NASA Astrobiology Institute (NAI)

1. Design, construction and testing of a Cavity-Ring Down Spectrometer for determination of the concentration and isotopic composition of methane

   Project Investigators: John Kessler, Tullis Onstott

   Other Project Members

   Barbara Sherwood Lollar (Collaborator)

   Summary

   The recent detection of CH₄ in the Martian atmosphere and observations suggesting that it varies both temporally and spatially argues for dynamic sources and sinks. CH₄ is a gaseous biomarker on Earth that is readily associated with methanogens when its H and C isotopic composition falls within a certain range. It is imperative that a portable instrument be developed that is capable of measuring the C and H isotopic composition of CH₄ at levels comparable to that on Mars with a precision similar to that of an isotope ratio mass spectrometer and that such an instrument be space flight capable. Such an instrument could guide a rover to a site on Mars where emission of biogenic gases is occurring and samples could be collected for Mars sample return.

   Astrobiology Roadmap Objectives:

   • Objective 2.1: Mars exploration
   • Objective 2.2: Outer Solar System exploration
   • Objective 3.3: Origins of energy transduction
   • Objective 4.1: Earth's early biosphere
   • Objective 5.1: Environment-dependent, molecular evolution in microorganisms
   • Objective 5.2: Co-evolution of microbial communities
   • Objective 5.3: Biochemical adaptation to extreme environments
   • Objective 6.1: Environmental changes and the cycling of elements by the biota, communities, and ecosystems
   • Objective 6.2: Adaptation and evolution of life beyond Earth
   • Objective 7.1: Biosignatures to be sought in Solar System materials
   • Objective 7.2: Biosignatures to be sought in nearby planetary systems

   Project Progress

   Design, construction and testing of a Cavity-Ring Down Spectrometer (CRDS) for determination of the concentration and isotopic composition of methane

   During the past 12 months, we have measured in detail the absorption spectra for ¹²CH₄, ¹³CH₄, CH₃D and CO₂. We’ve designed a peak fitting routine to integrate the ¹²CH₄ and ¹³CH₄ peaks in the wavelength region of our CRDS. We’ve tested this software on a CH₄ gas standard of known isotopic composition and were able to reproduce the δ¹³C of the 2 ppm standard with an accuracy of ±5o/oo. Although this accuracy is twice that of the multipass instrument on MSL, it is 10 times less than the accuracy of the individual ring-down events. The inaccuracy is due to imprecision in the wavelength of the laser, which will be rectified by upgrading the instrument with a wavelength monitor. A manuscript describing the methodology, instrument and first measurement is being prepared for Optics Express. A proposal to take the current instrument to Technology Readiness Level 6 was submitted to the Mars Instrument Development Program in June ’07 with collaboration from Paul Mahaffy of Goddard Space Flight Center and has recently been awarded.

   We also tested a Los Gatos CRDS at the McGill University arctic research station (MARS) on Axel Heiberg Island for two weeks in April ’08 where we measured CH₄ fluxes from the permafrost soil and hot springs. These results indicate that the CH₄ fluxes are sufficiently high that our current CRDS should be able to measure their isotopic composition and our current plan is to return to MARS next spring with the upgraded instrument. We are presently preparing the instrument for CH₄ activity measurements on permafrost methanogens while they are being exposed to simulated Martian conditions at the Techshot facility in Greenfield, Indiana.

   Mission Involvement

   MFL

   A Cavity Ringdown Spectrometer is the instrument most likely to be ready for the next landed instrument package on Mars after the Mars Science Laboratory. Onstott and Mahaffy (Goddard) will collaborate on development of an improved Cavity Ringdown Spectrometer with funding from a recent NASA MDIP award.

   Cross-Team Collaborations

   Paul Mahaffy at Goddard has been collaborating with Onstott and Kessler on calibration of a Cavity Ringdown Spectrometer. Mahaffy and Onstott will now design and build an improved spectrometer with funding from a NASA MDIP.

Publications

Kessler, J.D.  (2008).  Isotopic Characterization of Martian Methane by CRDS.  AbSciCon.  Santa Clara CA.