...

Figure 6.7 Na LIDAR measurements above Gadanki (13.5° N, 79.2° E) India, sho...

Figure 6.8 The Hess cycle for the complete combustion of methane, made up of...

Figure 6.9 Formation of the solar system: (a) unstable molecular cloud posse...

Figure 6.10 Evolution of the sun from a protostar, its current status as a m...

Figure 6.11 A meteorite of mostly pure iron and nickel discovered by the Mar...

Figure 6.12 Chondrules.

Figure 6.13 Decay pathways from

238

U to the two lead isotopes

210

Pb and

206

P...

Figure 6.14 The

μ

L

2

MS technique consists of (a) laser desorption follow...

Figure 6.15 A time-of-flight mass spectrometer. The arrival time of the ions...

Figure 6.16 Murchison meteorite.

Figure 6.17 Kerogen. Moderately well preserved amorphous organic matter (AOM...

Figure 6.18 Laser desorption mass spectra of extracts of the Murchison and A...

Figure 6.19 Meteorite ALH84001 – 1.93 kg of the most studied rock of all tim...

Figure 6.20 Comparison of composition and isotope data in released meteorite...

Figure 6.21 Profiling of PAH material.

Figure 6.22 The μL2MS spectrum of ALH84001: (a) from the carbonate granules;...

Figure 6.23 Fossilised structures in ALH84001.

Figure 6.24 Fossil structures in ALH84001 and Columbian basalt.

Figure 6.25 Current location (Autumn 2020) of the minor planet Veruna. Sourc...

Figure 6.26 Structure of the comet showing the nucleus, the coma, and two ta...

Figure 6.27 Tail structures of Hale-Bopp (left) and Halley (right) (1997/3/1...

Figure 6.28 Current location (Autumn 2020) of Hale-Bopp. Source: Wolframalph...

Figure 6.29 Molecules detected in experimental simulations on cometary ice a...

Figure 6.30 μL

2

MS spectra of one of the tracks (track 22) in the collection ...

Figure 6.31 (a) μL2MS spectrum of the Murchison meteorite and five stratosph...

Figure 6.32 The snow line.

Figure 6.33 Comet 67P/Churyumov-Gerasimenko by Rosetta's OSIRIS narrow-angle...

Figure 6.34 ROSINA DFMS mass spectra (9 July 2015) for masses 30, 31, 45, an...

Figure 6.35 Top (green): mass spectrum taken 25 min after first touchdown, w...

Figure 6.36 Data collected from a number of sources: the diamonds represent

Chapter 7

Figure 7.1 Structure of the solar system.

Figure 7.2 Surface gravity.

Figure 7.3 Measurements of the isotope ratios of

50

Ti/

42

Ti and

54

Cr/

52

Cr are...

Figure 7.4 Formation of the Earth: (a) the Hadean; (b) melting of the planet...

Figure 7.5 One model for the formation of the Earth-Moon systems is a collis...

Figure 7.6 Geological time periods.

Figure 7.7 Surface temperature of the Earth.

Figure 7.8 Continual habitable zone around the Sun.

Figure 7.9 Doppler shift due to the presence of a planet around a star.

Figure 7.10 Doppler profile for 51-Pegasi.

Figure 7.11 Radial velocity variations for

τ

-Bootes.

Figure 7.12 The habitable zone estimates for the promising candidate extraso...

Figure 7.13 The near infrared transmission spectrum of HD 189733b. The measu...

Figure 7.14 CO

2

concentration measured as a mole fraction of dry air is show...

Figure 7.15 NOAA measurements of CO

2

on Mona Loa. Red curves are the mean mo...

Figure 7.16 Profile of the Earth's atmosphere showing the temperature profil...

Figure 7.17 Ozone layer profile for the Earth.

Figure 7.18 Predicted changes and ground-based data of global mean ozone rel...

Figure 7.19 Oceanic zones. Source: Mitra A., Zaman S. (2020) Basics of Ecosy...

Figure 7.20 Night airglow from the international space station.

Chapter 8

Figure 8.1 A timeline from formation to the current life-forms of the Earth....

Figure 8.2 A schematic diagram of some of the ocean acidification processes:...

Figure 8.3 Miller–Urey experiments.

Figure 8.4 Strecker synthesis of amino acids.

Figure 8.5 Hydrolysis of the dipeptide glycylalanine.

Figure 8.6 Bases in DNA and RNA.

Figure 8.7 Polymerisation of HCN.

Figure 8.8 Prebiotic synthesis of cytosine and uracil.

Figure 8.9 The formose reaction.

Figure 8.10 Structure of adenosine, AMP, ADP, and ATP.

Figure 8.11 Sources of phosphorus: (a) fluorapatite; (b) the mineral schreib...

Figure 8.12 DNA and potentially information-bearing oligonucleotide analogue...

Figure 8.13 Amino acid chirality.

Figure 8.14 Homochiral snail shell.

Figure 8.15 Asymmetric photolysis of amino acids.

Figure 8.16 Bilayer structure for clay surfaces.

Figure 8.17 Geothermal vent chemical environment.

Figure 8.18 Carboxylic acid synthesis.

Figure 8.19 Proposed mechanism for the Cu

2+

/NaCl-catalysed peptide conde...

Figure 8.20 Three-step self-replication model.

Chapter 9

Figure 9.1 Toward life. Source: Adapted from Deamer 3.

Figure 9.2 Building life. Source: Adapted from Deamer 3.

Figure 9.3 Structure of a phospholipid.

Figure 9.4 Liposome bilayer structure.

Figure 9.5 Pyranene dye encapsulated in various sizes of vesicles made from ...

Figure 9.6 Encapsulation. Source: Adapted from Deamer 3.

Figure 9.7 Structure of a bacterium. Source: Reproduced from the first editi...

Figure 9.8 Passive and active membrane transport. Source: Reproduced from th...

Figure 9.9 Osmotic pressure.

Figure 9.10 The distribution of the enzyme kinetic parameters: (a)

k

cat

valu...

Figure 9.11 Common genetic ancestor. Source: Reproduced with permission from...

Figure 9.12

Deinococcus radiodurans

. Source: Reproduced with permission from...

Figure 9.13 Oxygen and ozone concentrations in the Earth's atmosphere, and t...

Figure 9.14 Energy-yielding reactions on pyrite surfaces. Source: Adapted fr...

Figure 9.15 Map of the sub-glacial lakes in Antarctica. The largest – Vostok...

Chapter 10

Figure 10.1 Impact-grazed icy surface of Europa.

Figure 10.2 Volcanic explosion on the surface of Io.

Figure 10.3 Direct biosignatures may be detected spectroscopically across th...

Figure 10.4 Comparison of modern filamentous sulfur-cycling microorganisms a...

Figure 10.5 The bioluminescence assay for ATP, producing light at 560 nm at ...

Figure 10.6 Composite image from Viking data with a pixel resolution of 1 km...

Figure 10.7 Location of the missions to Mars: Viking 1 and 2 in 1976, Pathfi...

Figure 10.8 Pathfinder image of the Martian surface.

Figure 10.9 Northern hemisphere of Titan, captured by Cassini (radar mapper ...

Figure 10.10 The albedo spectrum of Titan as measured by the instruments on ...

Figure 10.11 Schematic representation of the structures of the (a) Martian a...

Figure 10.12 The atmospheric temperature profile derived from the descent th...

Figure 10.13 A section of the IR spectrum of the Mars showing the CH

4

and H

2

Figure 10.14 The temperature profile from Titan measured by the Huygens Atmo...

Figure 10.15 Phase diagram for methane.

Figure 10.16 Chemical network based on CH

4

and N

2

.

Figure 10.17 Nitrogen polymerisation.

Figure 10.18 GC mass spectrometer data from the Huygens descent through the ...

Figure 10.19 An image from the Mars Orbiting Camera near 37.3°S, 168.0°W, in...

Figure 10.20 An image of water frost uncovered in the digging trench taken f...

Figure 10.21 A Titan coastline, seductively close to Earth-like geography...

Figure 10.22 Hyphae of

Fusarium alkanophyllum

from light hydrocarbons, produ...

Guide

Cover Page

Dedication

Title Page

Copyright

Preface to the First Edition

Preface to the Second Edition

About the Companion Website

Table of Contents

Begin Reading

Appendix A: Constants and Units

Appendix B: Astronomical Data

Appendix C: Thermodynamic Properties of Selected Compounds

Solutions to Problems

Index

WILEY END USER LICENSE AGREEMENT

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Dedicated to My Family

Astrochemistry

The Physical Chemistry of the Universe

SECOND EDITION

Andrew M. Shaw

University of Exeter

Exeter, UK

This edition first published 2022

© 2022 John Wiley & Sons Ltd

Edition History

Astrochemistry: From Astronomy to Astrobiology 1st Edition John Wiley & Sons

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Library of Congress Cataloging-in-Publication Data

Names: Shaw, Andrew M., author.

Title: Astrochemistry : the physical chemistry of the universe / Andrew M. Shaw, University of Exeter, UK.

Description: Second edition. | Hoboken, NJ : Wiley, 2022. | Includes bibliographical references and index.

Identifiers: LCCN 2020025502 (print) | LCCN 2020025503 (ebook) | ISBN 9781119114727 (hardback) | ISBN 9781119114734 (adobe pdf) | ISBN 9781119114741 (epub)

Subjects: LCSH: Cosmochemistry–Textbooks.

Classification: LCC QB450 .S53 2020 (print) | LCC QB450 (ebook) | DDC 523/.02–dc23

LC record available at https://lccn.loc.gov/2020025502

LC ebook record available at https://lccn.loc.gov/2020025503

Cover Design: Wiley

Cover Image: © ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Preface to the First Edition

Astrochemistry draws its inspiration, language, fascination, beauty, elegance, and confusion from many different disciplines: starting with astronomy, passing through physical chemistry, and ending with the new ideas of astrobiology. It is this breadth of fascination that I have attempted to capture in Astrochemistry: From Astronomy to Astrobiology. Choosing such a broad subject comes with the serious problem of how to limit the discussion of the details to allow an appreciation of the whole. I could have written an entire book on molecular astrophysics, looking at what molecules are doing in the various environments of space. I could have looked simply at the wonders of planetary chemistry, concentrating on the solar system or even just one planet such as Jupiter. Why does it have a giant red spot? Instead, I have chosen to apply a more general boundary condition for the book taking in all of the subjects but focused on the theme of ‘The Origin of Life’.

Astrochemistry starts with the origins of the Universe and the theory of the Big Bang, resulting in the formation of hydrogen, helium, and a little lithium. Gravity pulls the matter together to form stars, galaxies, and clusters of galaxies, all of which give off light in some form. The light tells the molecular story with information on the formation and evolution of stars and the role of atoms. At times these interesting subjects are buried in the disciplines of astronomy and astrophysics and I have tried to bring the pieces of the story together, concentrating on astrochemistry. The cycle of star formation ends with a supernova blowing huge quantities of material into the interstellar medium, now laden with all of the elements of the Periodic Table. Chemistry in the interstellar medium, with rather cold and tenuous conditions, is now possible and this controls the starting molecular inventory. To understand this fully, the subjects of quantum mechanics and kinetics need to be applied, through spectroscopy and chemical reaction networks, to the giant molecular clouds of the interstellar medium – the birthplace of stars and life?

Giant molecular clouds collapse to form stars and solar systems, with planets and debris left over such as comets and meteorites. Are comets and meteorites the delivery vehicles that enable life to start on many planets and move between the planets as the solar system forms, providing water and molecules to seed life? The planets have to be hospitable, however, and that seems to mean wet and warm. Carbon-based life forms and liquid water seem to be the successful life-experiment on Earth from which we can draw some more general conclusions about the requirements for life in a view towards astrobiology. A look at prebiotic chemistry and primitive life forms on Earth poses interesting questions such as what is a cell and how big does it have to be? The guiding principles for prebiotic chemistry are the laws of thermodynamics that keep the origins of life and its understanding on the straight and narrow.

Finally, and tantalizingly for this book and astrochemistry, there is Titan. The Cassini–Huygens mission is now in orbit in the Saturnian system as the book is published. The Huygens probe has already made the descent to the surface of Titan and the data have been transmitted back successfully. Scientists, astronomers, astrochemists, and astrobiologists are trying to understand it. I have taken a brief look at Titan as a case study to apply all that has been learnt and to review the possibilities for astrochemistry in what is surely to be a very exciting revelation of the structure and chemistry of Titan.

Throughout the book I have tried to constrain the wonders of imagination inspired by the subject by using simple calculations. Can all of the water on the Earth have been delivered by comets: if so, how many comets? How do I use molecular spectroscopy to work out what is happening in a giant molecular cloud? Calculations form part of the big hard-sell for astrochemistry and they provide a powerful control against myth. I have aimed the book at second-year undergraduates who have had some exposure to quantum mechanics, kinetics, thermodynamics, and mathematics but the book could easily be adapted as an introduction to all of these areas for a minor course in chemistry to stand alone.

Units and Conventions

Astronomy is probably the oldest of the subjects that influence astrochemistry and contains many ancient classifications and unit systems that have been preserved in the scientific research of today. Distances are measured in light-years or parsecs, neither of which are the standard SI unit of length: the metre. This is not surprising when a light-year is 9.5 × 1015 m and is a relatively small astronomical unit of length! The correct SI convention for a light-year would be 9.5 petametres, written as 9.5 Pm. This is formally correct but would not help you in a conversation with anybody, as most scientists cannot remember the SI prefixes above 1012. I have listed the SI prefixes in Appendix A and we shall use them where appropriate. However, I will use two units of length chosen from astronomy, namely the light-year and the astronomical unit. The light-year is the distance travelled by light in 1 year or 86 400 s and 1 ly is 9.5 Pm or 9.5 × 1015 m. Usefully, the distance to the nearest star is some 4 ly. The other length unit is the astronomical unit (AU), which is the average distance from the Earth to the Sun and is 1.49 × 1011 m, with the entire solar system being approximately 150 000 AU and the distance to the nearest star some 300 000 AU.

The unit of time is the second in the fundamental list of constants but it is convenient to use years when referring to the age of the Universe, Solar System or the Earth. I have chosen to use the SI prefixes in front of the symbol yr so that 109 years is 1 Gyr; the age of the Universe is 15 billion years or 15 Gyr, etc., and whenever this refers to a period of time in the past then 4.5 Gyr ago will be used explicitly.

The conventions of chemistry, particularly physical chemistry, are standard and appear in all physical chemistry textbooks and will be used here. The same courtesy has been extended to organic and inorganic chemistry and biology, so that the ideas of these subjects can be linked into the common theme.

Course Material

I have put together a website for the book (www.wiley.co.uk/shawastrochemistry) where I have included the figures from the book to be downloaded into lectures. I have also included some links that I have found useful, corrections when required even some possible examination questions. I hope an adventurous professor will find these useful.

Acknowledgements

The book started as a survey of the literature to identify a research project, which in part it did, but during the work I discovered how interesting the subject can be and decided that it would make a good lecture course. The long-suffering students at the Department of Chemistry at Exeter University have enjoyed the course on two separate occasions and in two incarnations, most latterly as CHE2057 in 2005. The students saw the book at first draft and have contributed to removing the mistakes and suggested additions, pointing out where I said too much or too little. The refinements have helped and improved the text immeasurably. I have doubtlessly introduced more mistakes and for this I must take the full credit. The integrity of the book has been improved greatly by two very conscientious reviewers, to whom I owe a debt of gratitude. I must extend thanks to all scientists around the world who helped to put together the figures for the book. Busy people spent valuable time collecting the images that have added to the wonder of the subject. The reward for writing the book will be the spark of curiosity that may flicker in the mind of the reader.

Andrew M. Shaw

Preface to the Second Edition

There are many reasons to update a textbook, the most important of which is that it gets out of date – at its core, it should be research-led. Astrochemistry and astrobiology have advanced significantly as fields driven by some truly remarkable planetary exploration science and astronomy. The Cassini-Huygens mission to the Saturnian moon Titan, hinted at in the first edition, sent back data to Earth with such extraordinary detail that I could not resist including an extended review of this hydrocarbon world. Similarly, the Mars rovers have now explored 31.81 miles on the Martian surface (Spirit 4.80 miles, and Opportunity 27.04 miles) at a sedate 12 miles per hour, digging up some interesting finds and consequences. We have also flown by Pluto for the first time, with the closest approach on 14 July 2015, changing Pluto from a 4-pixel world seen through the Hubble Space Telescope to a mysterious non-planet. Visits to asteroids, revisiting Mercury, discovering the Higgs boson, landing on a comet, the increased energy of the Large Hadron Collider, dark matter, Martian meteorites – this massively impressive list is a tribute to human endeavour and raw curiosity. It's important to track down these stories, and I have now referenced them throughout the book (not exhaustively, of course).

The principles of physical chemistry are universal, however, and their application to these new challenges is compelling – as was the change in the book's subtitle, The Physical Chemistry of the Universe. The application of physical chemistry to a diverse selection of research fields, seemingly unlinked at first, shows how a quantitative, mechanistic, deterministic approach to a problem is the best way to understand what is happening. In Chapter 5, I have developed the idea of deterministic models for interstellar medium chemistry that can be applied rigorously to atmospheres, interfaces, and surface and systems biology. This mechanistic approach is central to my research group, my spin-out companies, and the philosophy of the book. Inevitably, it involves some mathematics and coding in a high-level language such as Mathematica, WolframAlpha, or Matlab.

But physical chemistry is not a spectator sport, and the mathematics, calculations, and models must be tested using high-quality data, which involves hard mathematics. But surely mathematics is a ‘done deal’ given all of the powerful mathematics packages available? This may sound heretical, but algebra, integration, and differentiation can all be performed analytically using the computer packages; and the new, evolving physical chemistry skill is knowing how to set up a model and then how to test it – the implementation is almost a given. Knowledge itself is being computed, and there are now knowledge engines such as WolframAlpha that provide great power. Not only can it check the mathematics, but it can also answer questions and solve problems. I have incorporated references to WolframAlpha throughout the book, sometimes as interesting bits of information, other times as access to primary sources of data such as the NIST Atomic Spectra Database.

In addition to the book in paper form (which still provides a visceral human reading experience), the book is also available as an eBook, making the WolframAlpha links directly accessible. Completing the knowledge engine approach to the second edition is a set of CDF files on the website, supporting each of the chapters. These examples allow the reader to interact with the equations, change parameters, and derive information from the models. Similar interfaces are available in many complex modelling programmes and let the reader explore the model without the mathematical burden.

As you read the book and explore physical chemistry, consider the hypothesis that chemistry is fundamentally the interactions of energy and shape. Shape includes all the ideas of quantum mechanics: special allowed shapes and transitions, but also the idea that time is a shape the space-time dimension of special relativity (specifically, ict). Add energy to evolving shape, and there is a reasonable hypothesis for all of chemistry: extensions to astrochemistry and astrobiology are exciting examples.

The format of the book has changed: it is now larger and in full colour. Twenty problems are included at the end of each chapter, with some detailed solutions to give the reader the chance to exercise their mathematics (which becomes rusty very quickly if not used). I have added new sections on thermodynamics using meteor entry and included enzyme kinetics in the prebiotic lifeforms.

Acknowledgements

Thank you to all those students who have taken the course with me and provided feedback; the Norman Lockyer observatory, for making astronomy real; Dr Peter Reader, for some CDF files; Wiley, for commissioning the second edition; and, critically, all of the people who bought the first edition. Countless texts and papers have influenced my thoughts; to those authors, my apologies if you have not been referenced fully.

Andrew M. Shaw

Winter, 2020

About the Companion Website

This book is accompanied by a companion website:

www.wiley.com/go/shaw2e

The website includes:

PPTs of all the figures

A selection CDFs relevant to each Chapter

Chapter 3

- Video clip of the Pillars of Creation in 3D:

https://www.ras.org.uk/news-and-press/2623-the-pillars-of-creation-in-3d

Scan this QR code to visit the companion website.

1The Molecular Universe

Chemistry without numbers is poetry: astrochemistry without numbers is myth. A molecule placed around a star, in a nebula, lost in the interstellar medium, on a planet or within a cell has the potential for very complex and beautiful chemistry but unless we can understand the local conditions and how the molecule interacts with them, we have no idea what chemistry is really happening. To understand astrochemistry we need to understand the physical conditions that occur within the many diverse molecular environments. The exploration of the molecular universe will take us on a long journey through the wonders of astronomy to the new ideas of astrobiology but as we look out of the window, the physical chemistry of the Universe will continually challenge us and cause us to question everything.

The origins of life provide the motivation and excuse to investigate astrochemistry in its broadest sense, looking at molecules and their local complex chemistry using all of the tools of physical chemistry to constrain the imagination of the astrobiologist in the field and to force a re-think of the rules of biology that are prejudiced by the experience of life on Earth. The complexity of the problem places demands on the theories of science, stretching the understanding of kinetics and thermodynamics into areas where large non-ideal systems are hard to understand, although curiously, modelling the complex chemistry of a giant molecular cloud is not dissimilar to the models of biochemistry within a cell. The size of the chemical problem quickly grows, so that the chemistry of 120 molecules in a giant molecular cloud must be compared with the 4500 reactions thought to be required to make a cell work. The real understanding of the molecular mechanism only comes from a model of the network of coupled chemical equations forming a complex system: something as comparatively simple as a candle flame can contain 350 equations.

Our mission is to explore the molecular universe to develop an understanding of all the local molecular environments, constrain possible chemical reactions using the concepts of physical chemistry, and understand the potential for life on other worlds.

1.1 The Standard Model – Big Bang Theory

About 13.772 ± 0.059 billion years ago [1, 2] the Universe and time itself began in a Big Bang [3]. This is an impressively accurate number with a quantified error, music to the ears of a quantitative scientist such as a physical chemist. We shall see at various points how this number has become so accurate thanks to, amongst others, observations of the cosmic microwave background by the NASA Wilkinson Microwave Anisotropy Probe (WMAP) (http://map.gsfc.nasa.gov).

Observations of the night sky show that stars and galaxies are moving away from us, telling us that the Universe is expanding: extrapolating backwards in time leads to a point of common beginning, a singularity in space-time known as the Big Bang. A simple theory containing six parameters fits all of the current cosmological data [4]: the age of the universe, the density of atoms, the density of matter, the amplitude of the initial fluctuations, the scale dependence of this amplitude, and the epoch of first star formation. Along each line of sight observed by the WMAP satellite there is the history of the universe (Figure 1.1), from the period of uncertainty, the Planck epoch, through a massive inflation 180-e fold (e being the base of natural logarithms) during which very high-energy photons collided with one another, cooling at each collision until what is left is the cosmic microwave background (see Section 2.2). This afterglow is a snapshot of what was left after the first 375 000 years.

Temperature is critical to the phases of evolution and subsequent cooling of the Universe, producing a number of critical times, detailed in Table 1.1. They are all predictions of the Big Bang Theory or the Standard Model of Cosmic Evolution [3].

Einstein's theory of relativity allows for the interconversion of energy and matter through the famously simple equation E = mc2. Thus, collisions between high-energy photons in the primordial fireball created particle–antiparticle pairs such as protons and antiprotons. After some 180 s and at a temperature of 109 K atomic nuclei such as hydrogen, deuterium, helium and some lithium were formed. The first three minutes of all time were chemically the dullest with no atoms or molecules. For a further 106 s the light atoms continue to be formed, marking a period where matter is created by Big Bang nucleosynthesis.

Figure 1.1 The cosmic timeline as it is observed today by the Wilkinson Microwave Anisotropy Probe (WMAP), which is studying the cosmic microwave background. The inflation cone shows what is happening/happened along one line of sight: they are obviously in all possible 4π-solid angle directions.

Table 1.1 The history of the Universe according to the Standard Model

Source: Based on Ratra and Vogeley [3].

Time since

t =

 0

Temperature

Comments

10

–43

s

   10

32

 K

Gravity is now distinct from the three other forces: strong, weak nuclear and electromagnetic.

10

–35

s

   10

27

 K

Inflation of the Universe – the strong force separates.

10

–12

s

   10

15

 K

Weak and electromagnetic forces separate. Neutrons and protons are formed by photon-photon collisions.

10

–2

s

   10

11

 K

Electrons and positrons are formed through collisions of photons.

1 s

   10

10

 K

The Universe becomes transparent to neutrinos.

180 s

   10

9

 K

Nucleosynthesis: hydrogen, deuterium, helium and some lithium.

3–7 × 10

5

s

   3000 K

Light element atoms form, and the Universe is now transparent to radiation: cosmic background is emitted.

10

9

yr

   20 K

Galaxies form.

Present

   2.726 K

Stars and galaxies.

Figure 1.2 The proportions of each component of the Universe. Exact proportions are changing as the theories evolve, but astrochemistry comprises at most 5% of the universal problem. Source: Adapted from David N. Spergel [4].

There are a number of astronomical pieces of evidence for the Big Bang Theory as we shall see, including the recent observation of the cosmic microwave background radiation but it is far from a complete theory [1, 3, 5]. However, predictions of the theory may be tested. One such prediction is the relative abundance by mass of He, which must be at least 25% of the total mass. Helium is also made in stars and must contribute to the He density of the Universe and in all observations to date the observed abundance is greater than 25%. There are problems associated with matter. Why is the Universe made from matter instead of antimatter? When was this decision made to stabilise matter from high-energy photons and particle–antiparticle pairs. Further, calculations of gravitational attractions of galaxies suggest the presence of large amounts of matter that cannot be seen, so-called dark matter. What is dark matter? The current assessments of the relative portions of these rare cosmological substances is shown in Figure 1.2, although they are only the current estimates based on theories and rather fewer observations [4]. Astrochemistry makes up at most 5% of the problem.

The majority of the atomic Universe is made from hydrogen and helium produced during the Big Bang, although some He has been made subsequently. The relative cosmic abundance of some of the elements relevant to the formation of life is given in Table 1.2, with all elements heavier than H, He and Li made as a result of fusion processes within stars, as we shall see later. The cosmic abundance is assumed to be the same as the composition of the Sun.

Table 1.2 Relative cosmic abundance of the elements

Element

Relative abundance

Element

Relative abundance

H

1

S

1.6 × 10

–5

He

0.085

P

3.2 × 10

–7

Li

1.5 × 10

–9

Mg

3.5 × 10

–5

C

3.7 × 10

–3

Na

1.7 × 10

–6

N

1.2 × 10

–3

K

1.1 × 10

–7

O

6.7 × 10

–3

Si

3.6 × 10

–6

1.2 Galaxies, Stars, and Planets

After the initial photon collisions and formation of matter, all matter formed in the Big Bang is attracted to itself by the force of gravity, which finally results in the formation of the first proto-stars before there is any starlight. This period is called the epoch of first star formation or the dark ages. Within 1 billion years, the first massive proto-galaxies form. Gravitational contraction continues in more and more localised regions to form the galaxies we know today, including our galaxy, the Milky Way. The Milky Way, shown in Chapter 2, Figure 2.15, is in a cluster of galaxies called the local group (Figure 2.19), which includes the Large Magellanic Cloud, the Small Magellanic Cloud, and the Andromeda Galaxy (M31; Figure 2.15). Two of these, the Milky Way and the Andromeda Galaxy, are very luminous spiral galaxies.

Large Magellanic Cloud

Small Magellanic Cloud

Andromeda Galaxy (M31)

Milky Way

The Milky Way was formed within 1 billion years of the Big Bang and has a mass of 109 solar masses. It formed from a large cloud of hydrogen and helium that was slowly rotating. As the cloud collapsed, conservation of angular momentum required matter near the axis to rotate very fast. As a result, it spreads away from the axis and forms a flat spiralled disc some 120 000 ly in diameter and about 3300 ly thick. The Sun is approximately 30 000 ly from the centre. The nuclear bulge at the core of the galaxy contains old stars, and observations suggest that it must be hugely massive. Rapid rotation around the axis of the disc requires gravity and angular momentum, hence mass, to hold it together and this produced speculation about the existence of a black hole at the centre of the Milky Way.

The Sun formed some 4.5 Gyr ago (Gyr is a gigayear or 109 years) from its own gas cloud called the solar nebula, which consisted of mainly hydrogen but also all of the heavier elements that are observed in the spectrum of the Sun. Similarly, the elemental abundance on the Earth and all of the planets was defined by the composition of the solar nebula and so was ultimately responsible for the molecular inventory necessary for life. The solar system formed from a slowly rotating nebula that contracted around the proto-sun, forming the system of planets called the solar system. Astronomers have recently discovered solar systems around other stars, and in only the briefest of looks, this has revealed a large proportion of similar planetary systems: the formation of planets around stars is a common process. The distribution of mass in the solar system is primarily within the Sun but distributed rather differently among the planets. The inner planets, the so-called terrestrial planets of Mercury, Earth, Venus, and Mars, are essentially rocky; but Jupiter, Saturn, Uranus, and Neptune are huge gas giants. This needs to be explained by the formation process. Most important, however, is the formation of a planet in a habitable zone, where liquid water can exist and have the potential for life – at least if you follow the terrestrial model.

1.3 Origins of Life

The age of the Earth is established by radioisotope dating at 4.55 Gyr. For most of the first billion years it suffered major impact events capable of completely sterilising the Earth, removing any life forms – mass-extinction events. The geological fossil records reveal, however, that life existed some 3.5 Gyr ago and perhaps as early as 3.9 Gyr ago. The oldest known life forms were very simple by modern standards but already had hugely complicated structures involving membranes and genetic information. The rather surprising conclusion is that life may have developed in as little as 100 million years and at most 0.5 billion years, to evolve from the primordial soup to a viable living organism that had adapted to its local environment.

1.3.1 Definitions of Life

There are many problems with the definitions of life [6], although determining what is alive and what is not is intuitively easy. At the extremes of collections of matter are human beings and atoms, with all of the possibilities in between and beyond. Classical definitions of life taken from biology, such as ingesting nutrients, excreting by-products, growth, and reproduction, all serve as good markers of life, although they are almost certainly prejudiced by life on Earth. What about fire? A candle flame (Figure 1.3) clearly ingests nutrients from the air in the form of oxygen and fuel from the wax. It produces waste products; it can also grow to cover large areas and certainly looks as if it might reproduce itself by creating new fires through sparks. It is localised by both a temperature and a concentration gradient and might indeed be alive. However, one flame does become a copy of itself in that it will burn whatever fuel and oxidant combination available to it. In a sense, it evolves and lives for as long as it can adapt to its environment. The adaptation to the environment is seen on the right-hand side of Figure 1.3, where a candle flame is burning under conditions of zero gravity in the space shuttle. The shape of the flame in air is controlled by buoyancy: the hot air inside the candle flame air is less dense than the air around it, and it rises. In zero gravity the hot air does not rise, because its weight is zero, and so the random thermal motion results in diffusion of oxygen into the flame and combustions products away from the flame; hence the flame is now spherical. Even a complex set of chemical reactions, recognisable as a flame, has adapted to the environment. There is a consistent chemistry set within the 350 equations required to get the flame ‘metabolism’ chemistry to burn properly and, as such, it contains a recipe or DNA. Other more impressively vague twilight life forms must include virus particles.

Figure 1.3 Two species of candle flame – dead or alive? The flame on the left is on Earth, and the flame on the right is burning under zero gravity. Source: Photos by courtesy of NASA.

Viruses have no real metabolism and appear to exist in a dormant state until they find a suitable host. Then they hijack the metabolism and DNA replication apparatus of the host cell, switching the host into the production of huge numbers of copied virus particles, including some mutations for good measure. Finally, the cell bursts and the virus particles are released to infect a new host. The propagation of genetic information is important, as is the need for some form of randomisation process in the form of mutations, but it is not clear that there can be one definition for life itself. NASA has chosen the following definition:

Life is a self-sustained chemical system capable of undergoing Darwinian evolution.

Alternatively, my definition in the first edition was:

A system that is capable of metabolism and propagation of information.

And this remains reasonable. Others are equally struck by the concept of information propagation [6].

1.3.2 Specialisation and Adaptation