Where Next in the Search for Life on Mars? Chris McKay NASA 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) 4 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

5 Myr ago: 2x summer insolation Murray et al Laskar et al | surface melting| cold deep ice

The North Pole of Mars could have had liquid water 5 Myr ago Ice at the surface Low elevation  Pressures >6.1 mbar allows water to be stable Summer Temperatures 0 o C at higher obliquity 5 million years ago. Liquid water on Mars requires 1.Ice 2.T > 0ºC 3.P> 6.1 mb

Unexpected Phoenix results Soil pH ~8 Carbonates 3-5% Perchlorate 0.5% Segregated ice  No organics No nitrates } Instrument failures

bleach salt

Perchlorates on Mars Perhclorates decompose and release oxygen when heated 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 spec Laser 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 -15 o C Limited by nutrient transport - not temperature (Rivkina et al. Metabolic activity of permafrost bacteria below the freezing point, Appl. Environ. Microbio., 66, , 2000)

Rivkina et al The rapid growth rate phase is limited by temperature.

Microorganisms in permafrost at -10 o C are inactive. Not because they are cold but because they are have access only to thin films of water

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 + O 2

Energy for life Antarctica: organic material + O 2 Mars: basalt rocks (Fe ++ ) + ClO 4

Nealson, K. (2003) Nature Biotechnology 21, 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 CO 2  Liquid water  Energy  Nitrogen ? (nitrates in the soil??)

Nitrates on Mars Manning et al. Icarus, 2008 nitrate formation during Accretion shocks nitrate decomposition by impacts N 2 + CO 2  NOx NO 3  N 2 + O 2 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 acids degradation of organic material not important on Mars, -70 o C eV: Radiation from crustal U,Th, K ~0.2rad/yr lethal dose for Deinococcus radiodurans in 100 Myr on 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 smooth Biotic distributions are spiked McKay 2004 PLoS Biol 2(9)

Abiotic distributions are smooth Biotic distributions are spiked McKay 2004 PLoS Biol 2(9) alien