The Importance of Sample Return in Establishing Chemical Evidence for Life on Mars or Elsewhere

Transcription

1 The Importance of Sample Return in Establishing Chemical Evidence for Life on Mars or Elsewhere D. P. Glavin, P. Conrad, J. Dworkin, J. Eigenbrode, and P. R. Mahaffy NASA Goddard Space Flight Center, Greenbelt MD Life in the Solar System and the Importance of Water The Woodlands, TX March 5, 2011 MSL Curiosity Sample Analysis at Mars (SAM) Mars Sample Return J.- L. Lacour (CEA)

2 Mars Exploration Program Science Goal GOAL I: DETERMINE IF LIFE EVER AROSE ON MARS (MEPAG, 2010) Is there life? Was there life? How long was there surface water? Where are the ORGANICS?

3 The Molecules of Life Dry weight composition of E. coli (Niedhardt, 1990) protein 57% RNA 21% DNA 3% lipids 9% amino acids nucleobases carboxylic acids other 10% Total 100% Ability to detect molecules relevant to life is important to understand past or present habitability of Mars

4 Did Viking Detect Organics? No organics of martian origin above the part per billion (ppb) level by pyrolysis GCMS, CH 3 Cl and CH 2 Cl 2 were detected (Biemann et al. 1977) Thermal modification or oxidation of organics during pyrolysis? Detection of perchlorates by Phoenix (Hecht et al. 2009) Martian organic carbon (up to ppm levels) converted to chlorohydrocarbons during Viking high temperature pyrolysis (Navarro-González et al. 2010) Even at ppb level, amino acids from >10 6 million cells per gram of Martian soil would not have been detected (Glavin et al. 2001) Thus, Viking did not necessarily rule out possibility of biology Shallow Martian permafrost (from Phoenix mission)

5 Preservation of Organics on Mars? Powerful surface oxidant? (Klein et al. 1979) Intense UV and ionizing radiation will destroy organics (Oro and Holzer, 1979; ten Kate et al. 2005; Garry et al. 2006) Decomposition of amino acids by ionizing radiation suggests shielding depths of >1-2 m required for preservation in ancient sediments Kminek and Bada, 2006; Parnell et al MSL does not have deep drilling capability, but organic preservation in overhangs or recently exposed outcrops still possible Organics? Clays have good organic preservation potential if deposited rapidly in an anoxic environment (Farmer and Des Marais, 1999; Michalski et al. 2010) Mawrth Vallis exposes layers with differing mineralogy, including Al- and Fe/Mg- rich phyllosilicates (Michalski et al and references therein)

6 2011 Mars Science Laboratory Curiosity s primary scien1fic goal is to explore and quan1ta1vely assess a local region on Mars surface as a poten1al habitat for life, past or present Key Science ObjecCves: 1. Assess the biological potencal, including preservacon of organic compounds 2. Characterize geology and geochemistry 3. InvesCgate the role of water, atmospheric evolucon 4. Characterize surface radiacon ANALYTICAL LABORATORY (ROVER BODY) SAM (P. Mahaffy, GSFC/CNES) - Chemical and isotopic composijon, including organics CheMin (D. Blake, ARC) - Mineralogy

7 Sample Analysis at Mars (SAM) Principal InvesCgator: Paul Mahaffy NASA Goddard Space Flight Center SAM Suite of 3 Instruments: Quadrupole Mass Spectrometer (QMS) Gas Chromatograph (GC) Tunable Laser Spectrometer (TLS) QMS: molecular and isotopic composijon in the Dalton mass range for atmospheric and evolved gas samples GC: resolves complex mixtures of organics into separate components TLS: abundance and isotopic composijon of CH 4, CO 2, and H 2 O Atmospheric Inlets Tunable Laser Spectrometer Electronics Quadrupole Mass Spectrometer SMS (74 cups) Gas Chromatograph Solid Sample Inlets Chemical Separation and Processing Laboratory Several advances from Viking GCMS: 1. Higher temperature pyrolysis (1000 C), evolved gas analysis mineral signatures 2. More sample cups (74 total) 3. Carbon isotopic measurements (TLS) 4.Low temperature chemical derivaczacon, targets key organic biomarkers, including amino acids and carboxylic acids

8 Mars Analog Studies Astrobiology Sample Analysis Program (ASAP): Established in 2007 with NASA Astrobiology Institute support ASAP Laboratory Analyses Participation from NASA GSFC, ARC, JPL, CIW, APL, LANL, UCB, UCSD, and IU 8 terrestrial analog samples and 1 meteorite were investigated ASAP Goals: 1) Compare MSL and ExoMars in situ flight instrumentation with state-of-the-art laboratory instrumentation Analog Samples: 2) Determine what the mineralogy, elemental abundances, organic and isotopic compositions, and life detection measurements tell us about habitability 3) Understand what additional Astrobiology science objectives could be met by a Mars sample return mission

9 SAM-like Pyrolysis GCMS Pyrolysis (up to 1100 C) and hydrocarbon trap Benzene (~9,700 ppb) LOD ~ 10 ppb QMS GC Relative Abundance Simple aromatics hydrocarbons and fragments of complex molecules, difficult to establish origin since these organics are also found in meteorites ~100 mg soil Atacama Desert, Chile Retention time (min)

10 SAM-like Derivatization GCMS SMS includes 9 metal cups containing derivatization solvent, lower temperature (< 300 C) extraction of organics SMS ~500 mg Valine (~ 10 ppb) Amino acids can be extracted using MTBSTFA and identified by GCMS; but difficult to establish biological origin since also found in meteorites

11 Standard Laboratory Amino Acid Analysis Standard Multi-Step Amino Acid Extraction and Analysis (~ 3 days): (1)Water extraction (100ºC 24h) (2) Acid hydrolysis (6 M HCl, 150ºC 3h) (3) Desalting (cation exchange) (4) Derivatization (OPA/NAC) (5) LC-FD/ToF-MS Analysis Amino Acid Atacama Desert Surface Soil MTBSTFA GCMS (ppb) LCMS (ppb) LCMS (D/L ratio) Asp Not detected Glu Not detected Ser Not detected Ala ~ Val ~ Gly ~ β-ala Not detected GABA Not detected ~100 mg Predominance of L-protein amino acids (low D/L ratios) indicates a biological origin. Total amino acid abundance corresponds to ~10 7 cells per gram Laboratory LC-FD/TOF-MS Fused silica blank

12 Recent success story: Detection of cometary glycine in STARDUST material Amino acids not detected in comets by remote observations or in situ measurements, although 20+ simple molecules have been observed (Crovisier et al. 2004) Aerogel Foil Stardust collected over 1000 particles (and volatiles) from comet Wild 2 and returned them to Earth in January 2006 ~5-10 mg aerogel fragments and several pieces of aluminum foil analyzed for amines at NASA Goddard Elsila, Glavin, Dworkin (2009) Glycine δ 13 C = +29 Carbon isotope ratio of Stardust glycine δ 13 C = +29 proves it is of extraterrestrial origin; terrestrial range: δ 13 C = -6 to -40 This measurement IS NOT possible with current spaceflight instrument technology! Gas Chromatograph Isotope Ratio Mass Spectrometer CH 3 OH HCN C 2 H 6 IRMS QMS GC Amino acids? H 2 NCH 2 COOH NH 3

13 MSL will carry out the first search for amino acids on Mars We may get very lucky and find indigenous amino acids (or other chemical biosignatures) preserved in ancient martian sediments However, ruling out a non-biological origin will require additional measurements that are beyond the capability of MSL, including: Some final thoughts. Enantiomeric measurements (chirality) Compound specific isotopic measurements Isotopic and molecular and spatial resolution Future missions (MAX-C and ExoMars) may provide additional information on the origin of any organic compounds on Mars Ultimately, a carefully selected sample from Mars will be required for a robust laboratory screening of chemical biomarkers and will enable new analytical approaches to search for life that would be very difficult, if not impossible to achieve on a robotic mission

14 Final thought.really this time Two Rovers to the Same Site on Mars, 2018: Possibilities for Cooperative Science Final Report of the Two Rover International Science Analysis Group (MEPAG 2R-iSAG, 2010) FINDING #1. The proposed ExoMars and MAX-C rovers have complementary capabilities. Most obviously, ExoMars would have vertical exploration capabilities via a drill not present on MAX-C, and MAX-C would have better horizontal mobility and rapid reconnaissance capabilities. This complementarity naturally lends itself to cooperative exploration and sample caching opportunities. Caching a subsurface sample acquired by ExoMars for return to Earth may provide the best chance for identifying chemical biosignatures on Mars.

15 Acknowledgments Funding for the analog research provided by the NASA Astrobiology Institute (NAI) DDF Program, and the NASA Mars Science Laboratory (MSL) and ESA ExoMars Projects We appreciate the Goddard Center for Astrobiology for continued support of ASAP and the SAM instrument team for helpful discussions J. Elsila, M. Martin, and F. Stalport for assistance with the derivatization and GCMS measurements We also thank M. S. Bell, J. Grotzinger, D. Ming, T. McCoy, C. McKay, K. Snook, L. Welzenbach, and the 2007 AMASE Team for providing the analog samples