Astrobiology, homochirality, and origin of life Axel Brandenburg, based on work with Anja Andersen, Martin Nilsson, Susanne Höfner, Tuomas Multamäki, Harry and Kirsi Lehto (Nordita) Astrobiology in Nordic countries Role of Nordita Meetings: Copenhagen, Turku, Oslo, Stockholm Winter school last January Our current interests: homochirality and origin of life peptide world, RNA world Stockholm Observatory, Astronomy seminar, September 29, 2006 Int. J. Astrobio. 3, 209 (2004), 4, 75 (2005), Orig. Life Evol. Biosph. 35, 225 (2005), 35, 507 (2005)

Astrophysics: staff and duties Nordita in Copenhagen

Nordita in Stockholm Expected developments ~6 new post-docs Nordic+non-Nordic ~2 new assist. profs ~5 programs/year visiting professors (1/2-2yr) Nordita-days next August

AB-School Jan 2004 Copenhagen Aug 2004 Turku Jan 2005 Copenhagen Nov 2005 Oslo Jan 2006 Kittilä

Topics at Nordic AB meetings Atmospheric escape Martian gullies Icelandic analogues Subglacial lakes Geological evolution Cyanobacteria Deep biosphere Extremophiles Deep biosphere Meteorites stardust RNA world geochemistry Nucleotide Synthesis In space Deep biosph Ancient DNA, PNA, Early life evidence Climate, exoplanets Mars simulator Interstellar chem.

Frozen/liquid water on Mars On Earth: Life 3.8 Gyr ago Frozen/liquid water on Mars

Astrobiology: The range of problems From dust to planets Exoplanets Water delivery Habitable worlds Archaen world Volcanoes, carbon cycle Impacts, panspermia Greenhouse effect Miller experiment Amino acids, chemistry Artificial life Origin of life RNA world, TNA, PNA homochirality Early life Extremophiles Cyanobacteria Oxygen, methane evol.

Remaining dust settles Time line 104 yr 106 yr 108 yr 109 yr First life planetesimals Sun ignites T0=1010 yr after Big Bang All gas gone Remaining dust settles

Amino acids in proteins: left-handed Sugars in DNA and RNA: right-handed Is chirality: (i) prerequisite (ii) consequence of life? carboxyl group Louis Pasteur (1822-1895) animo group chlorophyll

Producing enantiomeric excess (e.e) Life only develops in homochiral environment Homochirality is a prerequisite However: no mechanism produces 100% e.e. only minute partial excess possible (electroweak) slightly bigger for large Z, goes like Z5  Cu (II) ions Still need amplification mechanism Frank (1953) model (plus extensions): nucleotides Autocatalysis and enantiomeric cross inhibition Plasson, Bersini, Commeyras (2004): peptides

Chirality selection during polymerization of the first replicating molecule? lipid world? Peptide world, PNA world RNA world dual world achiral RNA DNA RNA proteins chiral Rasmussen et al (2003 Artif. Life 9, 269-316) Isotactic polymer (same chirality) R Monomers to dimers “waste” (enantiomeric cross-inhibition) L

RNA and peptide worlds Polycondensation reactions Isotractic chains strongly preferred Self-amplification conceivable Initially (nonliving): e.e.=0 During polycondensation: e.e. ~ exp(lt) l is the growth rate

RNA versus peptide worlds RNA world peptide world Activation D  D*, L  L* Polymerization D+D DD, L+L  LL Epimerization DL  LL, LD  DD Depolymerization DD  D+D, LL  L+L Template-directed (PCR-like) Enantiomeric cross-inhibition Autocatalytic production of new mono-nucleotides ( but uncertain) APED model (Plasson et al.)

Recap of Frank-type model (Frank 1953) auto-catalysis alone kinetic equation exponential growth enantiomeric excess: catalyst

Need mutual antagonism add cross-inhibition kinetic equation unspecific antagonism

Initial bias not necessary Exponential amplification Initial excess can be virtually zero Initial bias may not change this depends on strength Second genesis: other chirality? would be cool but is not necessary Bifurcation diagram with Andersen, Höfner, Nilsson Orig. Life Evol. Biosph. 35, 225 (2005) fidelity

Relevant experiments: autocatalysis now also: proline-catalyzed reaction (Blackmond 2004) pyrimidine-5-carboxylaldehyde with diisopropylzinc  autocatalytic self-amplification cf. Frank (1953), Goldanskii & Kuzmin (1989), … Soai et al. (1995) self-amplification + competition important

Relevant experiments: nucleotides  Mononucleotides with wrong chirality terminate chain growth ok poisoned template-directed oligomerization poly (CD)  oligo (GD) (using HPLC)  enantiomeric cross-inhibition cytosine guanine Joyce et al. (1984)

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

Relevant experiments: crystals Crystal growth, many different nucleation sites: racemic mixture Crystal growth with stirring: primary nucleation suppressed Kondepudi et al. (1990)  competition important

APED model (Plasson et al. 2004) a: activation p: polymer. a: inhibition h: depolym. e: epimerization on N-terminal DLLL not DL DD

APED model equations Consider limit of large h and e

APED model equations limit of large h and e corresponding reaction  D catalyzes conversion of both D* and L* into D

APED model equations additional limit of large p corresponding reaction APED model is auto-catalytic after all! subtract

Where could this work? a) hydrothermal vents b) Tides Braun & Libchaber (2003) b) Tides Lathe (2003)

Early forms of protocells Michael J. Russell (2006, Am. Sci. 94, 32-39)

Spatially extended model with Tuomas Multamäki, Int. J. Astrobio. 3, 209 (2004) Reaction-diffusion equation 1350 1349 Proto type: Fisher’s equation 1348 Propagating front solutions wave speed 1347 Spread of the black death

1D and 2D models (reaction-diffusion equation) Propagation into racemic environment Disappearence of isolated islands

Piecewise linear increase Reduced equations add/subtract:

Effects of turbulence

Pencil Code Started in Sept. 2001 with Wolfgang Dobler High order (6th order in space, 3rd order in time) Cache & memory efficient MPI, can run PacxMPI (across countries!) Maintained/developed by ~20 people (CVS!) Automatic validation (over night or any time) Max resolution so far 10243 , 256 procs Isotropic turbulence MHD, passive scl, CR Stratified layers Convection, radiation Shearing box MRI, dust, interstellar Sphere embedded in box Fully convective stars geodynamo Other applications Homochirality Spherical coordinates

Conclusions Astrobiology: need to be prepared… Polymerization model: Based on measurable processes Reduction to accurate simplified model Homochirality in space (earth, interstellar, etc) Timescales 500 Myr; fossil evidence of spatially fragmented homochirality? Pencil Code: just google for it Detailed manual, …