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Topics in Astrobiology

Topics in Astrobiology. What is and can be done The problem of chirality. From dust to planets Exoplanets Water delivery Habitable worlds Archaen world Volcanos, Carbon cycle Impacts, panspermia Miller experiment Amino acids, chemistry. Artificial life Origin of life

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Topics in Astrobiology

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  1. Topics in Astrobiology What is and can be done The problem of chirality

  2. From dust to planets Exoplanets Water delivery Habitable worlds Archaen world Volcanos, Carbon cycle Impacts, panspermia Miller experiment Amino acids, chemistry Artificial life Origin of life RNA world, TNA, PNA homochirality Early life Extremophiles cyanobacteria The range of problems

  3. Rough time line 104 yr 106 yr 108 yr 109 yr All gas gone Remaining dust settles planetesimals Sun ignites First life

  4. Time line (later)

  5. Source of the atmosphere Carbon cycle Venus, Earth: active volcanos: thick atmosph. Mars: Volcanos extinct

  6. Water deliveryvia comets Comet LINEAR: same HDO ratio as on Earth’s oceans cf. Hale-Bopp (too much)

  7. Evaporationof LINEARduring fly-by.Cloud ofhydrogen Obsered in Ly a Estimated water content 3x109 kg (outgassed during fly-by)

  8. Miller/Urey experiment Wait 1 week 15 organic compounds 2% amino acids (11 different ones)

  9. Walter Gilbert (1986) The RNA world • Central dogma of chemistry of life • DNA  RNA  protein enzyme • all enzymes are themselves proteins?

  10. RNA itself as enzyme

  11. pre-RNA worlds Many problems: stability of sugars 2-amino ethyl glycin (AEG)

  12. pre-RNA worlds better alternative: Nelson, Levi, Miller (2000) PE Nielsen (1993)

  13. Photosynthesis Requires chlorophyll As catalyst What about chiralitry?

  14. Homochirality:models and results Axel Brandenburg, Anja Andersen, Susanne Höfner, Martin Nilsson To appear in OLEB, q-bio.BM/0401036

  15. Aminoacids in protein: left-handedSugars in DNA and RNA: right-handed carboxyl group animo group Louis Pasteur (1822-1895)

  16. (from lecture of Antoine Weiss) Racemic mixture Racemization dating method

  17. Chirality and origin of life • Dead stuff not chiral, so is chirality • with racemic mixture: structure fragile • Importance: • Prerequisite of life (provides curvature and twist) • Consequence of life (enzymatic reactions) • Miller-Urey amino acids: both chiralities • in Murchison meteorite: mostly left-handed! • but contamination is debated… • Reasons discussed: circularly polarized light, beta-decay (weak force), homochiral template

  18. Relevant experiments: nucleotides  Mononucleotides with wrong Chirality terminate chain growth ok poisoned template-directed oligomerization poly (CD)  oligo (GD) (using HPLC) guanine cytosine Joyce, et al. (incl. Orgel) (1984)

  19. Contergan: was sold as racemic mixture Cures morning sickness during pregnancy causes misformations (abundaned in December 1961)

  20. Relevant experiments: crystals Crystal growth, many different nucleation sites: racemic mixture Crystal growth with stirring: primary nucleation suppressed Autocatalytic self-amplification? Frank (1953), Goldanskii & Kuzmin (1989), …

  21. Model by Saito & Hyuga (Jan 2004) Bimodal behavior

  22. Model by Sandars (Dec 2003, OLEB) Reaction for left-handed monomers Loss term for each constituent

  23. Combined equations Loss term for each constituent

  24. Including enantiomeric cross-inhibition Loss term for each constituent Racemic solution ~21-n

  25. Coupling to substrate S Source of L1 monomers QL QL comes from substrate acts as a sink of S S sustained by source Q Catalytic properties of substrate (depending on how much L and R one has)  QL = QR(Ln,Rn)

  26. Self-catalytic effect Form of QL = QR(Ln,Rn) Possible proposals for CL(similarly for CR)

  27. Birfurcation properties  Mononucleotides with wrong Chirality terminate chain growth

  28. Stability Relative perturbation of racemic solution, 10-4

  29. Dependence on fidelity Conservation law where

  30. Differences to Sandars • Coupling to substrate: here proportional to EL • in Sandars: [LN] • Outer boundary condition: here open • in Sandars: prescribed damping term • Future extensions: • Chain braking • add spatial 3D dynamics

  31. Reduced equations Quantitatively close to full model

  32. Initial bias Effect in reality very weak

  33. Conclusions • There are many astrobiology topics where astrophysicists can help out with their knowledge, as well as technical and computational tools • Homochirality is a hot one with several papers this topic in each issue of OLEB

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