Topics in Astrobiology 1.What is and can be done 2. The problem of chirality

2 The range of problems 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

3 Rough time line 10 4 yr 10 6 yr 10 8 yr 10 9 yr planetesimals Sun ignites All gas gone Remaining dust settles First life

4 Time line (later)

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

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

7 Evaporation of LINEAR during fly-by. Cloud of hydrogen Estimated water content 3x10 9 kg (outgassed during fly-by) Obsered in Ly 

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

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

10 RNA itself as enzyme

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

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

13 Photosynthesis Requires chlorophyll As catalyst What about chiralitry?

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

15 Aminoacids in protein: left-handed Sugars in DNA and RNA: right-handed Louis Pasteur ( ) animogroup carboxylgroup

16 Racemic mixture (from lecture of Antoine Weiss) 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 template-directed oligomerization poly (C D )  oligo (G D )  Mononucleotides with wrong Chirality terminate chain growth cytosine guanine ok poisoned Joyce, et al. (incl. Orgel) (1984) (using HPLC)

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

20 Relevant experiments: crystals Crystal growth with stirring: primary nucleation suppressed Crystal growth, many different nucleation sites: racemic mixture 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 ~2 1-n

25 Coupling to substrate S Q L 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)  Q L = Q R (L n,R n ) Source of L 1 monomers Q L

26 Self-catalytic effect Form of Q L = Q R (L n,R n ) Possible proposals for C L (similarly for C R )

27 Birfurcation properties  Mononucleotides with wrong Chirality terminate chain growth

28 Stability Relative perturbation of racemic solution, 10 -4

29 Conservation law Dependence on fidelity where

30 Differences to Sandars Coupling to substrate: here proportional to E L –in Sandars: [L N ] 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