Martian Life

The Case for Microbial Life on Mars

Overview 1. Timeline 2. Is life possible on Mars? 3. The Martian Environment 4. Introducing … the Extremophiles 5. Importance

Timeline • 1609 – Galileo • first to telescopically view Mars Galileo

• 1781 – William Herschel (British) • claims that Martian polar caps made of ice • 1784 to British Royal Society: Mars has a considerable but modest atmosphere, so that its inhabitants probably enjoy a situation in many respects similar to our own.

• 1854 – William Whewell

Herschel

• posits that Mars may harbor life

• 1877 – Giovanni Schiaparelli (Italian) • observation of canali

• 1895 – Percival Lowell (American) • claims canals were made by ancient civilization (Mars) W.O.T.W.

• 1897 – H.G. Wells • writes The War of the Worlds

Lowell

Timeline – The Modern Age • 1938 - Orson Welles • Mercury Theater on the Air

• 1965 – Mariner 4 • flyby of Mars reveals atmosphere Welles

• 1976 – Viking 1 • 1976 – Viking 2

Mariner 4

• 1997 – Mars Global Surveyor • 1997 – Mars Pathfinder • 2001 – Odyssey • 2004 – Spirit (Mars Exploration Rover A) • 2004 – Opportunity (Mars Exploration Rover B) • 2006 – Mars Reconnaissance Orbiter • 2008 – Phoenix Mars Lander (Scout Program) • Search for environments suitable for microbial life

Viking Program • Mariner missions (refocus search for life)

• Viking (Lander & Orbiter) • Viking 1 (1976-1982) • Viking 2 (1976-1980) • Biological Experiments • • • • •

Martian soil GC◦MS GEx (Gas Exchange) LR (Labeled Release) PR (Pyrolytic Release)

The Mars Viking Lander

• Orbiter • Surface imaging Viking Orbiter

Viking Program & Martian Life Assumptions about “Martians”

• Photosynthetic – Light & CO2 – Respiration

• Surface – < 5cm depth

• Earth-like

Ciccarelli et al. 2006. Science. 311: 1283

Viking Biological Experiments • Pyrolytic Release Experiment • Production of organics from CO2 • Not reproducible

• Labeled Release Experiment • Rapid release of CO2 in presence of nutrient solution • Followed by a prolonged, slow release • 160°C loss of activity • 40-60°C partial loss of activity • 18°C relatively stable (lost during long term storage)

• Gas Exchange • Soil release of O2 in presence of water • Evolution of CO2 in presence of nutrient solution

• GC◦MS

• Negative for organic compounds • WTF???

• Orbiter • “clear evidence that liquid water flowed on the surface of Mars in the past” (McKay, 1996)

Phoenix Mars Lander • • • •

Search for microbial life “Follow the water” 07/31/08 - Presence of water confirmed Wet Chemistry • • • •

Soil pH 8 to 9 Mg, Na, K, Cl present Carbonate identified (water interactions) Perchlorate also identified

• Detected atmospheric snow

The Martian Environment Mars Ionizing Radiation / hour ~10 REM

Earth negligible

Length of Day

24h 37m

23h 56m

Gravity

0.377g

1.0g

Atmosphere

95% CO2 2.7% N2 0.1% O2

78.1% N2 20.9% O2 0.03% CO2

Pressure

560 Pa

105 Pa

Avg. Surface Temp

-65°C

15°C

Diurnal Temp. Range

-89°C to -31°C

10°C to 20°C

Horneck, G. 2008. Acta Astronautica 63:1015-24

Is Life Feasible on Mars?

Meteorite fragment ALH 84001

Streptococcus

~20-100 nanometers

~600 nanometers

The Extremophiles Organisms that thrive in, and may even require, environmental conditions (physical and/or geochemically extreme) that are detrimental to the majority of life on Earth. Examples: Acidophiles – pH conditions under 3 Alkaliphiles – pH conditions over 9 Halophiles – Salt (NaCl) concentrations over 2M Psychrophiles – Temperatures under 15°C Radioresistant – Ionizing Radiation Thermophiles – Temperatures over 60°C Xerophiles – Arid conditions (desiccation)

The Xerophiles • Greek - xeros (dry) + philos (love) • Low water availability (water activity) • Arid conditions • deserts • ~1/3 of Earth’s surface • includes Antarctica

Deinococcus radiodurans

Cacti (a xerophile)

The Halophiles • Greek – halo (salt) + philos (love) • Domains: Archaea, Bacteria, and Eukarya • 2M salt concentration • Molarity of seawater ~0.5M

• Modes of Action: • Osmoprotectants “compatible solutes” • Potassium influx • Forces water towards proteins

• Dead Sea • Great Salt Lake

Great Salt Lake Halophilic Bloom

The Halophiles (con’t) • Halobacterium salinarum (4 to 5.5M [salt]) • Archaea • Two strains sequenced • NRC-1 • R1

• Halocins • Antimicrobial peptides/proteins

• Astrobiology candidate? • Form a salt crust • ↓ UV sensitivity Halobacterium sp. NRC-1

The Psychrophiles • Greek – psychro (cold) + philos (love) • Obligate (20 °C and lower) • Facultative (growth down to ~ 0 °C)

• Virtually Ubiquitous • • • • •

Alpine & arctic soils Antarctica (-20 °C mean) Deep Ocean Glaciers & snowfields permafrost

Desulfofrigus oceanense

Psychrophiles (con’t) • Modes of Action • Cryoprotectants (antifreeze) • Cellular adaptations (proteins, fatty acids) • Cold sensing Æ gene expression • Cold shock

• Exopolymers • Primarily polysaccharides

• Growth rate

The Alkaliphiles • Alkaline environments – pH > 9 (through 11)

• Mode of Action • Maintain pH of ~8 inside cells (proton pumps)

• Playa lakes, carbonate rich soils • Examples • Geoalkalibacter ferrihydriticus • Bacillus okhensis • Alkalibacterium iburiense

The Alkaliphiles (con’t) • Carbonate environments • Examples • Mono Lake • Octopus Spring (YNP)

“Tufa Towers” at Mono Lake

Wish You Were Here Pink Floyd

Radioresistance Short Term Dosages (Humans) 0-5 REM – Safe 50-100 REM – Anemia 100-200 REM – Nausea & fatigue 300-500 REM – LD50 500-1200 REM – Death in days >10,000 REM – Death in hours

Deinococcus radiodurans Lethal dose (37%) -15,000,000 REM

Radioresistance (con’t) • Other radioresistant bacteria • Thermococcus gammatolerans • Rubrobacter sp. • Chroococcidiopsis sp.

• Modes of Action • Multiple genome copies • Rapid DNA repair systems • Mn accumulation (?)

Rubrobacter

• Why? • Most likely to survive desiccation from arid environments (see Xerophiles)

So … where’s Waldo? • Surface conditions too harsh • Confirmed by Viking and Mars Lander

• “Martian oases” • Sub-surface is best bet • How deep? 50 cm, 1 m, 2 m, deeper? • 1 meter • • • •

dramatic drop (60-97%) in cosmic radiation Presence of liquid water (?) Lower temperature fluctuations (?) Geothermal activity (?)

Why Does It Matter? • Contamination of Mars • “Forward-contamination” • COSPAR • Committee on Space Research • Planetary protection concept • Decontamination of all equipment sent to Mars

• protect any possible Martian life

• Martian microbes? • harmful to human explorers? • brought back to Earth? (panspermia)

Forward Contamination Panspermia and

Forward-Contamination Contamination of other planets with microbes of Earth origin

Panspermia Contamination of Earth with microbes of an extraterrestrial origin

Further Reading •

McKay, C.P. 1997. The Search for Life on Mars. Origins of Life and Evolution of the Biosphere. 27: 263-89.

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Horneck, G. 2008. The Microbial Case for Mars and its Implication for Human Expeditions to Mars. Acta Astronautica. 63: 1015-24.

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DasSarma, S. 2006. Extreme Halophiles are Models for Astrobiology. Microbe. 1: 120-6.

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Klein, H.P., et al. 1976. The Viking Mission Search for Life on Mars. Nature. 262: 24-27.

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McKay, D.S., et al. 1996. Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001. Science. 273: 924-930 .