101
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Gleiser M, Nelson BJ, Walker SI. Chiral polymerization in open systems from chiral-selective reaction rates. ORIGINS LIFE EVOL B 2012; 42:333-46. [PMID: 22610131 DOI: 10.1007/s11084-012-9274-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2012] [Accepted: 04/25/2012] [Indexed: 10/28/2022]
Abstract
We investigate the possibility that prebiotic homochirality can be achieved exclusively through chiral-selective reaction rate parameters without any other explicit mechanism for chiral bias. Specifically, we examine an open network of polymerization reactions, where the reaction rates can have chiral-selective values. The reactions are neither autocatalytic nor do they contain explicit enantiomeric cross-inhibition terms. We are thus investigating how rare a set of chiral-selective reaction rates needs to be in order to generate a reasonable amount of chiral bias. We quantify our results adopting a statistical approach: varying both the mean value and the rms dispersion of the relevant reaction rates, we show that moderate to high levels of chiral excess can be achieved with fairly small chiral bias, below 10%. Considering the various unknowns related to prebiotic chemical networks in early Earth and the dependence of reaction rates to environmental properties such as temperature and pressure variations, we argue that homochirality could have been achieved from moderate amounts of chiral selectivity in the reaction rates.
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Affiliation(s)
- Marcelo Gleiser
- Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755, USA.
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102
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Groen J, Deamer DW, Kros A, Ehrenfreund P. Polycyclic aromatic hydrocarbons as plausible prebiotic membrane components. ORIGINS LIFE EVOL B 2012; 42:295-306. [PMID: 22798228 PMCID: PMC3427487 DOI: 10.1007/s11084-012-9292-3] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2012] [Accepted: 06/21/2012] [Indexed: 12/02/2022]
Abstract
Aromatic molecules delivered to the young Earth during the heavy bombardment phase in the early history of our solar system were likely to be among the most abundant and stable organic compounds available. The Aromatic World hypothesis suggests that aromatic molecules might function as container elements, energy transduction elements and templating genetic components for early life forms. To investigate the possible role of aromatic molecules as container elements, we incorporated different polycyclic aromatic hydrocarbons (PAH) in the membranes of fatty acid vesicles. The goal was to determine whether PAH could function as a stabilizing agent, similar to the role that cholesterol plays in membranes today. We studied vesicle size distribution, critical vesicle concentration and permeability of the bilayers using C6-C10 fatty acids mixed with amphiphilic PAH derivatives such as 1-hydroxypyrene, 9-anthracene carboxylic acid and 1,4 chrysene quinone. Dynamic Light Scattering (DLS) spectroscopy was used to measure the size distribution of vesicles and incorporation of PAH species was established by phase-contrast and epifluorescence microscopy. We employed conductimetric titration to determine the minimal concentration at which fatty acids could form stable vesicles in the presence of PAHs. We found that oxidized PAH derivatives can be incorporated into decanoic acid (DA) vesicle bilayers in mole ratios up to 1:10 (PAH:DA). Vesicle size distribution and critical vesicle concentration were largely unaffected by PAH incorporation, but 1-hydroxypyrene and 9-anthracene carboxylic acid lowered the permeability of fatty acid bilayers to small solutes up to 4-fold. These data represent the first indication of a cholesterol-like stabilizing effect of oxidized PAH derivatives in a simulated prebiotic membrane.
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Affiliation(s)
- Joost Groen
- Leiden Institute of Chemistry, Leiden University, 2333 CC Leiden, The Netherlands.
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103
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Johnson BC, Melosh HJ. Impact spherules as a record of an ancient heavy bombardment of Earth. Nature 2012; 485:75-7. [PMID: 22535246 DOI: 10.1038/nature10982] [Citation(s) in RCA: 101] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2011] [Accepted: 02/21/2012] [Indexed: 11/09/2022]
Abstract
Impact craters are the most obvious indication of asteroid impacts, but craters on Earth are quickly obscured or destroyed by surface weathering and tectonic processes. Earth’s impact history is inferred therefore either from estimates of the present-day impactor flux as determined by observations of near-Earth asteroids, or from the Moon’s incomplete impact chronology. Asteroids hitting Earth typically vaporize a mass of target rock comparable to the projectile’s mass. As this vapour expands in a large plume or fireball, it cools and condenses into molten droplets called spherules. For asteroids larger than about ten kilometres in diameter, these spherules are deposited in a global layer. Spherule layers preserved in the geologic record accordingly provide information about an impact even when the source crater cannot be found. Here we report estimates of the sizes and impact velocities of the asteroids that created global spherule layers. The impact chronology from these spherule layers reveals that the impactor flux was significantly higher 3.5 billion years ago than it is now. This conclusion is consistent with a gradual decline of the impactor flux after the Late Heavy Bombardment.
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Affiliation(s)
- B C Johnson
- Department of Physics, Purdue University, 525 Northwestern Avenue, West Lafayette, Indiana 47907, USA.
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104
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Joy KH, Zolensky ME, Nagashima K, Huss GR, Ross DK, McKay DS, Kring DA. Direct Detection of Projectile Relics from the End of the Lunar Basin–Forming Epoch. Science 2012; 336:1426-9. [DOI: 10.1126/science.1219633] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- Katherine H. Joy
- Center for Lunar Science and Exploration, Lunar and Planetary Institute, Universities Space Research Association, 3600 Bay Area Boulevard, Houston, TX 77058, USA
- NASA Lunar Science Institute
| | - Michael E. Zolensky
- NASA Lunar Science Institute
- ARES, NASA Johnson Space Center, Houston, TX 77058 USA
| | - Kazuhide Nagashima
- Hawai‘i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, HI 96822, USA
| | - Gary R. Huss
- Hawai‘i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, HI 96822, USA
| | - D. Kent Ross
- ARES, NASA Johnson Space Center, Houston, TX 77058 USA
- Engineering and Science Contract Group, Jacobs Technology, 2224 Bay Area Boulevard, Houston, TX 77058, USA
| | - David S. McKay
- NASA Lunar Science Institute
- ARES, NASA Johnson Space Center, Houston, TX 77058 USA
| | - David A. Kring
- Center for Lunar Science and Exploration, Lunar and Planetary Institute, Universities Space Research Association, 3600 Bay Area Boulevard, Houston, TX 77058, USA
- NASA Lunar Science Institute
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105
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Kupper S, Tornow C, Gast P. Two different sources of water for the early solar nebula. ORIGINS LIFE EVOL B 2012; 42:81-92. [PMID: 22644567 DOI: 10.1007/s11084-012-9280-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2011] [Accepted: 02/08/2012] [Indexed: 10/27/2022]
Abstract
Water is essential for life. This is a trivial fact but has profound implications since the forming of life on the early Earth required water. The sources of water and the related amount of delivery depend not only on the conditions on the early Earth itself but also on the evolutionary history of the solar system. Thus we ask where and when water formed in the solar nebula-the precursor of the solar system. In this paper we explore the chemical mechanics for water formation and its expected abundance. This is achieved by studying the parental cloud core of the solar nebula and its gravitational collapse. We have identified two different sources of water for the region of Earth's accretion. The first being the sublimation of the icy mantles of dust grains formed in the parental cloud. The second source is located in the inner region of the collapsing cloud core - the so-called hot corino with a temperature of several hundred Kelvin. There, water is produced efficiently in the gas phase by reactions between neutral molecules. Additionally, we analyse the dependence of the production of water on the initial abundance ratio between carbon and oxygen.
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Affiliation(s)
- Stefan Kupper
- German Aerospace Center, Institute of Planetary Research, Rutherfordstr. 2, 12489, Berlin, Germany.
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106
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An Archaean heavy bombardment from a destabilized extension of the asteroid belt. Nature 2012; 485:78-81. [PMID: 22535245 DOI: 10.1038/nature10967] [Citation(s) in RCA: 301] [Impact Index Per Article: 25.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2011] [Accepted: 02/17/2012] [Indexed: 11/08/2022]
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107
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108
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Paganini L, Mumma M, Bonev B, Villanueva G, DiSanti M, Keane J, Meech K. The formation heritage of Jupiter Family Comet 10P/Tempel 2 as revealed by infrared spectroscopy. ICARUS 2012; 218:644-653. [PMID: 32675835 PMCID: PMC7365286 DOI: 10.1016/j.icarus.2012.01.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
We present spectral and spatial information for major volatile species in Comet 10P/Tempel 2, based on high-dispersion infrared spectra acquired on UT 2010 July 26 (heliocentric distance R h = 1.44 AU) and September 18 (R h = 1.62 AU), following the comet's perihelion passage on UT 2010 July 04. The total production rate for water on July 26 was (1.90 ± 0.12) × 1028 molecules s-1, and abundances of six trace gases (relative to water) were: CH3OH (1.58% ± 0.23%), C2H6 (0.39% ± 0.04%), NH3 (0.83% ± 0.20%), and HCN (0.13% ± 0.02%). A detailed analysis of intensities for water emission lines provided a rotational temperature of 35 ± 3 K. The mean OPR is consistent with nuclear spin populations in statistical equilibrium (OPR = 3.01 ± 0.18), and the (1σ) lower bound corresponds to a spin temperature >38 K. Our measurements were contemporaneous with a jet-like feature observed at optical wavelengths. The spatial profiles of four primary volatiles display strong enhancements in the jet direction, which favors release from a localized vent on the nucleus. The measured IR continuum is much more sharply peaked and is consistent with a dominant contribution from the nucleus itself. The peak intensities for H2O, CH3OH, and C2H6 are offset by ~200 km in the jet direction, suggesting the possible existence of a distributed source, such as the release of icy grains that subsequently sublimed in the coma. On UT September 18, no obvious emission lines were present in our spectra, nevertheless we obtained a 3σ upper limit Q(H2O) < 2.86 × 1027 molecules s-1.
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Affiliation(s)
- L. Paganini
- Goddard Center for Astrobiology, NASA GSFC, MS 690, Greenbelt, MD 20771, USA
| | - M.J. Mumma
- Goddard Center for Astrobiology, NASA GSFC, MS 690, Greenbelt, MD 20771, USA
| | - B.P. Bonev
- Goddard Center for Astrobiology, NASA GSFC, MS 690, Greenbelt, MD 20771, USA
- Department of Physics, Catholic University of America, Washington, DC 20064, USA
| | - G.L. Villanueva
- Goddard Center for Astrobiology, NASA GSFC, MS 690, Greenbelt, MD 20771, USA
- Department of Physics, Catholic University of America, Washington, DC 20064, USA
| | - M.A. DiSanti
- Goddard Center for Astrobiology, NASA GSFC, MS 690, Greenbelt, MD 20771, USA
| | - J.V. Keane
- Institute for Astronomy, Univ. of Hawaii, Honolulu, HI 96822, USA
| | - K.J. Meech
- Institute for Astronomy, Univ. of Hawaii, Honolulu, HI 96822, USA
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109
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Fassett CI, Head JW, Kadish SJ, Mazarico E, Neumann GA, Smith DE, Zuber MT. Lunar impact basins: Stratigraphy, sequence and ages from superposed impact crater populations measured from Lunar Orbiter Laser Altimeter (LOLA) data. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2011je003951] [Citation(s) in RCA: 88] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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110
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Ferus M, Kubelík P, Civiš S. Laser Spark Formamide Decomposition Studied by FT-IR Spectroscopy. J Phys Chem A 2011; 115:12132-41. [DOI: 10.1021/jp205413d] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- M. Ferus
- J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova 3, 18223 Prague 8, Czech Republic
- Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8, Czech Republic
| | - P. Kubelík
- J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova 3, 18223 Prague 8, Czech Republic
- Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague 8, Czech Republic
| | - S. Civiš
- J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova 3, 18223 Prague 8, Czech Republic
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111
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Hartogh P, Lis DC, Bockelée-Morvan D, de Val-Borro M, Biver N, Küppers M, Emprechtinger M, Bergin EA, Crovisier J, Rengel M, Moreno R, Szutowicz S, Blake GA. Ocean-like water in the Jupiter-family comet 103P/Hartley 2. Nature 2011; 478:218-20. [PMID: 21976024 DOI: 10.1038/nature10519] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2011] [Accepted: 08/30/2011] [Indexed: 11/09/2022]
Abstract
For decades, the source of Earth's volatiles, especially water with a deuterium-to-hydrogen ratio (D/H) of (1.558 ± 0.001) × 10(-4), has been a subject of debate. The similarity of Earth's bulk composition to that of meteorites known as enstatite chondrites suggests a dry proto-Earth with subsequent delivery of volatiles by local accretion or impacts of asteroids or comets. Previous measurements in six comets from the Oort cloud yielded a mean D/H ratio of (2.96 ± 0.25) × 10(-4). The D/H value in carbonaceous chondrites, (1.4 ± 0.1) × 10(-4), together with dynamical simulations, led to models in which asteroids were the main source of Earth's water, with ≤10 per cent being delivered by comets. Here we report that the D/H ratio in the Jupiter-family comet 103P/Hartley 2, which originated in the Kuiper belt, is (1.61 ± 0.24) × 10(-4). This result substantially expands the reservoir of Earth ocean-like water to include some comets, and is consistent with the emerging picture of a complex dynamical evolution of the early Solar System.
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Affiliation(s)
- Paul Hartogh
- Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany.
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112
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Walsh KJ, Morbidelli A, Raymond SN, O'Brien DP, Mandell AM. A low mass for Mars from Jupiter's early gas-driven migration. Nature 2011; 475:206-9. [PMID: 21642961 DOI: 10.1038/nature10201] [Citation(s) in RCA: 861] [Impact Index Per Article: 66.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2010] [Accepted: 04/01/2011] [Indexed: 11/09/2022]
Abstract
Jupiter and Saturn formed in a few million years (ref. 1) from a gas-dominated protoplanetary disk, and were susceptible to gas-driven migration of their orbits on timescales of only ∼100,000 years (ref. 2). Hydrodynamic simulations show that these giant planets can undergo a two-stage, inward-then-outward, migration. The terrestrial planets finished accreting much later, and their characteristics, including Mars' small mass, are best reproduced by starting from a planetesimal disk with an outer edge at about one astronomical unit from the Sun (1 au is the Earth-Sun distance). Here we report simulations of the early Solar System that show how the inward migration of Jupiter to 1.5 au, and its subsequent outward migration, lead to a planetesimal disk truncated at 1 au; the terrestrial planets then form from this disk over the next 30-50 million years, with an Earth/Mars mass ratio consistent with observations. Scattering by Jupiter initially empties but then repopulates the asteroid belt, with inner-belt bodies originating between 1 and 3 au and outer-belt bodies originating between and beyond the giant planets. This explains the significant compositional differences across the asteroid belt. The key aspect missing from previous models of terrestrial planet formation is the substantial radial migration of the giant planets, which suggests that their behaviour is more similar to that inferred for extrasolar planets than previously thought.
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Affiliation(s)
- Kevin J Walsh
- 1] Université de Nice - Sophia Antipolis, CNRS, Observatoire de la Côte d'Azur, BP 4229, 06304 Nice Cedex 4, France.
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113
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Andrews-Hanna JC, Lewis KW. Early Mars hydrology: 2. Hydrological evolution in the Noachian and Hesperian epochs. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2010je003709] [Citation(s) in RCA: 94] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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114
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Ehrenfreund P, Spaans M, Holm NG. The evolution of organic matter in space. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2011; 369:538-554. [PMID: 21220279 DOI: 10.1098/rsta.2010.0231] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Carbon, and molecules made from it, have already been observed in the early Universe. During cosmic time, many galaxies undergo intense periods of star formation, during which heavy elements like carbon, oxygen, nitrogen, silicon and iron are produced. Also, many complex molecules, from carbon monoxide to polycyclic aromatic hydrocarbons, are detected in these systems, like they are for our own Galaxy. Interstellar molecular clouds and circumstellar envelopes are factories of complex molecular synthesis. A surprisingly high number of molecules that are used in contemporary biochemistry on the Earth are found in the interstellar medium, planetary atmospheres and surfaces, comets, asteroids and meteorites and interplanetary dust particles. Large quantities of extra-terrestrial material were delivered via comets and asteroids to young planetary surfaces during the heavy bombardment phase. Monitoring the formation and evolution of organic matter in space is crucial in order to determine the prebiotic reservoirs available to the early Earth. It is equally important to reveal abiotic routes to prebiotic molecules in the Earth environments. Materials from both carbon sources (extra-terrestrial and endogenous) may have contributed to biochemical pathways on the Earth leading to life's origin. The research avenues discussed also guide us to extend our knowledge to other habitable worlds.
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Affiliation(s)
- Pascale Ehrenfreund
- Space Policy Institute, 1957 E Street, Suite 403, Washington, DC 20052, USA.
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115
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Cirković MM, Sandberg A, Bostrom N. Anthropic shadow: observation selection effects and human extinction risks. RISK ANALYSIS : AN OFFICIAL PUBLICATION OF THE SOCIETY FOR RISK ANALYSIS 2010; 30:1495-1506. [PMID: 20626690 DOI: 10.1111/j.1539-6924.2010.01460.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
We describe a significant practical consequence of taking anthropic biases into account in deriving predictions for rare stochastic catastrophic events. The risks associated with catastrophes such as asteroidal/cometary impacts, supervolcanic episodes, and explosions of supernovae/gamma-ray bursts are based on their observed frequencies. As a result, the frequencies of catastrophes that destroy or are otherwise incompatible with the existence of observers are systematically underestimated. We describe the consequences of this anthropic bias for estimation of catastrophic risks, and suggest some directions for future work.
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116
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Ehrenfreund P, Cami J. Cosmic carbon chemistry: from the interstellar medium to the early Earth. Cold Spring Harb Perspect Biol 2010; 2:a002097. [PMID: 20554702 DOI: 10.1101/cshperspect.a002097] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Astronomical observations have shown that carbonaceous compounds in the gas and solid state, refractory and icy are ubiquitous in our and distant galaxies. Interstellar molecular clouds and circumstellar envelopes are factories of complex molecular synthesis. A surprisingly large number of molecules that are used in contemporary biochemistry on Earth are found in the interstellar medium, planetary atmospheres and surfaces, comets, asteroids and meteorites, and interplanetary dust particles. In this article we review the current knowledge of abundant organic material in different space environments and investigate the connection between presolar and solar system material, based on observations of interstellar dust and gas, cometary volatiles, simulation experiments, and the analysis of extraterrestrial matter. Current challenges in astrochemistry are discussed and future research directions are proposed.
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117
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Fournier GP, Huang J, Gogarten JP. Horizontal gene transfer from extinct and extant lineages: biological innovation and the coral of life. Philos Trans R Soc Lond B Biol Sci 2009; 364:2229-39. [PMID: 19571243 PMCID: PMC2873001 DOI: 10.1098/rstb.2009.0033] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Horizontal gene transfer (HGT) is often considered to be a source of error in phylogenetic reconstruction, causing individual gene trees within an organismal lineage to be incongruent, obfuscating the 'true' evolutionary history. However, when identified as such, HGTs between divergent organismal lineages are useful, phylogenetically informative characters that can provide insight into evolutionary history. Here, we discuss several distinct HGT events involving all three domains of life, illustrating the selective advantages that can be conveyed via HGT, and the utility of HGT in aiding phylogenetic reconstruction and in dating the relative sequence of speciation events. We also discuss the role of HGT from extinct lineages, and its impact on our understanding of the evolution of life on Earth. Organismal phylogeny needs to incorporate reticulations; a simple tree does not provide an accurate depiction of the processes that have shaped life's history.
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Affiliation(s)
- Gregory P. Fournier
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269-31258, USA
| | - Jinling Huang
- Department of Biology, East Carolina University, Greenville, NC 27858, USA
| | - J. Peter Gogarten
- Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT 06269-31258, USA
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118
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Abstract
We present numerical simulations to model the production of observable long-period comets (LPCs) from the Oort Cloud, a vast reservoir of icy bodies surrounding the Sun. We show that inner Oort Cloud objects can penetrate Jupiter's orbit via a largely unexplored dynamical pathway, and they are an important, if not the dominant, source of known LPCs. We use this LPC production to place observationally motivated constraints on the population and mass of the inner Oort Cloud, which are consistent with giant planet formation theory. These constraints indicate that only one comet shower producing late Eocene bombardment levels has likely occurred since the Cambrian Explosion, making these phenomena an improbable cause of additional extinction events.
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Affiliation(s)
- Nathan A Kaib
- Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195-1580, USA.
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119
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Microbial habitability of the Hadean Earth during the late heavy bombardment. Nature 2009; 459:419-22. [PMID: 19458721 DOI: 10.1038/nature08015] [Citation(s) in RCA: 210] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2008] [Accepted: 03/24/2009] [Indexed: 11/08/2022]
Abstract
Lunar rocks and impact melts, lunar and asteroidal meteorites, and an ancient martian meteorite record thermal metamorphic events with ages that group around and/or do not exceed 3.9 Gyr. That such a diverse suite of solar system materials share this feature is interpreted to be the result of a post-primary-accretion cataclysmic spike in the number of impacts commonly referred to as the late heavy bombardment (LHB). Despite its obvious significance to the preservation of crust and the survivability of an emergent biosphere, the thermal effects of this bombardment on the young Earth remain poorly constrained. Here we report numerical models constructed to probe the degree of thermal metamorphism in the crust in the effort to recreate the effect of the LHB on the Earth as a whole; outputs were used to assess habitable volumes of crust for a possible near-surface and subsurface primordial microbial biosphere. Our analysis shows that there is no plausible situation in which the habitable zone was fully sterilized on Earth, at least since the termination of primary accretion of the planets and the postulated impact origin of the Moon. Our results explain the root location of hyperthermophilic bacteria in the phylogenetic tree for 16S small-subunit ribosomal RNA, and bode well for the persistence of microbial biospheres even on planetary bodies strongly reworked by impacts.
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120
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Levison HF, Bottke WF, Gounelle M, Morbidelli A, Nesvorný D, Tsiganis K. Contamination of the asteroid belt by primordial trans-Neptunian objects. Nature 2009; 460:364-6. [DOI: 10.1038/nature08094] [Citation(s) in RCA: 220] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2009] [Accepted: 04/24/2009] [Indexed: 11/09/2022]
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121
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Pristine extraterrestrial material with unprecedented nitrogen isotopic variation. Proc Natl Acad Sci U S A 2009; 106:10522-7. [PMID: 19528640 DOI: 10.1073/pnas.0901546106] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Pristine meteoritic materials carry light element isotopic fractionations that constrain physiochemical conditions during solar system formation. Here we report the discovery of a unique xenolith in the metal-rich chondrite Isheyevo. Its fine-grained, highly pristine mineralogy has similarity with interplanetary dust particles (IDPs), but the volume of the xenolith is more than 30,000 times that of a typical IDP. Furthermore, an extreme continuum of N isotopic variation is present in this xenolith: from very light N isotopic composition (delta(15)N(AIR) = -310 +/- 20 per thousand), similar to that inferred for the solar nebula, to the heaviest ratios measured in any solar system material (delta(15)N(AIR) = 4,900 +/- 300 per thousand). At the same time, its hydrogen and carbon isotopic compositions exhibit very little variation. This object poses serious challenges for existing models for the origin of light element isotopic anomalies.
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122
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Roberts JH, Lillis RJ, Manga M. Giant impacts on early Mars and the cessation of the Martian dynamo. ACTA ACUST UNITED AC 2009. [DOI: 10.1029/2008je003287] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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123
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On the free energy that drove primordial anabolism. Int J Mol Sci 2009; 10:1853-1871. [PMID: 19468343 PMCID: PMC2680651 DOI: 10.3390/ijms10041853] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2009] [Revised: 04/16/2009] [Accepted: 04/20/2009] [Indexed: 12/25/2022] Open
Abstract
A key problem in understanding the origin of life is to explain the mechanism(s) that led to the spontaneous assembly of molecular building blocks that ultimately resulted in the appearance of macromolecular structures as they are known in modern biochemistry today. An indispensable thermodynamic prerequisite for such a primordial anabolism is the mechanistic coupling to processes that supplied the free energy required. Here I review different sources of free energy and discuss the potential of each form having been involved in the very first anabolic reactions that were fundamental to increase molecular complexity and thus were essential for life.
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124
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Minton DA, Malhotra R. A record of planet migration in the main asteroid belt. Nature 2009; 457:1109-11. [DOI: 10.1038/nature07778] [Citation(s) in RCA: 133] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2008] [Accepted: 01/13/2009] [Indexed: 11/09/2022]
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125
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Pham LBS, Karatekin O, Dehant V. Effects of meteorite impacts on the atmospheric evolution of Mars. ASTROBIOLOGY 2009; 9:45-54. [PMID: 19317624 DOI: 10.1089/ast.2008.0242] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Early in its history, Mars probably had a denser atmosphere with sufficient greenhouse gases to sustain the presence of stable liquid water at the surface. Impacts by asteroids and comets would have played a significant role in the evolution of the martian atmosphere, not only by causing atmospheric erosion but also by delivering material and volatiles to the planet. We investigate the atmospheric loss and the delivery of volatiles with an analytical model that takes into account the impact simulation results and the flux of impactors given in the literature. The atmospheric loss and the delivery of volatiles are calculated to obtain the atmospheric pressure evolution. Our results suggest that the impacts alone cannot satisfactorily explain the loss of significant atmospheric mass since the Late Noachian (approximately 3.7-4 Ga). A period with intense bombardment of meteorites could have increased the atmospheric loss; but to explain the loss of a speculative massive atmosphere in the Late Noachian, other factors of atmospheric erosion and replenishment also need to be taken into account.
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126
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Leblanc F, Langlais B, Fouchet T, Barabash S, Breuer D, Chassefière E, Coates A, Dehant V, Forget F, Lammer H, Lewis S, Lopez-Valverde M, Mandea M, Menvielle M, Pais A, Paetzold M, Read P, Sotin C, Tarits P, Vennerstrom S. Mars environment and magnetic orbiter scientific and measurement objectives. ASTROBIOLOGY 2009; 9:71-89. [PMID: 19317625 DOI: 10.1089/ast.2007.0222] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
In this paper, we summarize our present understanding of Mars' atmosphere, magnetic field, and surface and address past evolution of these features. Key scientific questions concerning Mars' surface, atmosphere, and magnetic field, along with the planet's interaction with solar wind, are discussed. We also define what key parameters and measurements should be performed and the main characteristics of a martian mission that would help to provide answers to these questions. Such a mission--Mars Environment and Magnetic Orbiter (MEMO)--was proposed as an answer to the Cosmic Vision Call of Opportunity as an M-class mission (corresponding to a total European Space Agency cost of less than 300 Meuro). MEMO was designed to study the strong interconnection between the planetary interior, atmosphere, and solar conditions, which is essential to our understanding of planetary evolution, the appearance of life, and its sustainability. The MEMO main platform combined remote sensing and in situ measurements of the atmosphere and the magnetic field during regular incursions into the martian upper atmosphere. The micro-satellite was designed to perform simultaneous in situ solar wind measurements. MEMO was defined to conduct: * Four-dimensional mapping of the martian atmosphere from the surface up to 120 km by measuring wind, temperature, water, and composition, all of which would provide a complete view of the martian climate and photochemical system; Mapping of the low-altitude magnetic field with unprecedented geographical, altitude, local time, and seasonal resolutions; A characterization of the simultaneous responses of the atmosphere, magnetic field, and near-Mars space to solar variability by means of in situ atmospheric and solar wind measurements.
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Affiliation(s)
- F Leblanc
- Service d'Aéronomie du CNRS/IPSL, Université Pierre et Marie Curie, France.
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127
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Boussau B, Blanquart S, Necsulea A, Lartillot N, Gouy M. Parallel adaptations to high temperatures in the Archaean eon. Nature 2008; 456:942-5. [DOI: 10.1038/nature07393] [Citation(s) in RCA: 173] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2008] [Accepted: 09/01/2008] [Indexed: 11/09/2022]
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Strom RG, Chapman CR, Merline WJ, Solomon SC, Head JW. Mercury Cratering Record Viewed from MESSENGER's First Flyby. Science 2008; 321:79-81. [DOI: 10.1126/science.1159317] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- Robert G. Strom
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA
- Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80302, USA
- Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015, USA
- Department of Geological Sciences, Brown University, Providence, RI 02912, USA
| | - Clark R. Chapman
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA
- Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80302, USA
- Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015, USA
- Department of Geological Sciences, Brown University, Providence, RI 02912, USA
| | - William J. Merline
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA
- Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80302, USA
- Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015, USA
- Department of Geological Sciences, Brown University, Providence, RI 02912, USA
| | - Sean C. Solomon
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA
- Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80302, USA
- Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015, USA
- Department of Geological Sciences, Brown University, Providence, RI 02912, USA
| | - James W. Head
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA
- Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80302, USA
- Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015, USA
- Department of Geological Sciences, Brown University, Providence, RI 02912, USA
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129
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130
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Gronstal A, Cockell CS, Perino MA, Bittner T, Clacey E, Clark O, Ingold O, Alves de Oliveira C, Wathiong S. Lunar astrobiology: a review and suggested laboratory equipment. ASTROBIOLOGY 2007; 7:767-782. [PMID: 17963476 DOI: 10.1089/ast.2006.0082] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
In October of 2005, the European Space Agency (ESA) and Alcatel Alenia Spazio released a "call to academia for innovative concepts and technologies for lunar exploration." In recent years, interest in lunar exploration has increased in numerous space programs around the globe, and the purpose of our study, in response to the ESA call, was to draw on the expertise of researchers and university students to examine science questions and technologies that could support human astrobiology activity on the Moon. In this mini review, we discuss astrobiology science questions of importance for a human presence on the surface of the Moon and we provide a summary of key instrumentation requirements to support a lunar astrobiology laboratory.
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Affiliation(s)
- Aaron Gronstal
- Planetary and Space Sciences Research Institute, Open University, Milton Keynes, United Kingdom.
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131
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Chaufray JY, Modolo R, Leblanc F, Chanteur G, Johnson RE, Luhmann JG. Mars solar wind interaction: Formation of the Martian corona and atmospheric loss to space. ACTA ACUST UNITED AC 2007. [DOI: 10.1029/2007je002915] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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132
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133
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Forterre P, Gribaldo S. The origin of modern terrestrial life. HFSP JOURNAL 2007; 1:156-68. [PMID: 19404443 PMCID: PMC2640990 DOI: 10.2976/1.2759103] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/22/2007] [Accepted: 06/22/2007] [Indexed: 11/19/2022]
Abstract
The study of the origin of life covers many areas of expertise and requires the input of various scientific communities. In recent years, this research field has often been viewed as part of a broader agenda under the name of "exobiology" or "astrobiology." In this review, we have somewhat narrowed this agenda, focusing on the origin of modern terrestrial life. The adjective "modern" here means that we did not speculate on different forms of life that could have possibly appeared on our planet, but instead focus on the existing forms (cells and viruses). We try to briefly present the state of the art about alternative hypotheses discussing not only the origin of life per se, but also how life evolved to produce the modern biosphere through a succession of steps that we would like to characterize as much as possible.
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Affiliation(s)
- Patrick Forterre
- Institut Pasteur, 25 rue du Docteur Roux,
75015 Paris et Université Paris-Sud, CNRS, UMR 8621, 91405, Crsay-Cedex,
France
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134
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Raymond SN, Quinn T, Lunine JI. High-resolution simulations of the final assembly of Earth-like planets. 2. Water delivery and planetary habitability. ASTROBIOLOGY 2007; 7:66-84. [PMID: 17407404 DOI: 10.1089/ast.2006.06-0126] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
The water content and habitability of terrestrial planets are determined during their final assembly, from perhaps 100 1,000-km "planetary embryos " and a swarm of billions of 1-10-km "planetesimals. " During this process, we assume that water-rich material is accreted by terrestrial planets via impacts of water-rich bodies that originate in the outer asteroid region. We present analysis of water delivery and planetary habitability in five high-resolution simulations containing about 10 times more particles than in previous simulations. These simulations formed 15 terrestrial planets from 0.4 to 2.6 Earth masses, including five planets in the habitable zone. Every planet from each simulation accreted at least the Earth's current water budget; most accreted several times that amount (assuming no impact depletion). Each planet accreted at least five water-rich embryos and planetesimals from the past 2.5 astronomical units; most accreted 10-20 water-rich bodies. We present a new model for water delivery to terrestrial planets in dynamically calm systems, with low-eccentricity or low-mass giant planets-such systems may be very common in the Galaxy. We suggest that water is accreted in comparable amounts from a few planetary embryos in a " hit or miss " way and from millions of planetesimals in a statistically robust process. Variations in water content are likely to be caused by fluctuations in the number of water-rich embryos accreted, as well as from systematic effects, such as planetary mass and location, and giant planet properties.
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Affiliation(s)
- Sean N Raymond
- NASA Postdoctoral Program Fellow, Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, Colorado 80309-0389, USA.
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135
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Abstract
The development of prebiotic homochirality on early-Earth or another planetary platform may be viewed as a critical phenomenon. It is shown, in the context of spatio-temporal polymerization reaction networks, that environmental effects--be they temperature surges or other external disruptions--may destroy any net chirality previously produced. In order to understand the emergence of prebiotic homochirality it is important to model the coupling of polymerization reaction networks to different planetary environments.
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Affiliation(s)
- Marcelo Gleiser
- Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755, USA.
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136
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Ferris JP. Montmorillonite-catalysed formation of RNA oligomers: the possible role of catalysis in the origins of life. Philos Trans R Soc Lond B Biol Sci 2006; 361:1777-86; discussion 1786. [PMID: 17008218 PMCID: PMC1664692 DOI: 10.1098/rstb.2006.1903] [Citation(s) in RCA: 112] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Large deposits of montmorillonite are present on the Earth today and it is believed to have been present at the time of the origin of life and has recently been detected on Mars. It is formed by aqueous weathering of volcanic ash. It catalyses the formation of oligomers of RNA that contain monomer units from 2 to 30-50. Oligomers of this length are formed because this catalyst controls the structure of the oligomers formed and does not generate all possible isomers. Evidence of sequence-, regio- and homochiral selectivity in these oligomers has been obtained. Postulates on the role of selective versus specific catalysts on the origins of life are discussed. An introduction to the origin of life is given with an emphasis on reaction conditions based on the recent data obtained from zircons 4.0-4.5Ga.
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Affiliation(s)
- James P Ferris
- Department of Chemistry and Chemical Biology and the New York Centre for Studies on the Origins of Life, Rensselaer Polytechnic Institute, Troy, NY 12180, USA.
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137
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Billings L, Cameron V, Claire M, Dick GJ, Domagal-Goldman SD, Javaux EJ, Johnson OJ, Laws C, Race MS, Rask J, Rummel JD, Schelble RT, Vance S. The astrobiology primer: an outline of general knowledge--version 1, 2006. ASTROBIOLOGY 2006; 6:735-813. [PMID: 17067259 DOI: 10.1089/ast.2006.6.735] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
The Astrobiology Primer has been created as a reference tool for those who are interested in the interdisciplinary field of astrobiology. The field incorporates many diverse research endeavors, but it is our hope that this slim volume will present the reader with all he or she needs to know to become involved and to understand, at least at a fundamental level, the state of the art. Each section includes a brief overview of a topic and a short list of readable and important literature for those interested in deeper knowledge. Because of the great diversity of material, each section was written by a different author with a different expertise. Contributors, authors, and editors are listed at the beginning, along with a list of those chapters and sections for which they were responsible. We are deeply indebted to the NASA Astrobiology Institute (NAI), in particular to Estelle Dodson, David Morrison, Ed Goolish, Krisstina Wilmoth, and Rose Grymes for their continued enthusiasm and support. The Primer came about in large part because of NAI support for graduate student research, collaboration, and inclusion as well as direct funding. We have entitled the Primer version 1 in hope that it will be only the first in a series, whose future volumes will be produced every 3-5 years. This way we can insure that the Primer keeps up with the current state of research. We hope that it will be a great resource for anyone trying to stay abreast of an ever-changing field.
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138
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Brunini A. Origin of the obliquities of the giant planets in mutual interactions in the early Solar System. Nature 2006; 440:1163-5. [PMID: 16641989 DOI: 10.1038/nature04577] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2005] [Accepted: 01/02/2006] [Indexed: 11/09/2022]
Abstract
The origin of the spin-axis orientations (obliquities) of the giant planets is a fundamental issue because if the obliquities resulted from tangential collisions with primordial Earth-sized protoplanets, then they are related to the masses of the largest planetesimals out of which the planets form. A problem with this mechanism, however, is that the orbital planes of regular satellites would probably be uncorrelated with the obliquities, contrary to observations. Alternatively, they could have come from an external twist that affected the orientation of the Solar System plane; but in this model, the outer planets must have formed too rapidly, before the event that produced the twist. Moreover, the model cannot be quantitatively tested. Here I show that the present obliquities of the giant planets were probably achieved when Jupiter and Saturn crossed the 1:2 orbital resonance during a specific migration process: different migration scenarios cannot account for the large observed obliquities. The existence of the regular satellites of the giant planets does not represent a problem in this model because, although they formed soon after the planetary formation, they can follow the slow evolution of the equatorial plane it produces.
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Affiliation(s)
- Adrián Brunini
- Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque s/n (1900) La Plata, Argentina.
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139
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140
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Affiliation(s)
- Alan Fitzsimmons
- Astrophysics Research Center, School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN, Northern Ireland, UK.
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141
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Bottke WF, Nesvorný D, Grimm RE, Morbidelli A, O'Brien DP. Iron meteorites as remnants of planetesimals formed in the terrestrial planet region. Nature 2006; 439:821-4. [PMID: 16482151 DOI: 10.1038/nature04536] [Citation(s) in RCA: 219] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2005] [Accepted: 12/12/2005] [Indexed: 11/09/2022]
Abstract
Iron meteorites are core fragments from differentiated and subsequently disrupted planetesimals. The parent bodies are usually assumed to have formed in the main asteroid belt, which is the source of most meteorites. Observational evidence, however, does not indicate that differentiated bodies or their fragments were ever common there. This view is also difficult to reconcile with the fact that the parent bodies of iron meteorites were as small as 20 km in diameter and that they formed 1-2 Myr earlier than the parent bodies of the ordinary chondrites. Here we show that the iron-meteorite parent bodies most probably formed in the terrestrial planet region. Fast accretion times there allowed small planetesimals to melt early in Solar System history by the decay of short-lived radionuclides (such as 26Al, 60Fe). The protoplanets emerging from this population not only induced collisional evolution among the remaining planetesimals but also scattered some of the survivors into the main belt, where they stayed for billions of years before escaping via a combination of collisions, Yarkovsky thermal forces, and resonances. We predict that some asteroids are main-belt interlopers (such as (4) Vesta). A select few may even be remnants of the long-lost precursor material that formed the Earth.
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Affiliation(s)
- William F Bottke
- Southwest Research Institute, 1050 Walnut St, Suite 400, Boulder, Colorado 80302, USA.
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142
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Strom RG, Malhotra R, Ito T, Yoshida F, Kring DA. The origin of planetary impactors in the inner solar system. Science 2005; 309:1847-50. [PMID: 16166515 DOI: 10.1126/science.1113544] [Citation(s) in RCA: 346] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Insights into the history of the inner solar system can be derived from the impact cratering record of the Moon, Mars, Venus, and Mercury and from the size distributions of asteroid populations. Old craters from a unique period of heavy bombardment that ended approximately 3.8 billion years ago were made by asteroids that were dynamically ejected from the main asteroid belt, possibly due to the orbital migration of the giant planets. The impactors of the past approximately 3.8 billion years have a size distribution quite different from that of the main belt asteroids but very similar to that of near-Earth asteroids.
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Affiliation(s)
- Robert G Strom
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA
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143
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Morbidelli A, Levison HF, Tsiganis K, Gomes R. Chaotic capture of Jupiter's Trojan asteroids in the early Solar System. Nature 2005; 435:462-5. [PMID: 15917801 DOI: 10.1038/nature03540] [Citation(s) in RCA: 639] [Impact Index Per Article: 33.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2004] [Accepted: 03/11/2005] [Indexed: 11/09/2022]
Abstract
Jupiter's Trojans are asteroids that follow essentially the same orbit as Jupiter, but lead or trail the planet by an angular distance of approximately 60 degrees (co-orbital motion). They are hypothesized to be planetesimals that formed near Jupiter and were captured onto their current orbits while Jupiter was growing, possibly with the help of gas drag and/or collisions. This idea, however, cannot explain some basic properties of the Trojan population, in particular its broad orbital inclination distribution, which ranges up to approximately 40 degrees (ref. 8). Here we show that the Trojans could have formed in more distant regions and been subsequently captured into co-orbital motion with Jupiter during the time when the giant planets migrated by removing neighbouring planetesimals. The capture was possible during a short period of time, just after Jupiter and Saturn crossed their mutual 1:2 resonance, when the dynamics of the Trojan region were completely chaotic. Our simulations of this process satisfactorily reproduce the orbital distribution of the Trojans and their total mass.
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Affiliation(s)
- A Morbidelli
- Observatoire de la Côte d'Azur, BP 4229, 06304 Nice Cedex 4, France
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144
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145
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Tsiganis K, Gomes R, Morbidelli A, Levison HF. Origin of the orbital architecture of the giant planets of the Solar System. Nature 2005; 435:459-61. [PMID: 15917800 DOI: 10.1038/nature03539] [Citation(s) in RCA: 998] [Impact Index Per Article: 52.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2004] [Accepted: 03/11/2005] [Indexed: 11/09/2022]
Abstract
Planetary formation theories suggest that the giant planets formed on circular and coplanar orbits. The eccentricities of Jupiter, Saturn and Uranus, however, reach values of 6 per cent, 9 per cent and 8 per cent, respectively. In addition, the inclinations of the orbital planes of Saturn, Uranus and Neptune take maximum values of approximately 2 degrees with respect to the mean orbital plane of Jupiter. Existing models for the excitation of the eccentricity of extrasolar giant planets have not been successfully applied to the Solar System. Here we show that a planetary system with initial quasi-circular, coplanar orbits would have evolved to the current orbital configuration, provided that Jupiter and Saturn crossed their 1:2 orbital resonance. We show that this resonance crossing could have occurred as the giant planets migrated owing to their interaction with a disk of planetesimals. Our model reproduces all the important characteristics of the giant planets' orbits, namely their final semimajor axes, eccentricities and mutual inclinations.
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Affiliation(s)
- K Tsiganis
- Observatoire de la Côte d' Azur, CNRS, BP 4229, 06304 Nice Cedex 4, France
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146
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Schulze-Makuch D, Irwin LN, Lipps JH, LeMone D, Dohm JM, Fairén AG. Scenarios for the evolution of life on Mars. ACTA ACUST UNITED AC 2005. [DOI: 10.1029/2005je002430] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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