where next in the search for life on mars? chris mckay nasa ames research center...
TRANSCRIPT
Where Next in the Search for Life on Mars?
Chris McKayNASA Ames Research Center
JHU, 9 April 2010
Ans: Ice
1. On a dry cold world, ice can be a source of liquid water.(Go to the North Polar Region of Mars)Follow Phoenix!
2. Ancient ice can preserve evidence of past life.(Go to the South Polar Region of Mars)
The Astrobiology Strategy(NRC report 2007)
follow the water
- search for organics
- characterize to detect signs of life
- return to Earth for analysis
Why do we search for a second genesis of life on other worlds?
Aliens: not on our tree of life
comparative biochemistry (life 2.0)
life is common in the universe (yeah!)
Phoenix Mission to Mars May 2008 to Nov 2008
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
5 Myr ago: 2x summer insolation
Murray et al. 1973Laskar et al. 2002
| surface melting| cold deep ice
The North Pole of Mars could have had liquid water 5 Myr ago
• Ice at the surface• Low elevationPressures >6.1 mbar
allows water to be stable• Summer Temperatures < 0oC now
but may be > 0oC at higher obliquity 5 million years ago.Liquid water on
Mars requires1. Ice2. T > 0ºC3. P> 6.1 mb
Unexpected Phoenix results
Soil pH ~8
Carbonates 3-5%
Perchlorate 0.5%
Segregated ice No organics
No nitrates } Instrument failures
bleachsalt
Perchlorates on Mars
• Perhclorates decomposeand release oxygen whenheated to ~350ºC- used in rockets- destroys organics
• Strong anti-freeze (-70ºC)- allow liquid on Mars today
• Consumed by microorganisms- terminal electron acceptor ≈ nitrate
Organics on Mars
•Everything we thought we knew about organics on Mars from the Viking pyrolysis GCMS is wrong
•The upper limit is not ppb, but 0.1% (a factor of a million correction)
Good news for future missions: organics might be high.
Bad news for future missions: need non-thermal methods
SAM will wash the samples with a derivatization agent:N-Methyl-N-(Tert-Butyldimethylsilyl) trifluoroacetamide and this mode should be free of perchlorate.
There is a pyrolysis GCMS on the upcoming MSL mission
Sample Analysis for Mars
Laser desorption mass spectromter. Part of Luann Becker’s (JHU) MOMA instrument for the ExoMars mission.
Mass specLaser
A simple approach to searching for organics in high perchlorate soil.
Is there life in places on Earth with ice like this?
Metabolism in permafrost down to -15oCLimited by nutrient transport - not temperature(Rivkina et al. Metabolic activity of permafrost bacteria below the freezing point, Appl. Environ. Microbio., 66, 3230-3233, 2000)
Rivkina et al. 2000
The rapid growth rate phase is limited by temperature.
Microorganisms in permafrost at -10oC are inactive.
Not because theyare cold but because they are have access only to thin films ofwater
Dry permafrost
• Ice cemented ground beneath dry permafrost that is always below -10ºC is habitable(consistent with Rivkina et al. 2000)
• In the dry permafrost of the dry valleys of Antarctica we find aerobic heterotrophs consuming organic material ultimately produced by cryptoendoliths in the sandstone
Antarctic site:dry permafrost over deep ground ice
35 cm
+1ºC
-10ºC
dry soil
ice & soil
Mars site:dry permafrost over ground ice
-30ºC
-50ºC
dry soil
ice & soil
salts
-5ºC
-15ºC
dry soil
ice & soil
5 Myr ago
Energy for life
• Antarctica:
organic material + O2
Energy for life
• Antarctica:
organic material + O2
• Mars:
basalt rocks (Fe++) + ClO4
Nealson, K. (2003) Nature Biotechnology 21, 243-244.
Perchlorate
Perchlorate could be an electron acceptor for a redox couple that supports life on Mars.
Habitability of the Phoenix site 5 Myr ago
• Carbon as CO2
• Liquid water
• Energy
• Nitrogen ? (nitrates in the soil??)
Nitrates on Mars Manning et al. Icarus, 2008
nitrate formation duringAccretion shocks
nitrate decomposition by impacts
N2 + CO2 NOx
NO3 N2 + O2
3 m of nitrate in the soil
Gilichinsky et al. 2007
Limits on long term dormancy
• kT: Thermal decay: ~e-E/kT
racemization of amino acidsdegradation of organic materialnot important on Mars, -70oC
• eV: Radiation from crustal U,Th, K ~0.2rad/yrlethal dose for Deinococcus radiodurans in 100 Myron Mars hundreds of lethal dose over 3.5 Gyr
• Its dead, Jim
If we find organic material in a frozen sample on Mars.
Can we tell if it was ever alive?
If its like us (DNA)then is easy, but less interesting
If its alien then hard, but interesting
Abiotic distributions are smoothBiotic distributions are spiked
McKay 2004 PLoS Biol 2(9)1260-12623
Abiotic distributions are smoothBiotic distributions are spiked
McKay 2004 PLoS Biol 2(9)1260-12623
alien
