Az exobiológiai kérdésektől az asztrobiológiáig: tudomány és mozgalom Szathmáry Eörs
ELTE Biológiai Intézet
Parmenides Foundation, München
Növényrendszertani, Ökológiai és Elméleti Biológiai Tanszék
Centre for the Conceptual Foundations of Science
Definíciók • Exobiológia: a földönkívüli élet lehetőségeivel foglalkozó tudomány (a romantikus kor) • Asztrobiológia: az élet eredetének, evolúciójának, eloszlásának és jövőjének tanulmányozása az Univerzumban (a mozgalom és a „cégérek átfestése”)
A romantikus kor egyik fő motivációja: a Drake-egyenlet
Az exobolygók
Upsilon Andromedae d, képzeletbeli holdakkal
Mit szeretnénk látni? • • • •
Civilizáció nyomát... De legalább sok oxigént... Vagy királis szerves molekulákat... Esetleg „csodákat”...
Mindenki söprögessen a saját háza előtt
Mars
Europa
Titan
Enceladus
A magyar csoport tagjai • • • • • •
Horváth András Pócs Tamás Kereszturi Ákos Bérczi Szaniszló Sik András Gánti Tibor +
A csoport tevékenysége Analyzing the possibilities of life on Mars in the Polar Regions by • Mars observations, • model computations, • analogous organisms on Earth.
Mars: egy halott bolygó (?) •Nagyon száraz: nincs víz •Nagyon hideg (-130 C)
•Erős UV-sugárzás (above 190 nm) •Ritka légkör(6 mbar)
A nedvesség ciklikus változásai
A Mars felszíne • thin CO2 atmosphere, pressure 6-8 mbar • temperature -50 C (between +10C -160 C) • reddish desert • pink sky • seasonal changes • dust storms
Jég és víz
Ices on Mars • water ice • carbon-dioxide ice
H2O budget: • small as water wapor (atmosphere, 1-100 prm) • most in frozen water ice (on and below the surface, 100-500 m)
Polar Regions • permanent ice cap • seasonal ice cap • by condendation • by snow fall • layered: H2O ice below, CO2 ice above
Surface conditions: • T, p usually below triple point • atmosphere very dry • water ice usually sublimates before melts
Sötét dűnefoltok, mint lehetséges élőhelyek (2001)?
Sötét dűnefoltok • dark patches • springtime in seasonal frost • on dark basaltic sand dunes • at high latitude
Dark Dune Spots (DDSs) • dark patches • springtime in seasonal frost • on dark basaltic sand dunes • at high latitude • characteristic structure • annual re-occurrence
A lefolyások 2 groups: • diffuse on horizontal surfaces too, wind blown, CO2 related • confined only on slopes (H2O cover) flows
Mozgásban... • daily movement 1 m/sol • in branches • sometimes accummulate in „ponds”
Egy mozgókép kockái
Egy lehetséges biológiai hipotézis 1. Tavaszi napsütés - szublimáció CO2 sugarak 2. A napsugárzás behatol a CO2 jég lyukaiba – felmelegíti a bazaltszemcséket a vízjég alatt 3. Interfaciális víz keletkezik naponta 4. A hipotetikus Marsi Felszíni Organizmusok metabolizálnak 5. Évszakos lefolyások 6. A felszín leszárad, az organizmusok beszáradnak 7. A következő marsi évben kezdődik előlről
Surfaces & Water: Adsorption, freezing, interfacial water, brines - I
1. Cold mineral surface, exposed to water vapour
Water vapour
Mineral/salt surface
Adsorption and freezing will form water ice between mineral/salt-surface and water vapour
Water vapour
2. Freezing of (adsorbed) water
Water ice
Mineral/salt surface Water ice on a mineral/salt-surface is thermodynamically not stable
Möhlmann, Budapest, 23. November, 2009
Surfaces & Water: Adsorption, freezing, interfacial water, brines - II Liquid interfacial water forms between ice and mineral/salt-surface Water vapour
3. Liquid interfacial water between ice and mineral/salt
water ice 1 nm
liquid-like mono-layers of water
Mineral/salt surface A solution can evolve in the interfacial water above the mineral/salt surface
Water vapour
4. A low temperature brine forms with salt and interfacial water
water ice Brine
Mineral/salt surface Möhlmann, Budapest, 23. November, 2009
The idea that brines can form liquid aqueous solutions on Mars is not new: It has been studied by Farmer (1976), Clark (1978), Brass (1980), Clark and Hart (1981), Bryson et al. (2008), Haberle et al. (2001), … and many others And in course of Phoenix in 2009 by Hecht, Chevrier, and Renno.
Brines can remain liquid far below 0° C Fe2(SO4)3 until 205 K, e.g. (48 % b.w. - Chevrier et al., 2008, 2009) Phoenix-imaging, NASA
First images of liquid droplets of brines (yet in discussion) - Phoenix-Mission Nilton Renno et al., (2009) Möhlmann, Budapest, 23. November, 2009
Sol 8 14:45 LMST
Oblate spheroids grew by deliquescence on splashed material (saline mud ?) Two spheroids seem to merge
Möhlmann, Budapest, 23. November, 2009
Sol 31 13:28 LMST The large spheroid has become darker The diffuse component of scattered light is reduced by 1/n2 (n - refractive index). n-ice :1.31 n-water:1.33 n-brine:1.4 Liquefaction darkens ! The large spheroid liquified and could drip
Möhlmann, Budapest, 23. November, 2009
Sol 44 14:35 LMST The large spheroid has dripped
Möhlmann, Budapest, 23. November, 2009
És mégis van víz a foltokban!
Ahogy kell: néhány tíz mikronnyi vízjég • The lowest albedo is found in the core (C), which is H2Oice poor and shows some CO2 ice signature (from atmospheric dust scattering of outer surfaces and/or from the surface). • The outer ring (R) corresponds to a local minima in albedo with an elevated H2O ice signature a low CO2 ice signature. • The high CO2 signature of the bright halo (H) and the average frost covered terrain (F) is also marked, while slope effect (SE) is indicates an elevate value on sun-facing slope.
Brine, Lake Magadi, the Rift Valley
Saturated solution, flamingos are eating cyanobacteria and algae
Shott el Jerid, Sahara
Cyanobacteria survive in the brine-mud below 1-2 m of dry salt, colour the water to deep blue in the rainy season
Salt lake in Australia
The coloured layer is the cryptobiotic crust
Blood Falls (Taylor glacier, McMurdo Dry Valleys)
Perchlorate reduction in brines • In simulated brines containing 7.5% total solids, the Citrobacter sp.,significantly reduced both perchlorate and nitrate with 34.9 and 15.6% reduction, respectively, in 1 week. • Coculture of a potent perchlorate reducing, non-salt tolerant (non-saline) bacterium and the Citrobacter sp. proved most effective for perchlorate removal in the brine (46.4% in 1 week). • This study demonstrates that both anions can be reduced in treatment of brines from ion exchange systems.
The picture of Buford Price
Price’s conclusion (2004) • Our results disprove the view that the lowest temperature at which life is possible is -17°C in an aqueous environment, as well as the remark that ‘‘the lowest temperature at which terrestrial and presumably martian life can function is probably near -20°C.’’ • Our data show no evidence of a threshold or cutoff in metabolic rate at temperatures down to -40°C. • A cell resists freezing, due to the ‘structured’ water in its cytoplasm • The absence of a threshold temperature for metabolism should encourage those interested in searches for life on cold extraterrestrial bodies such as Mars and Europa.
Ionizing-Radiation Resistance in the Desiccation-Tolerant Cyanobacterium Chroococcidiopsis
• In the four most resistant strains, the levels of survival were reduced by 1 or 2 orders of magnitude after irradiation with 5 kGy; viable cells were recovered after exposure to 15 kGy • The severe DNA damage evident after exposure to 2.5 kGy was repaired within 3 h, and the severe DNA damage evident after exposure to 5 kGy was repaired within 24 h.
Deinoccus radiodurans • Able to repair efficiently hundreds of DNA double- and single-strand breaks as well as other types of DNA damages promoted by ionizing or ultraviolet radiation • All basal DNA repair genes in IRRB, unlike many of their orthologs in IRSB, are subject to positive selection • D. radiodurans genome assumes an unusual toroidal morphology that may contribute to its radioresistance • Because of restricted diffusion within the tightly packed and laterally ordered DNA toroids, radiation-generated free DNA ends are held together, which may facilitate template-independent yet error-free joining of DNA breaks
Ionizing radiation on Mars • With a peak biologically-weighted dose rate of 0.85 Gy/year at no point is the ionizing radiation environment on or beneath the Martian surface lethal to even radiosensitive terrestrial bacteria. • Terrestrial species such as D. radiodurans can recover from doses four-orders of magnitude greater than this annual level with no detectable loss in viability • There is no reason Martian microbes might not have evolved even greater radioresistance.
A different paths of evolution on Mars • If there was abundant life on Mars at the beginning (likely), then continuous deterioration of the environment has exerted strong directional selection on that large population • Chance for the occurrence of advantageous mutations for a multiply extremophilic lifestyle was much higher than on Earth • Extremophiles on Earth can be suggestive, but lack of evidence is not the evidence of lack
Mi a legnagyobb probléma? • Egyelőre úgy néz ki, hogy Price ide vagy oda: túl hideg van! • Lehet, hogy csak potenciális, nem aktuális élőhely • Ha vannak ott élőlények, akkor is valószínűleg a rokonaink (nem független kísérlet) • Az Európa alighanem más tészta
Fisher’s (1930) question and “artificial life (AL)” "No practical biologist interested in sexual reproduction would be led to work out the detailed consequences experienced by organisms having three or more sexes; yet what else should he do if he wishes to understand why the sexes are, in fact, always two?"
Alternatív base pairs?
The combinatorics of hydrogen bond acceptors
binding
non binding
Benner’s (1990) extended genetic alphabet
C-C bond
Az RNS-világ
• RNS: genetikai anyag • RNS: enzim
The fitness of ribo-organisms W(N) = A(N) Q(N)
(cf. Eigen, 1971)
W
fitness
A
reproduction rate
Q
fidelity of replication
N
size of the alphabet
A négyféle bázis optimális lehetett az RNS világban • Mert már kellően hatékonyak lehettek a ribozimek • És mert még kellően pontos lehetett a replikáció • Evolúciós optimum • Tesztelhető hipotézis
