Supernovae and the chirality of the amino acids

Neutrinos from Type Ia and Failed Core-Collapse Supernovae at Dark Matter Detectors

Neutrinos produced in the hot and dense interior of the next galactic supernova would be visible at dark matter experiments in coherent elastic nuclear recoils. While studies on this channel have focused on successful core-collapse supernovae, a thermonuclear (type Ia) explosion, or a core collapse that fails to explode and forms a black hole, are as likely to occur as the next galactic supernova event. I show that generation-3 noble liquid-based dark matter experiments such as darwin and argo, operating at sub-keV thresholds with ionization-only signals, would distinguish between (a) leading hypotheses of type Ia explosion mechanisms by detecting an O(1)  s burst of O(1)  MeV neutrinos, and (b) progenitor models of failed supernovae by detecting an O(1)  s burst of O(10)  MeV neutrinos, especially by marking the instant of black hole formation from abrupt stoppage of neutrino detection. This detection is sensitive to all neutrino flavors and insensitive to neutrino oscillations, thereby making measurements complementary to neutrino experiments.

Origin of Terrestrial Bioorganic Homochirality and Symmetry Breaking in the Universe

The origin of terrestrial bioorganic homochirality is one of the most important and unresolved problems in the study of chemical evolution prior to the origin of terrestrial life. One hypothesis advocated in the context of astrobiology is that polarized quantum radiation in space, such as circularly polarized photons or spin-polarized leptons, induced asymmetric chemical and physical conditions in the primitive interstellar media (the cosmic scenario). Another advocated hypothesis in the context of symmetry breaking in the universe is that the bioorganic asymmetry is intrinsically derived from the chiral asymmetric properties of elementary particles, that is, parity violation in the weak interaction (the intrinsic scenario). In this paper, the features of these two scenarios are discussed and approaches to validate them are reviewed.

Homochirality: A Perspective from Fundamental Physics

In this brief review, possible mechanisms which could lead to complete biological homochirality are discussed from the viewpoint of fundamental physics. In particular, the role played by electroweak parity violation, including neutrino-induced homochirality, and contributions from the gravitational interaction, will be emphasized.

Astrophysical Sites that Can Produce Enantiomeric Amino Acids

Recent work has produced theoretical evidence for two sites, colliding neutron stars and neutron-star–Wolf–Rayet binary systems, which might produce amino acids with the left-handed chirality preference found in meteorites. The Supernova Neutrino Amino Acid Processing (SNAAP) model uses electron antineutrinos and the magnetic field from source objects such as neutron stars to preferentially destroy one enantiomer over another. Large enantiomeric excesses are predicted for isovaline and alanine; although based on an earlier study, similar results are expected for the others. Isotopic abundances of 13 C and 15 O in meteorites provide a new test of the SNAAP model. This presents implications for the origins of life.

Biological Homochirality on the Earth, or in the Universe? A Selective Review

The discovery of meteoritic alpha-amino acids with significant enantiomeric excesses of the L-form has suggested that some cosmic factors could serve as the initial source for chiral imbalance of organic compounds delivered to the early Earth. The paper reviews major hypothesis considering the influence of chiral irradiation and chiral combinations of physical fields on the possible ways asymmetric synthesis and transformations of organics could take place within the solar system. They could result in a small enantiomeric imbalance of some groups of compounds. More attention is paid to the hypothesis on parity violation of weak interaction that was supposed to cause homochirality of all primary particles and a more significant homochirality of compounds directly synthesized from the latter in a plasma reactor. The first experiment with material synthesized in a plasma torch resulting from a super-high-velocity impact showed formation of alanine with the excess of L-form between 7 and 25%. The supposed conclusion is that L-amino acids could serve as a starting homochiral biomolecular pool for life to emerge all over the Universe.

Amino Acid Chiral Selection Via Weak Interactions in Stellar Environments: Implications for the Origin of Life

Magnetochiral phenomena may be responsible for the selection of chiral states of biomolecules in meteoric environments. For example, the Supernova Amino Acid Processing (SNAAP) Model was proposed previously as a possible mode of magnetochiral selection of amino acids by way of the weak interaction in strong magnetic fields. In earlier work, this model was shown to produce an enantiomeric excess (ee) as high as 0.014% for alanine. In this paper we present the results of molecular quantum chemistry calculations from which ees are determined for the α-amino acids plus isovaline and norvaline, which were found to have positive ees in meteorites. Calculations are performed for both isolated and aqueous states. In some cases, the aqueous state was found to produce larger ees reaching values as high as a few percent under plausible conditions.

Selection of Amino Acid Chirality via Neutrino Interactions with 14N in Crossed Electric and Magnetic Fields

Previous work has suggested that the chirality of the amino acids could be established in the magnetic field of a nascent neutron star from a core-collapse supernova or massive collapsar. The magnetic field would orient the 14N nuclei, and the alignment of its nuclear spin with respect to those of the electron antineutrinos emitted from the collapsing star would determine the probability of destruction of the 14N nuclei by interactions with the antineutrinos. Subsequent work estimated the bulk polarization of the 14N nuclei in large rotating meteoroids in such an environment. The present work adds a crucial piece of this model by describing the details by which the selective 14N nuclear destruction would produce molecular chiral selectivity. The effects of the neutrino-induced interactions on the 14N nuclei bound in amino acids polarized in strong magnetic fields are studied. It is shown that electric fields in the reference frame of the nuclei modify the magnetic field at the nucleus, creating nuclear magnetizations that are asymmetric in chirality. The antineutrino cross sections depend on this magnetization, creating a selective destructive effect. The environmental conditions and sites in which such a selection mechanism could occur are discussed. Selective destruction of D-enantiomers results in enantiomeric excesses which may be sufficient to drive subsequent autocatalysis necessary to produce the few-percent enantiomeric excesses found in meteorites and subsequent homochirality. Molecular quantum chemical calculations were performed for alanine, and the chirality-dependent effects studied were included. A preference for left-handed molecules was found, and enantiomeric excesses as high as 0.02% were estimated for molecules in the electromagnetic conditions expected from a core-collapse supernova. Key Words: Amino acids-Supernovae-Antineutrinos-Enantiomeric excess-Chirality. Astrobiology 18, 190-206.

A photochemical mechanism for homochirogenesis. Part 2

A theoretical investigation of the photochemistry of racemic compounds with circularly polarized light was undertaken. The exact solutions of the differential equations by numerical integration to the approximate solutions used in an earlier article were compared. The exact solutions showed that sequential reactions yield enhanced optical activities in the products. For irreversible reactions, all enantiomeric excesses are lost if the reactions are carried to completion, but appreciable resolution occurs in many cases for partial conversion. For reversible reactions, significant enantiomeric excesses are found at the photostationary state.

Ionizing radiation and life

Ionizing radiation is a ubiquitous feature of the Cosmos, from exogenous cosmic rays (CR) to the intrinsic mineral radioactivity of a habitable world, and its influences on the emergence and persistence of life are wide-ranging and profound. Much attention has already been focused on the deleterious effects of ionizing radiation on organisms and the complex molecules of life, but ionizing radiation also performs many crucial functions in the generation of habitable planetary environments and the origins of life. This review surveys the role of CR and mineral radioactivity in star formation, generation of biogenic elements, and the synthesis of organic molecules and driving of prebiotic chemistry. Another major theme is the multiple layers of shielding of planetary surfaces from the flux of cosmic radiation and the various effects on a biosphere of violent but rare astrophysical events such as supernovae and gamma-ray bursts. The influences of CR can also be duplicitous, such as limiting the survival of surface life on Mars while potentially supporting a subsurface biosphere in the ocean of Europa. This review highlights the common thread that ionizing radiation forms between the disparate component disciplines of astrobiology.

Supernovae, neutrinos and the chirality of amino acids

A mechanism for creating an enantioenrichment in the amino acids, the building blocks of the proteins, that involves global selection of one handedness by interactions between the amino acids and neutrinos from core-collapse supernovae is defined. The chiral selection involves the dependence of the interaction cross sections on the orientations of the spins of the neutrinos and the (14)N nuclei in the amino acids, or in precursor molecules, which in turn couple to the molecular chirality. It also requires an asymmetric distribution of neutrinos emitted from the supernova. The subsequent chemical evolution and galactic mixing would ultimately populate the Galaxy with the selected species. The resulting amino acids could either be the source thereof on Earth, or could have triggered the chirality that was ultimately achieved for Earth's proteinaceous amino acids.