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Life in the Cold

Life in the Cold. Neill Reid STScI & Maryland Astrobiology Consortium. Maryland Astrobiology Consortium. STScI Mark Clampin (GSFC) Mario Livio Steve Lubow Melissa McGrath (now Marshall) Keith Noll Antonella Nota Neill Reid Kailash Sahu Bill Sparks Jeff Valenti. COMB, UMD Bob Belas

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Life in the Cold

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  1. Life in the Cold Neill Reid STScI & Maryland Astrobiology Consortium

  2. Maryland Astrobiology Consortium STScI Mark Clampin (GSFC) Mario Livio Steve Lubow Melissa McGrath (now Marshall) Keith Noll Antonella Nota Neill Reid Kailash Sahu Bill Sparks Jeff Valenti COMB, UMD Bob Belas Rick Cavicchioli (Univ. NSW) Feng Chen Albert Colman Shil DasSarma Priya DasSarma Jochen Muller Frank Robb Kevin Sowers Hem Shukla

  3. Outline • Pushing the limits of the habitable zone • Cold environments on Earth • Cold environments in the Solar System • Environments of extrasolar planets • Terrestrial analogues for extraterrestrial life • Initial experimental results

  4. The classical habitable zone Definition: the circumstellar region where water can exist in liquid form on the surface of a planet. ~ 0.8 to 1.4 AU in the Solar System The habitable zone evolves as Lsun evolves  “continuous habitable zone” Can life survive and replicate beyond these limits?

  5. Terrestrial life in the cold We view Earth as a temperate environment, but 95% of the biosphere exists at T < 5oC  Recent investigations show evidence for extensive species diversity, notably at the microbial level

  6. The Solar System - Mars Mars lies beyond the current HZ, but probably still has substantial sub-surface water – and temperatures can rise above freezing Mars ain’t the kind of place to raise your kids In fact, it’s cold as hell….. B. Taupin Canyon gullies in Hellas

  7. The Solar System - Europa Europa lies at 5 AU from the Sun, well beyond the conventional habitable zone – but there is an alternative energy source: tidal heating by Jupiter.  Measurement of Europa’s magnetic moment strongly suggests the presence of an extensive sub-surface ocean beneath a moderately-thick (3-4 km?) icy crust.

  8. Extrasolar planets - statistics • 143 planets in 125 ‘normal’ planetary systems • 5 discovered in transit surveys • 1 by gravitational microlensing • 119 by radial velocity surveys • There are at least 15 multi-planet systems (indications of others from long-period trends) • Lowest mass planet: Gl 436b, M~0.067MJ or ~21ME – Neptunian-mass companion of a nearby M dwarf • Shortest period systems: P~1.2 days, a~0.015 AU • Longest period systems: P ~ 8 years, a ~ 4.2 AU

  9. Extrsolar planets - hosts Most stars with detected planets are similar to the Sun – Masses ~ 0.8 to 1.2 Msun Most are H-burning main sequence stars – some giants and 2 low-mass M dwarfs  Partly reflects bias in radial velocity surveys – we’re looking for planetary systems like our own (and solar type stars are good targets for Doppler surveys)

  10. Extrasolar planet environments • Planetary temperatures depend on: • Luminosity of central star • Distance from central star • Planetary atmosphere (albedo and greenhouse effect) • 1+2  substellar temperature • For Earth, TSS = 394K • equilibrium temperature: • Teq = 279 K, 6 oC • Many extrasolar planets have eccentric orbits, so Teq changes significantly over the planetary ‘year’

  11. Extrasolar planets - temperatures Teq scales with period, since most hosts are solar-type stars Average Teq ranges from ~1100oC for ‘hot Jupiters’ to -150oC for Jovian analogues; systems on eccentric orbits have significant annual variations.

  12. Extrasolar planets – habitable zones ~40 known planets spend part of their orbit within the habitable zone of their primary Over 10 planets are within the habitable zone for the most orbit – although most have high e and large T range. Best prospect (?): HD 28185, G5, 5.6 MJ planet in 1.0 AU orbit, e=0.06 -1 < T < 16oC Large gas giant – but what about satellites?

  13. Life at the extremes Archaeal and bacterial prokaryotic life supplies most of the biodiversity in extreme environments: High temperatures: thermophiles – growth at 40 to 80oC hyperthermophiles - growth at T > 80oC Room temperature: Mesophiles – optimal growth at 20 to 40oC Low temperatures: Psychrotrophs - optimal growth at T > 20oC, but can grow at temperatures between ~0 and 20oC Psychrophiles - optimal growth at T < 15oC

  14. Pushing life’s limits: psychrophiles as ET analogues Physiological adaptation to cold: • Accumulation of osmolytes (sugars, polyols, amino acids, inorganic ions) – protection against freezing • Alteration of lipids in membranes to give increased fluidity (e.g. higher proportion of unsaturated fatty acids) • Cold shock proteins • Metabolic activity relies on psychrophilic enzymes Questions: • What the low temperature limits for survival and growth? • How do individual species adapt genetically to low temperatures? • Is there commonality between species in adaptation to low temperatures?

  15. Test species • Halophiles: high salt tolerance • Halobacterium sp. NRC-1 – mesophile; genomesequenced • Halorubrum lacusprofundi – psychrotroph from Deep Lake, Antarctica; draft genome sequence • Methanogens: • Methanosarcina acetivorans – mesophile; genome sequenced • Methanococcoides burtonii – psychrophile from Ace Lake, Antarctica; draft genome sequenced • Control • Escherichia coli – mesophile; genome sequenced

  16. Experimental goals • Phase I: characterise life’s limits • culture individual species at temperatures T~10, 4, 0, -4oC • measure growth • Phase II: characterise genetic changes • for systems with sequenced genomes, use microarrays to identify genetic mutations • compare species for systematic changes with decreasing temperature

  17. Microarrays and genetic profiles Microarrays detect changes in mRNA (messenger RNA) levels DNA  mRNA  protein Given a sequenced genome, design array of probes that react to specific mRNA  map which proteins are expressed (which genes are active) in a given species & look for variations with changing environments Cold shock\ proteins  Signal intensities 15oC (“red channel”) Signal intensities 42oC (“green channel”) Microarray image

  18. Growth curves Psychrotroph: significant growth at T=0oC  lower than previous limit Mesophile: little or no growth at T=0oC H. lacusprofundi, psychrotroph: significant growth at T= -1oC  lower than previous limit

  19. Morphological cold adaptation? Both H. lacusprofundi and M. burtonii cells are dispersed at moderate temperatures, but cluster at low temperatures. This effect has also been observed in H. lacusprofundi at high temperatures. Why? Ancestral memories?

  20. High resolution imaging Electron microscope imaging ofHalorubrum lacusprofundiat T=0o C Thread-like structures: transfer of nutrients? maintaining structural integrity? imaging artefact?

  21. Summary and conclusions • Cold environments are common • on Earth • in the Solar system • among extrasolar planetary systemssystems • Life (particularly archaeal life) is abundant in terrestrial cold environments • We are conducting experiments designed to probe the low temperature limits for life and search for systematic genetic adaptation. Preliminary results: • extended low temperature growth limits for H. lacusprofundi and M. burtonii • evidence for a significant change in morphology at low temperatures

  22. Some species still prefer mesophilic environments…

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