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Richard N. Boyd Sonoma County Center for Astrophysics Michael A. Famiano

Stardust, Supernovae, Neutrinos, and the Molecules of Life (Why are the amino acids all left-handed, and what does that tell us about the origin of life?). Richard N. Boyd Sonoma County Center for Astrophysics Michael A. Famiano Western Michigan University Toshitaka Kajino and Takashi Onaka

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Richard N. Boyd Sonoma County Center for Astrophysics Michael A. Famiano

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  1. Stardust, Supernovae, Neutrinos,and the Molecules of Life(Why are the amino acids all left-handed, and what does that tell us about the origin of life?) Richard N. Boyd Sonoma County Center for Astrophysics Michael A. Famiano Western Michigan University Toshitaka Kajino and Takashi Onaka University of Tokyo NAOJ Visiting Fellow Workshop October 17-19, 2012

  2. Outline This talk covers a lot of different areas of science, so it will be pretty basic on all of them! What are amino acids and why do we care about them? What is chirality and how does this affect the amino acids? A little bit of history of the subject. Why/how do we think complex molecules are formed in the interstellar medium? What are core-collapse supernovae, and how might they affect the amino acids formed in space? Magnetic fields Neutrinos A little nuclear physics A model for molecular chiral selection Local replication/amplification of amino acids formed in space Spreading of chiral amino acids throughout the Galaxy Conclusions

  3. Amino Acids Alanine & Valine, two naturally occurring amino acids. Amino acids are organic molecules containing an amino group (NH2 ), a carboxylicacid group (COOH), and any of various side groups. Amino acids are critical to life, as they are the building blocks of proteins, which are linear chains of amino acids. The proteins are created inside the cells from the existing bath of amino acids according to instructions contained in our DNA. Humans need ~20 amino acids to make all the proteins we require; we can produce half; the other half has to be supplied by our food. And there are many more amino acids besides these 20, ~200 are known; most do not naturally exist on Earth.

  4. Chirality (handedness) An object or a system is chiral if it cannot be superimposed on its mirror image. Chirality of a material can also be defined by the way in which it affects circularly polarized light; the effect will be different for left-circularly-polarized light than it will for right-circularly-polarized light. The amino acids that appear in nature are left-handed, although if produced in the laboratory they are equally likely to be right-handed. This is curious! Some definitions: Dextrorotary—right handed Levrorotary—left handed Enantiomer—a chemical with a preferred chirality L D Racemic—equal parts D & L Enantiomeric excess = ee = (D - L)/(D + L)x100%

  5. Basic Question: Where Did the Amino Acids Come From? This is a question of the origin of life: where did the molecules of life originate? Were they produced in some Earthly cauldron? Or were they brought here by a cosmic stork? And are the molecules of life on Earth the same as those in other parts of the Universe? Are there molecules of life elsewhere in the Universe?!

  6. Past Explanations of Amino Acid Origin/Chirality • Pasteur first discovered a “demarcation line” between life and nonlife: the “mirror dissymmetry of organisms.” • Miller-Urey: Amino acids were produced by lightning in an appropriate environment on Earth (didn’t know about chirality) • Then they’re made chiral by circularly polarized photons from the Sun (difficult) • Panspermia hypothesis—”seeds” of life have an extraterrestrial origin • Seeds have always been here—revise big bang scenario (Not likely!) • Seeds brought to Earth by an advanced civilization • Chiral amino acids produced by circularly polarized uv light in space? Then delivered to Earth. • This is the currently favored model • Weak interactions • -β-decays of 14C would produce chiral Bremsstrahlung, which would result in selective destruction of molecules of one chirality (Effects are very small: ~10-12) • -Cline; neutrinos from SNe on 1H could do the processing (Effects are even smaller) • -Boyd, Kajino, Onaka; SN neutrinos selectively destroy 14N, which is coupled to molecular chirality, so this destroys one chirality, thus selecting the other. • Supernova Neutrino Amino Acid Processing Model: SNAAP Model

  7. Murchison Meteorite On 28 September 1969 at about 10:58 AM, near the town of Murchison, Victoria, Australia, a bright fireball was observed to separate into three fragments before disappearing. Many specimens were found over an area larger than 13 km², with individual masses up to 7 kg.The total collected mass exceeded 100 kg. The Murchison Meteorite contained more than 70 amino acids; they ARE made in outer space. Panspermia lives! (sort of, anyway) MM amino acids are either left-handed, racemic, or non-chiral. How/why did they get that way? But were the samples contaminated? A Murchison meteorite specimen at the National Museum of Natural History (Washington)

  8. Structure of 2-a-2,3-dmpa, a not naturally occurring amino acid. It has two chiral centers &, thus, four stereoisomers: the D & L formsof -methylisoleucine & -methylalloisoleucine. These gave ee’s = ~7% Chirality of the Amino Acids-Murchison MeteoriteFrom Cronin and Pizzarello, Science Magazine, 14 Feb., 1997 A) Isovaline, B) α-methylnorvaline, C) α-amino-n-butyric acid, D) norvaline. A and B gave ee’s 8.4% (& 18%; Glavin and Dworkin!) & 2.8%, but C & D (“unmethylated versions” of A & B) gave zero. A does not occur naturally, & B has “restricted distribution”. Original MM analyses gave ee’s of naturally occurring amino acids, but were those strictly Earthly? Cronin and Pizzarallo showed that at least some nonzero ee’s must have been produced in outer space.

  9. Other Meteorites? Another meteorite: Orgueil. It also had amino acids; Dworkin and Glavin found an ee for L-isovaline in Orgueil of 15%. Also Tagish Lake, Murray, and Allende—same result. Some Questions Might amino acids be produced in cosmic dust grains? Bernstein et al. (2002) showed that (non-chirally selected) amino acids (glycine, alanine, serine) could be produced in the lab via uv photolysis of interstellar ice analogs (H2O, NH3, CH3OH, HCN). Chiral selection could come later. This class of experiments was summarized by Allamandola (2008) Why are some meteoritic amino acid ee’s = 0? Amino acids might have gotten thermalized in transit; some are more resistant to radiation and shock than others. Some molecular configurations are harder to make chiral, or may not amplify (aqueous autocatalysis) as easily as others.

  10. Establishing and Amplifying Chirality • Glavin et al. analyzed many meteorites that had amino acids, and different amounts of aqueous alteration. Conclusions: • Aqueous processing appears to be important; more water seems to lead to greater ees. • Different forms of an amino acid can have very different aqueous alterations, hence very different ees. • Only L amino acids are found (or racemic AAs) suggesting that L amino acids are established very early on.

  11. Running Summary • So amino acids are definitely made in outer space, and they have the correct chirality, which is not so easily selected if the amino acids are made on Earth

  12. Cas A; Credit: X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA/JPL-Caltech/Steward/O.Krause et al.

  13. SHELLS OF A MASSIVE STAR AFTER Si BURNING Non-Burning Shell H-Burning Shell He-Burning Shell C-Burning Shell Ne-Burning Shell O-Burning Shell Si-Burning Shell Fe-Ni Core Where do the Elements (Especially C,N,O) Come From? • A star begins its life by burning the H in its core. • When the H, and the pressure that H burning produced, are gone, the star contracts, T , and He burning ensues. • This arrests further contraction until the He is gone, then another contraction occurs, until T enough to burn C. • When the C is gone, … • Following Si burning the core collapses, then the star explodes, and seeds the interstellar medium with its newly synthesized nuclides. The figure indicates both the order by which the elements are burned, and the “onion skin like structure” of a massive star that has completed all its stages of stellar evolution.

  14. Core-collapse Supernovae, magnetic fields, and neutrinos - I Neutrino spectrum (Gava et al.) for two assumptions of processing Core-collapse Supernovae? Massive stars (M > 8 solar masses) will complete all their stages of evolution and then collapse to a neutron star or black hole. They expel nearly all of their core energy (resulting from gravity) by emitting 1057 (1053 ergs of) neutrinos in ~10 seconds. Some neutrino properties: Neutrinos are nearly massless particles, have zero charge, and interact through the weak interaction. There are 3 flavors: electron, muon, and tau, and each has its corresponding antiparticle. Because they have such small masses, they are relativistic, so their spin (1/2)ħ will either align or anti-align with their momentum: Electron neutrinos have negative “helicity” (anti-aligned) Electron antineutrinos have positive “helicity” (aligned)

  15. Core-collapse Supernovae, magnetic fields, and neutrinos - II Neutron Star B B What is the magnetic field B from a collapsing neutron star or black hole? It will be dipolar It can be very strong—more than 1014 G at the surface of a neutron star (radius = 10 km) B = (μoM/4π)r-3[(r/r)2cosθ+(θ/θ)sinθ] On one side of the neutron star B and the anti-neutrino spin will be aligned, but on the other side they’ll be anti-aligned. Since B will also align molecular angular momenta via the molecular magnetic moment, the anti- neutrino spin will also be aligned therewith on one side and antialigned on the other.

  16. 5.14 2mec2 0.06% 3.95 14O 99.3% Some Gentle Nuclear Physics 2.31 0.61% 0.16 100% 0.00 14C 14N β-decay scheme for mass 14 nuclei. Energies are in MeV. Electron neutrinos (νe) and antineutrinos (νe) interact with 14N: νe + 14N → e+ + 14C, Q = - 1.18 MeV (G-T transition) νe + 14N → e- + 14O, Q = - 5.14 MeV (G-T transition) The first reaction (0.16 MeV + 2mec2) is more likely to go than the second, given the Eυ’s (~12 MeV). Also, σ ~ (Eυ – |Q|)2, enhancing the effect.  When the νe spin and the 14N spin (=1 Ћ)are aligned, their total spin must be ½ + 1 = 3/2. When they are anti-aligned, the total spin can be either 3/2 or ½; the fractions are well defined ( ½, 2/3 of time). But 14C is a spin zero nucleus, so the final state total spin will be ½ (= ½ + 0). Total angular momentum must be conserved: one additional unit of orbital angular momentum transfer is required (from the νe or e+ wave function) in the aligned case, but none in the anti-aligned case. This inhibits that transition by ~ x10. Thus the transition will be less probable for the aligned case, so destruction of 14N, hence the molecule to which it is attached, is more likely for the anti-aligned case.

  17. Chiral Molecules and 14N m/ħ How does this affect molecules? The molecules will have some total angular momentum that will interact with the magnetic field. Buckingham has developed a model (for NMR) for these molecules that applies also to our case. Chiral selectivity requires a net odd parity operator; time reversal symmetry allows a rotating nuclear magnetic moment mx(N) (odd under time reversal, parity even) to induce a molecular electric dipole moment my(M) (even under time reversal, parity odd), in an external Bz; the resulting effect is opposite for D and L enantiomers. THIS REQUIRES A NON-ZERO SPIN NUCLEUS. For example, assume the total angular momentum is 3ħ/2, which will have the projections along Bz as shown. In thermal equilibrium, and with Bz = 0, these four levels will be equally populated. 3/2 1/2 -1/2 -3/2

  18. Neutrinos, magnetic fields, and molecular chirality m = +3/2 However, the effect of the Buckingham effect is to drive the populations away from equality, as suggested in the figure below (where the width of the line indicates the relative population): Antineutrinos will do a chiral selection at each throat; the SNL that aligns with Sν at the LHS will let more NL than NR live there. But the opposite effect occurs at the RHS; there NR prevails, if nothing else happens. But (Horowitz &Li, Arras & Lai, Lai & Qian, and Maruyama et al.): B affects the neutrino absorption cross sections, so that the neutrino luminosity, hence the ee, might be 20-30% higher at one neutron star throat than at the other. This WILL give an overall ee. m = +1/2 m = -1/2 m = -3/2 No Magnetic Field Magnetic Field, LH Molecules Magnetic Field, RH Molecules The 14N’s that live will give their molecules a preferred chirality.

  19. Running Summary • So amino acids are definitely made in outer space, and they have the correct chirality, which is not so easily selected if the amino acids are made on Earth • Combination of magnetic field and electron antineutrinos from core-collapse supernovae, together with the spin alignment of 14N, do select a preferred amino acid chirality

  20. Amplification of Chirality in the Interstellar Medium—I The ee’s produced in any existing model are really small. In the SNAPP model, the volume each SN would process times the number of SNe occurring in the lifetime of a “giant molecular cloud”, in which complex molecules are thought to be made, is <<< the size of the cloud. But once created, the molecules will replicate, possibly on warmed (more than 20 K) dust grains that exist in the clouds or on comets. Gol’danskii and Kuz’min: autocatalysis; two effects could contribute: - “Advantage,” e.g., via circularly polarized light, weak interaction (or supernova neutrinos!) to initiate ee. -Kinetic, i.e., through reactions, originally due (sort of) to Frank (1953) (where the k’s indicate the reaction rates): A+B ML (k1L) A+B MD (k1D) A+B+ML 2ML (k2L/k-2L) A+B+MD 2MD (k2D)/k-2D) ML+MD A’ (ks) These reactions probably could not produce ee’s via thermal fluctuations. But if the kL and kD are different, these can amplify ee’s initiated by some other mechanism.

  21. What About all those Supernova Photons? But wouldn’t the photons from the supernovae destroy all the chiral molecules just processed by the neutrinos? There aren’t as many of them as there are neutrinos, but their interaction cross sections are >>> than those of the neutrinos. If the end state of the supernova is a black hole, the collapse to the black hole might result before any of the photons could escape (since it takes them ~hours to get out). The neutrinos only need ~seconds to get out! And black holes aren’t rare; they occur a reasonable fraction (~20%) of the time. But the progenitor star can’t be too large; a red giant (progenitor of core collapse supernovae) would encompass the entire region that might be processed. So progenitors need to be “Wolf-Rayet” stars, which shed their H and/or He shells, creating clouds, and ultimately produce Type Ib or Ic supernovae (which DO produce black holes).

  22. How Large a Region Gets Processed by the Neutron Star? • Assume N-star’s magnetic field orients out to radius at which it is equal to the ambient galactic magnetic field, ~10-6 gauss. • Assuming it’s 1014 gauss at N-star’s surface (10 km), that’s 5x1012 cm. • Also assume that the processed volume has to be appreciably larger than the N-star’s progenitor: • The Sun’s radius is 7x1010 cm • A Red Giant’s radius is 1.4 to 5.6x1013 cm • But massive star (Type Ib or Ic) supernovae (which collapse to black holes) have progenitors with radii < than that of the Sun. • For reference, Earth’s orbit is 1.5x1013 cm. Processing probability along polar axis logsn Fn -12 -10 -8 -6 -4 -2 10 11 12 13 14 log r (cm) Radius of Type Ib or Ic progenitor Solar radius Earth orbit Red Giant radius range

  23. Where Is the Largest Enantiomeric Excess Created? B • Bulk Polarization of molecules as a function of polar angle shows a sharp peak. • This is for B~1 gauss (@ 0.1 AU); peak is sharper at higher B-field. • Processing probability is largest at zero polar angle. • Neutrino asymmetry is largest at zero polar angle. So zero polar angle is where everything is optimum. Amplification of the EE will occur most rapidly where the EE is large. So the maximum values are what are most relevant. ω J

  24. Can Molecules Live Close to a Wolf-Rayet Star? General conclusion: Progenitor star is too hot to produce or accomodate molecules; they are produced in the giant molecular clouds in which the W-R stars reside. They are transported to the vicinity of the W-R star by the grains or meteoroids on which they formed. W-R stars are hot—50,000 K—uv and x-rays! But the clouds produced by their winds, and the short passage time as the grains or meteoroids (which might be agglomerations of grains) pass through the clouds, would allow the molecules to survive. There will be lots of such grains or meteoroids within 1 AU of the W-R star at any given time; these are what get processed by the neutrinos when the supernova occurs. What level of enantiomerism would be produced? (1057/4πr2) σ = 5x10-7 at r = 0.01 AU. It might be larger; Lunardini (2009) showed that the fraction of νe’s is larger, and the energy is higher, for massive stars. But bulk polarization is ~1% at best. And other effects might make it smaller. This is the maximum value, but that’s what you want!

  25. Running Summary • So amino acids are definitely made in outer space, and they have the correct chirality, which is not so easily selected if the amino acids are made on Earth. • Combination of magnetic field and electron antineutrinos from core-collapse supernovae, together with the spin alignment of 14N, would select a preferred amino acid chirality. • A volume surrounding a Wolf-Rayet star does exist in which molecular processing (of meteoroids) would occur, and large meteoroids wouldn’t be completely destroyed. Maximum processing would be along the poles of the nascent neutron star.

  26. Amplifying the Chiral Selectivity Experimentally:Autocatalysis Works! • Lab experiments: samples with “some” ee can be driven to higher chiral selectivity. Water is important; so the warmed ice surfaces of the dust grains, or planetary surfaces (!), are favored sites. Examples: • Soai et al. 1995: 2% ee 5-pyrimidyl alkanol treated with diisopropylzinc and pyrimidine-5-carboxaldehyde undergoes autocatalysis to 85% ee. • Soai and Sato 2002: 0.05% ee of methyl mandelate autocatalyzed to high ee. Leucine (an amino acid) at 2% ee was also enhanced to >95% ee. • Mathew et al. 2004: 5% ee proline yielded an ee of 65%, but the reaction rate was observed to increase with ee. • Breslow and Levine 2006: 1% ee samples of D- or L-phenylanine were amplified to an ee of 90% by two evaporations to precipitate the non-chiral component. • Is there a minimum ee that would allow amplification? Minimum value studied is < ~0.1%, but we don’t know where threshold is at present.

  27. Spreading Chirality Throughout the Galaxy Having established left-handed amino acids in blotches within a giant molecular cloud, might this get propagated throughout the Galaxy? Probably—there are several processes by which this can occur. They include “many types of astronomical sources, including planetary nebulae, wind- blown bubbles, supernova remnants, starburst superwinds, and the intercluster medium” (from Pittard (http://adsabs.harvard.edu/abs/2007dmsf.book..245P) Some indication of the mixing time for this is given by the rotation time of the Milky Way; it is thought to have rotated several times during its ~12 Gy lifetime.

  28. Running Summary • So amino acids are definitely made in outer space, and they have the correct chirality, which is not so easily selected if the amino acids are made on Earth. • Combination of magnetic field and electron antineutrinos from core-collapse supernovae, together with the spin alignment of 14N, would select a preferred amino acid chirality. • A volume surrounding a Wolf-Rayet star does exist in which molecular processing (of meteoroids) would occur, and large meteoroids wouldn’t be destroyed. Maximum processing would be along the poles of the nascent neutron star. • Although enantiomeric excess would initially be small (although relatively large in the SNAAP model!) amplification and mixing mechanisms exist for spreading the resulting chirally selected amino acids throughout the Galaxy.

  29. Mostly Likely Competing Model: Chirality from Circularly Polarized Light—in Outer Space—1 • Experiments have shown that CP light can produce enantiomerism • CP light has been detected from outer space at the <1% level. Also from the Sun. Both sources are multiply scattered light. • CP light might polarize amino acids in outer space, which could then be transported to Earth • Cross sections for this process are >>> than those for the neutrinos • Bailey model (1): • Amino acid chirality established from CPL on (small) dust grains in reflection nebulae • Polarization can be high (Gledhill & McCall); scattering from aligned grains can give 50% or even higher • After ee is established, grains clump, then agglomerate to form meteoroids • This would be the scenario if life in the Universe is common • Critique: • Processing small dust grains, then letting them agglomerate into larger entities gets around problem of producing chirality throughout the volume of objects large enough to get through planetary atmospheres • Timing is tricky; amino acids in such environments may only live several hundred years, processing to large ee may take thousands of years, and grains may form too rapidly

  30. Mostly Likely Competing Model: Chirality from Circularly Polarized Light—in Outer Space—2 • Bailey model (2): • Amino acid chirality could be established from CPL from a magnetized white dwarf from matter accreting onto the poles • This has high polarization—as high as 50% has been observed • But this is a rare event; it might prevail if life in the Universe is rare • Critique: • Same problem as for model #1 for timing of the relevant processes for getting processed amino acids to planetary surfaces. • For both models, CP light has to destroy most of the molecules to create any ee—100% polarized CPL gets 10% ee after destroying 99.6% of amino acids • And CP light would produce both LH and RH molecules, although in different places. But if we ultimately see equal populations of LH and RH amino acids, this model wins. • Amplification and mixing mechanisms seem adequate to support either the CP light or the SNAAP model.

  31. To Circumvent the RH here, LH there Issue … Since the only data we have, probably for a long time, are from the Solar System, this might provide a plausible explanation. But questions remain unanswered. We need a hyperbolic comet!

  32. Poor Statistics Earthly amino acids are all LH, but perhaps all of them should be LH if one is? The only extensive extraterrestrial samples of amino acids are from the Meteorites that get to Earth. Those are either racemic or LH. Another possible test: ROSETTA will sample amino acids on comet 67P/Churyumov-Gerasimenko in 2014. Rosetta will test these models; only LH amino acids would support the SNAAP model. A mixture of LH and RH amino acids would support the circularly polarized light model, but only LH can’t rule it out. So far, the SNAAP model looks good, but on limited statistics!

  33. What About the Other Molecules of Life—DNA/RNA? • One possibility: Once the amino acids got to Earth (via meteorites) they could have made peptides, which may be able to evolve into nucleobases, the constituents of DNA and RNA. • Another possibility: the nucleobases were made in space and transported to earth by meteorites. • Callahan et al. (2011) searched for nucleobases in meteorites, (especially MM) and found adenine and guanine, two of the five bases (also cytosine and thimine/uracil). They also found other • non-naturally occurring chemicals that are made via the same processes that make nucleobases. • Earlier studies also claimed detections of nucleobases in MM, but samples may have been contaminated. • One other study, that of Martins et al. (2008), was probably valid; they found uracil. So all the basic ingredients for life appear to be made in outer space.

  34. When/How Did Life on Earth Begin? • Once slightly chiral species got to a planet, the above experiments suggest they could be driven to homochirality in whatever chirality had the edge before they got to the planet. And there were probably lots of meteoroids that got to Earth, or any other planet, so the chirality that dominated in outer space would win every time. • The Moon, and therefore Earth, were bombarded by tremendously intense meteor showers until 3.8 billion years ago. (Jupiter swept the inner solar system clean) • And life is thought to ‘have begun’ on Earth shortly after that. Is that a coincidence??

  35. Racemic mixture of amino acids forms in grains and meteoroids in Supernova nebulae (same number of and ) Neutrinos from other (massive) Supernovae convert racemic to enantiomeric molecules via selec-tive destruction of one chirality of 14N-based molecules Supernovae synthesize C, N, O, etc. Subsequent generations of stars form, along with planets and biological forms, and evolve to homochiral mole-cules via more amplification when they arrive on planets “Rapid” chemical evolution amplifies the enantiomerism as the material in the molecular clouds “slowly” expands to fill the galaxy (more than ) To Summarize: So our origins may lie in outer space!

  36. Supernovae, Neutrinos and the Chirality of Amino Acids, R.N. Boyd, T. Kajino, and T. Onaka, Int. J. Mol. Sci. 12, 3432-3444 (2011)

  37. Be careful whom you call “alien,” brother!

  38. Creation/Amplification of Chirality in the Interstellar Medium—II • Circularly polarized light: CPL? Experiments have shown that this can produce nonzero ee’s. However, fraction of cpl << 1%, both in sunlight and in uv from, e.g., neutron stars. This is the current leading candidate for the initiator of amino acid chirality. • Weak interaction effects? Might they produce a DE that would favor one chirality, so would permit auto-catalysis MC, A + B + MC → 2MC (Mason and Tranter)? Unfortunately, DE /kT is very small: ~10-17. None the less, chirality, once established, can last for a long time, at least for some molecules. Previously mentioned, betas from beta decay produce chiral Bremsstrahlung which can selectively destroy one chirality. • Another possibility: Catalysis via radicals formed in grains by interaction of pre-formed molecules, perhaps already chiral, by high energy cosmic rays (Garrod et al.). nL/nD ?? What is the timescale for the replication processes? Giant molecular clouds exist for ~20 million years, and they have many complex molecules. So the replication processes must be faster than that.

  39. Might the SNAAP Model Produce RH Molecules? We ignored the possibility of νe+14N 14O+e-; this can still occur. And it would have the same spin alignment features that the νe+14N 14C+e+ reaction had, i.e., selective destruction, but this would favor right-handed amino acids! However, it occurs in the same space as the other reaction, so could not produce net RH molecules. However, RH molecules would be produced preferentially at the “other” throat of the neutron star. So if the two regions were not well mixed, there could be pockets of RH molecules. But this seems highly unlikely. So this is an interesting prediction of the SNAAP model! But we clearly need better statistics from meteoroids, or comets (ROSETTA should provide a crucial test!). So far everything seems LH or racemic, and the statistics are becoming impressive!

  40. Might Other non-zero Spin Nuclei Affect the SNAAP Scenario? 2H? This is a part in 104 of normal H, so would be an infrequent component of the amino acids. It also wouldn’t be as selective as 14N, since the Q-values going to two neutrons or two protons are similar. 1H? It has a spin of ½, so wouldn’t provide the total angular momentum extremes that 14N does. Also, the transition is a mixture of “Gamow-Teller” (which requires a change in nuclear spin of 1 unit, so is what mediates the 14N transitions) and “Fermi” (which requires no change in nuclear spin), which further muddies the transition possibilities. 13C? Too rare to compete with 14N. 15N? Very rare—too rare to have any effect.

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