Subsample biosignature analyses. On selected subsamples, perform an array of high-sensitivity, mutually confirming laboratory investigations as described below.
The identity, abundance, and isomeric distribution of carbon compounds should be analyzed to low detection levels (parts per billion or below by weight within bulk ~100-mg subsamples) and to high molecular weights (hundreds to thousands of Daltons) at high peak resolutions. Mass spectrometry measurements should be configured to enable the detection of less volatile species that are relevant to the preservation of biosignatures. The isotopic ratios of C, H, N, O, P, and S should be characterized with sufficient precision to enable biogenic, environmental, or meteoritic fractionation trends to be identified. Compound-specific isotope analyses are highly desirable. Additional isotope ratios that further characterize atmospheric components and aqueous processes are also needed.
Highly sensitive tests for the presence and characteristics of specific biosignatures should be conducted on bulk subsamples or isolated extraction products (e.g., phases or concentrates). Biosignatures of particular interest include the identities or abundances of molecular compounds of distinctly biological origin as known on Earth, indicators of extant metabolic processes such as disequilibrium chemistry, and chemical or morphological traces of such compounds and processes preserved in minerals. Examples of specific tests include detection of amino and nucleic acids, lipids, and proteins; determination of chirality in amino acids and sugars; detection of enhanced concentrations of molecules that suggest selective use of specific isomers; and observations of cellular morphology or microfossils.
Instruments that can make the observations and measurements required for astrobiology are not generally at the technology readiness level necessary to allow their inclusion in Mars missions. New developments in instrumentation are being fueled by the medical industry and by concerns about biowarfare agent detection and should be incorporated into spacecraft mission planning. Examples of new technologies include the following:
Microelectromechanical systems. This technology takes advantage of new techniques for manufacturing miniaturized components, producing smaller, sensitive instruments for portable use.
Microelectro-optical systems. These optic systems would provide more capable imaging and spectroscopy.
Microfluidics. Sometimes called “lab on a chip,” these fluidic circuits when cut into a glass or plastic wafer can transport and mix fluids, bring dried reagents into contact with fluid to perform reactions, combine liquid with electrical currents for electrophoresis or sample concentration, and perform sensitive measurements on analytes of interest.
Imaging. Atomic-force microscopy is being used on both the Rosetta and the Phoenix missions. Currently it is the only way to image in space beyond the limitations of optical devices. Other imaging technologies including interferometry, scanning near-field optical microscopy, and electron microscopy techniques should also be developed for spaceflight applications.
Imaging spectroscopy. Coupling spectroscopy to imaging is an extremely powerful tool for elucidating the chemistry of any sample. An example relevant to astrobiology is the use of imaging-Raman systems detect reduced carbon in microfossils and in ALH 84001.4-7 The use of multiple/tunable laser systems, light-emitting diodes, and advances in miniaturization and detector design have direct relevance to spacecraft spectrometers.
Mass spectrometry. Mass spectrometry (MS) coupled to some form of gas chromatography (GC) system is the method of choice for unambiguous identification of organic molecules. The chromatography is essential to resolve and obtain the characteristic spectra of isobaric compounds and determine their relative abundances. Instruments used for Mars exploration would likely exploit the well-established technologies of electron impact ionization and quadrupole or time-of-flight (TOF) mass analyzers. Given the low expected abundances of organic molecules in Mars samples, attention should be paid to improving sensitivity over that of existing methodologies.
Biotechnology. Key technologies for life detection involve specific recognition of a target of interest using a probe molecule. A probe molecule is one that has a site that interacts specifically with the target, allowing its con-