11
These estimates are based on the observed high correlation between current discoveries of giant extrasolar planets and the metallicity (enrichment in heavy elements) of their parent stars. D. Fischer and J. Valenti, “The Planet-Metallicity Correlation,”
Astrophysical Journal
622 (2005): 1102. Planet formation seems to go much more efficiently once the metallicity reaches at least a tenth of that in the Solar System. Continued searches for planets in old environments poor in heavy elements (the globular cluster 47 Tuc, halo stars) have failed to find planets. Gilliland et al., “A Lack of Planets in 47 Tucanae from a Hubble Space Telescope Search,”
Astrophysical Journal
545 (2000): 47; Sozzetti et al., “A Keck.” Evidence relevant to rocky planets will emerge from the Kepler mission, when the mission tallies its findings and statistical analysis, in a few years. For the time being, preliminary results summarized in papers by W. Borucki et al., “Characteristics of Planetary Candidates Observed by Kepler. II. Analysis of the First Four Months of Data,”
Astrophysical Journal
736 (2011): 19, and A. Howard et al., “Planet Occurrence Within 0.25 AU of Solar-type Stars from Kepler,”
Astrophysical Journal,
preprint, ArXiv: 1103.2541 (2011), show that the trend with stellar metallicity is
still there, though it appears less pronounced than the trend for giant hot Jupiters.
12
The literature on the Fermi paradox is vast, but Paul Davies offers a thorough and very thoughtful discussion in his excellent new book
The Eerie Silence
(New York: Houghton Mifflin Harcourt, 2010).
13
The estimate was introduced in Bennett et al.,
The Cosmic Perspective
(Boston: Addison-Wesley, 2007).
14
Our Kepler team made this estimate in a paper (Howard et al., “Planet Occurrence”), but only for candidate super-Earth-size planets discovered by Kepler close to their stars (within 0.25 Astronomical Unit).
15
Madau et al., “The Star Formation History of Field Galaxies,”
Astrophysical Journal
498 (1998): 106, plotted the star formation rate versus red shift.
CHAPTER TWELVE
1
H. J. Melosh, “Exchange of Meteorites (and Life?) Between Stellar Systems,”
Astrobiology
3 (2003): 207, explores the issue in detail and concludes that interstellar trips of meteorites are very unlikely, while exchange between planets in the same system is common.
2
For example, A. Foster and G. Church, “Towards Synthesis of a Minimal Cell,”
Molecular Systems Biology
2 (2006): 1, describe the “recipe” for making a living cell ab initio. A press release by the J. C. Venter Institute dated January 24, 2008, describes the completion of the full synthetic genome of a microbe provisionally named
Mycoplasma genitalium
JCVI-1.0; published in D. G. Gibson et al., “Complete Chemical Synthesis, Assembly, and Cloning of a
M. genitalium
Genome,”
Science
319 (2008): 1215. This was a major step that eventually led the same team to the
creation of a bacterial cell controlled by a chemically synthesized genomeâ
Mycoplasma mycoides
JCVI-syn1.0 (Gibson et al., “Creation of a Bacterial Cell Controlled by a Chemically Synthesized Genome,”
Science
329 [2010]: 53). See also P. Berry, “Life from Scratch,”
Science News,
January 12, 2008.
3
Pier Luigi Luisi, “The Synthetic Approach in Biology: Epistemological Notes for Synthetic Biology,” in
Chemical Synthetic Biology,
ed. P. L. Luisi and C. Chiarabelli (Hoboken, NJ: John Wiley, 2011), 343; John Brockman, ed.,
Life: What a Concept!
(New York:
Edge.org
, 2008).
4
The term “synthetic biology” seems to have been introduced by W. Szybalski in 1974 in
Control of Gene Expression,
ed. A. Kohn and A. Shatkay (New York: Plenum, 1974), according to S. Benner et al., “Synthetic Biology, Tinkering Biology, and Artificial Biology: A Perspective from Chemistry,” in
Chemical Synthetic Biology,
ed. P. L. Luisi and C. Chiarabelli (Hoboken, NJ: John Wiley, 2011), 69. It was reused by Barbara Hobom in “Surgery of Genes: At the Doorstep of Synthetic Biology,”
Medizinische Klinik
75 (1980): 14, and then reutilized by Eric Kool (Stanford) and others in 2000, though with somewhat different connotations. A comprehensive technical review of synthetic biology in all its different forms appears in
Nature Review's Genetics
6 (2005): 533, “Synthetic Biology,” by S. Benner and A. M. Sismour. A nontechnical review by Ed Regis appears in his nice book on the subject,
What Is Life? Investigating the Nature of Life in the Age of Synthetic Biology
(New York: Farrar, Straus & Giroux, 2008). My definition of “synthetic biology” is not the widely used one as of the time of this writing, though it is essentially the same as “chemical synthetic biology” discussed by Pier Luigi Luisi and by Steven Benner in their essays in the recent compilation
Chemical Synthetic Biology,
ed. P. L. Luisi and C. Chiarabelli (Hoboken, NJ: John Wiley, 2011). The field and its language remain largely in flux. We need a new vocabulary for the novel concepts that are being introduced with its rapid development.
5
P. Luigi Luisi, “Chemical Aspects of Synthetic Biology,”
Chemistry and Biodiversity
4 (2007): 603.
6
For a detailed, accessible discussion of minimal cell definitions and the rich history of the concept, see Regis,
What Is Life?
My colleagues Jack Szostak and George Church are working on different approaches, but they encompass the conceptual framework of the synthesis. J. Szostak, D. Bartel, and P. Luigi Luisi, “Synthesizing Life,”
Nature,
January 18, 2001; and A. Forster and G. Church, “Towards Synthesis of a Minimal Cell,” 1.
7
There is some tantalizing evidence that cosmic and planetary environments might influence the choice of symmetry of some biomolecules; see D. Glavin and J. Dworkin, “Enrichment of the Amino Acid L-isovaline by Aqueous Alteration on CI and CM Meteorite Parent Bodies,”
Proceedings of the National Academy of Science USA
106 (2009): 5487.
8
A mirror system might allow molecular biology experiments that suffer from less contamination and are easier to perform to high fidelity. If minimal cells can be maintained, their accelerated evolution might teach us the basics of designing a minimal genome, akin to what Jack Szostak refers to as a “protocells arms race.” J. Szostak, “Learning About the Origin of Life from Efforts to Design an Artificial Cell,” Konrad Bloch Lecture, Harvard University, November 23, 2010. Such a genome might be central to the transition from prebiotic chemistry to biochemistry.
9
Examples of this approach that are relevant to origins of life research are the pioneering work of the A. Eschenmoser Group, for example, A. Eschenmoser, “Searching for Nucleic Acid Alternatives,” in
Chemical Synthetic Biology,
ed. P. L. Luisi and C. Chiarabelli, (Hoboken, NJ: John Wiley, 2011), 12. Breakthrough work on nucleotides synthesis in prebiotically plausible planetary conditions was done by the J. Sutherland Group. M. Powner, B. Gerland, and J. Sutherland, “Synthesis of Activated Pyrimidine Ribonucleotides in Prebiotically Plausible Conditions,”
Nature,
May 14, 2009.
10
Generation II life is different from Generation I evolving (via cultural evolution) to a postbiological state, as discussed by Steven Dick, “Cultural Evolution, the Postbiological Universe, and SETI,”
International Journal of Astrobiology
2 (2003): 65, and references; or the “closer to us humans who transcend biology” of Ray Kurzweil or the Homo evolutis of Juan Enriquez.
11
The story follows the research done after the discovery of well preserved mummies in burials dating 3,000â4,000 years ago in the Tarim basin, around several ancient cities that later became an essential part of the Silk Road, as described in J. Mallory and V. Mair,
The Tarim Mummies
(London: Thames & Hudson, 2000).
12
Sven Hedin,
Der Wanderde See,
2nd ed. (Leipzig: Brockhaus, 1941).
13
J. Mallory and V. Mair,
The Tarim Mummies
.
INDEX
Absorption lines, spectrum
Amino acid
Ammonia
Arrhenius, Svante
Artificial cells
Astronomical unit
Atmosphere (planetary)
Bakos, Gaspar
Basalt
Beaulieu, J.-P.
Biochemistry
Bonds,
chemical
weak
Borucki, William
Brown dwarf
Brown, Tim
Brownlee, Donald
Butler, Paul
Camera
Carbonate-silicate cycle
See also
CO
2
cycle
Carbon dioxide
Cells
Charbonneau, David
Chemical landscape
Church, George
Civilizations
Columbus, Christopher
Convection
Cook, James
Copernican revolution
Core-mantle boundary
D” layer
Core (planetary)
CoRoT mission
CoRoT-7
Cosmic microwave background (CMB)
Crust (planetary)
Darwin, Charles
Darwin project (ESA)
Davies, Paul
Deep biosphere
Deinococcus radiodurans
Dick, Steven
Differentiation (planetary)
Disk (proto-planetary)
DNA
Doppler effect
Doppler shift,
See
Method, Doppler shift
Doppler wobble,
See
Method, Doppler shift
Earthquakes
Eclipse (planets)
Eclipse (stars)
Einstein, Albert
Electromagnetic waves
Electrons
Elements, chemical
origin
Enriquez, Juan
Enzymes
Eratosthenes
Evolution,
Darwinian
of the atmosphere
stellar
theory of
Extremophiles
False positives
Fermi, Enrico
Fermi paradox
51 Peg
Force(s)
electromagnetic
gravitational
Frail, Dale
Gassendi, Pierre
Generation I and II life
Genetic molecules
Geochemical cycle
Geological timescale
GJ1214
Gibson, D.G.
Gliese
Gliese
Gliese
Goldilocks hypothesis
Granite
Greenhouse gas
HAT (project)
HD
HD
HMS
Challenger
HR8799
Habitable planets
Habitable potential
Habitable zone
Handedness
Hart, Michael
Homo sapiens
Home evolutis
Horowitz, Paul
Horrocks, Jeremiah
Howard, Andrew
Hoyle, Fred
Humboldt, Alexander von
Hydrogen
Hydrogen sulfide
Jha, Saurabh
Joyce, Gerald
Jupiter
hot
-like
super-
Initial conditions
Kaltenegger, Lisa
Kant-Laplace model
Kasting, James
Kepler, Johannes
Kepler's laws of planetary motion
Kepler's law of planetary volumes
Kepler mission (NASA)
Kepler-11
Knoll, Andrew
Konacki, Maciej
Kulkarni, Shri
Kurzweil, Ray
Latham, David
Life,
definition
Light
infrared
visible
UV
Lissauer, Jack
Mantle (planetary)
Marcy, Geoffrey
Mars
Martian meteorites
Mason, Charles and Dixon, Jeremiah (Mason-Dixon Line)
Mayor, Michel
Mercury
transit of
MEarth (project)
Meteorites
Methane
Method (for planet discovery)
astrometry
direct imaging
Doppler shift
gravitational lensing
timing
transit
wobble.
See
Method, astrometry, Doppler shift
Microbes
Minimal artificial cell
Mirror life
Miller, Stanley
Moravec, Hans
Mycoplasma mycoides JCVI-syn1.0
Neptune
hot
mini-
-like
Newton, Isaac
Nisenson, Peter
O'Connell, Richard
OGLE (team)
OGLE-TR-33
OGLE-TR-56
OGLE-2005-BLG-390Lb
Oganov, A.
Olivine
Ono, S.
Orbital eccentricity
Orbital inclination
Orbital period
Orbital speed
Origins of life
Paczynski, Bohdan
Panspermia
Papaliolios, Costas
Perovskite
Photometry
Photons
Planet-metallicity trend
Planets
Earth-like
carbon
dwarf
exo
extrasolar
gas giant
habitable
ocean
pulsar
rocky
terrestrial
transiting
with habitable potential