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At least 73 records · Page 4Linked to original sources
PubMed2000

The ascent of parity-violation: exochirality in the solar system and beyond

We review recent developments stemming from Stephen Mason's work on the origin of homochirality, focusing in particular on the parity-violating energy difference (PVED) between enantiomers. We summarize results of calculations of the PVED--both our own and those of other groups--which show that the natural enantiomers are indeed favoured by the weak force in most cases. The PVED has become important not only to explain the selection of the L-amino acids in the origin of life, but also as a "molecular footprint" of fundamental physics, leading to proposals to derive values of the Weinberg angle from future spectroscopic measurements of the PVED. The new field of exochirality--chirality outside the Earth--is now taking off, with reports of excesses of L-amino acids in meteorites, and proposals to look for homochirality as a signature of life on other planets and even in other solar systems. If it was indeed the PVED that determined life's handedness, we would expect to find L-amino acids rather than D everywhere in the universe.

Journal Article↗
PubMed2004

Stellar encounters as the origin of distant Solar System objects in highly eccentric orbits.

The Kuiper belt extends from the orbit of Neptune at 30 au to an abrupt outer edge about 50 au from the Sun. Beyond the edge is a sparse population of objects with large orbital eccentricities. Neptune shapes the dynamics of most Kuiper belt objects, but the recently discovered planet 2003 VB12 (Sedna) has an eccentric orbit with a perihelion distance of 70 au, far beyond Neptune's gravitational influence. Although influences from passing stars could have created the Kuiper belt's outer edge and could have scattered objects into large, eccentric orbits, no model currently explains the properties of Sedna. Here we show that a passing star probably scattered Sedna from the Kuiper belt into its observed orbit. The likelihood that a planet at 60-80 au can be scattered into Sedna's orbit is about 50 per cent; this estimate depends critically on the geometry of the fly-by. Even more interesting is the approximately 10 per cent chance that Sedna was captured from the outer disk of the passing star. Most captures have very high inclination orbits; detection of such objects would confirm the presence of extrasolar planets in our own Solar System.

Journal Article↗
PubMed2003

An alternative approach to solar system exploration providing safety of human mission to Mars.

For systematic human Mars exploration, meeting crew safety requirements, it seems perspective to assemble into a spacecraft: an electrical rocket, a well-shielded long-term life support system, and a manipulator-robots operating in combined "presence effect" and "master-slave" mode. The electrical spacecraft would carry humans to the orbit of Mars, providing short distance (and low signal time delay) between operator and robot-manipulators, which are landed on the surface of the planet. Long-term hybrid biological and physical/chemical LSS could provide environment supporting human health and well being. Robot-manipulators operating in "presence effect" and "master-slave" mode exclude necessity of human landing on Martian surface decreasing the level of risk for crew. Since crewmen would not have direct contact with the Martian environment then the problem of mutual biological protection is essentially reduced. Lightweight robot-manipulators, without heavy life support systems and without the necessity of returning to the mother vessel, could be sent as scouts to different places on the planet surface, scanning the most interesting for exobiological research site. Some approximate estimations of electric spacecraft, long-term hybrid LSS, radiation protection and mission parameters are conducted and discussed.

Electricity↗
PubMed2004

Molecular cloud origin for the oxygen isotope heterogeneity in the solar system.

Meteorites and their components have anomalous oxygen isotopic compositions characterized by large variations in 18O/16O and 17O/16O ratios. On the basis of recent observations of star-forming regions and models of accreting protoplanetary disks, we suggest that these variations may originate in a parent molecular cloud by ultraviolet photodissociation processes. Materials with anomalous isotopic compositions were then transported into the solar nebula by icy dust grains during the collapse of the cloud. The icy dust grains drifted toward the Sun in the disk, and their subsequent evaporation resulted in the 17O- and 18O-enrichment of the inner disk gas.

Carbon Isotopes↗
PubMed1988

Estimation of the reaction rate for the formation of CH3O from H + H2CO: implications for chemistry in the Solar System.

It is argued that the formation of the methoxy radical (CH3O) from H + H2CO may play an essential role in the reduction of CO to CH4. The rate coefficient for this reaction has been estimated using the approximate theory of J. Troe (1977a, J. Chem. Phys. 66, 4745) and transition state theory. We briefly discuss the implications of this reaction for the chemistry of CO on Jupiter, in the solar nebula, for interpreting the laboratory experiments of A. Bar-Nun and A. Shaviv (1975, Icarus 24, 197) and A. Bar-Nun and S. Chang (1983, J. Geophys. Res. 88, 6662) and for organic synthesis in the prebiotic terrestrial atmosphere.

Atmosphere↗
PubMed1996

The inventory of interstellar materials available for the formation of the solar system.

Tremendous progress has been made in the field of interstellar dust in recent years through the use of telescopic observations, theoretical studies, laboratory studies of analogs, and the study of actual interstellar samples found in meteorites. It is increasingly clear that the interstellar medium (ISM) contains an enormous diversity of materials created by a wide range of chemical and physical processes. This understanding is a far cry from the picture of interstellar materials held as recently as two decades ago, a picture which incorporated only a few generic types of grains and few molecules. In this paper, I attempt to review some of our current knowledge of the more abundant materials thought to exist in the ISM. The review concentrates on matter in interstellar dense molecular clouds since it is the materials in these environments from which new stars and planetary systems are formed. However, some discussion is reserved for materials in circumstellar environments and in the diffuse ISM. The paper also focuses largely on solid materials as opposed to gases since solids contain a major fraction of the heavier elements in clouds and because solids are most likely to survive incorporation into new planetary systems in identifiable form. The paper concludes with a discussion of some of the implications resulting from the recent growth of our knowledge about interstellar materials and also considers a number of areas in which future work might be expected to yield important results.

Astronomy↗
PubMed2004

The relative transit time of high-rigidity and low-rigidity cosmic rays through the solar system.

A study of neutron monitor count rates with vertical cut-off rigidities from 0.6 to 13 GV indicates that high-energy and low-energy galactic cosmic rays arrive at earth orbit with small time differences compared to a month. This is in contradiction to the theory of the deceleration potential which states that cosmic-ray particles with rigidities greater than 36 V arrive at earth orbit about three months before cosmic-ray particles with lesses rigidines.

Cosmic Radiation↗
PubMed1997

From the interstellar clouds, through the inner to the outer solar system: a universally distributed complex organic chemistry. Preface.

High molecular weight organic compounds are involved in the chemistry and physics of many astrophysical and planetary objects. They are or should be present in interstellar dust, in comets and meteorites, in the Giant planets and Titan, in asteroids Triton and icy satellites. They represent a class of very complex organic material, part of which may have played a role in the origin of life on Earth. Thus they directly concern prebiotic chemistry and exobiology.

Cosmic Dust↗
PubMed1995

Origins of amino acids in the early solar system.

Synthesis of meteoritic amino acids probably took place in the aqueous sub-surface regions of one or more asteroid-sized parent bodies. Starting material for those reactions apparently consisted of a population of more simple compounds including a suite of aliphatic precursors characterised by (1) complete structural diversity, (2) prevalence of branched- over straight-chain species, (3) exponential decrease in abundance with increasing C number, (4) large enrichment in D, and, probably, (5) systematic decrease in 13C/12C with increasing C number. Those properties were apparently acquired during synthesis of the precursors by ion-molecule reactions in a presolar molecular cloud.

Amino Acids↗