TABLE 5.2 Techniques Used to Measure Biosignatures

Biosignature and Technique

Measurement for Life Detection


Limitations and Developments Needed

Workshop Paper by


Spectroscopy (TPF)

Spectral lines in planetary atmospheres of extrasolar planets

Oxygen: 1% of Earth atmosphere; other gases to be determined

Imaging interferometry needs technical development


Macroscopic imaging systems (e.g., Galileo's Solid State Imager)

Morphology of macroscopic life and ecosystems

Less than ~10-m spatial resolution

Solar system objects only



Light microscopy

Structure; evidence for viability (motility, biofilms); noninvasive

0.2-µm spatial resolution

Morphology only; no chemistry

Electron microscopy (environmental SEM [ESEM], SEM, EDX)

High-resolution morphology and chemical composition (ESEM is noninvasive)

1-10 nm, 0.2 keV, 1% relative abundance

Requires contamination-free microscopes

Barker and Banfield

Electron microscopy (TEM, SAED, EELS)

Structure, redox state, mineralogy; invasive

1 nm, 0.2 keV, 1% relative abundance

Invasive sample preparation

X- ray microscopy

Electronic state of molecules

Nanometer resolution

Requires sectioning


Fluorescence microscopy

Structure; detect very small entities, macromolecules (nucleic acids and proteins); identify organisms (16S and 18S rRNA) and possibly viability number of ribosomes; mRNA)

Can be used to enumerate viruses (30- 50 nm)

Better preparation methods needed with rock and soil samples; at present time need to dislodge organisms for FISH

Stahl, D. McKay, Jacobsen, Cady

CT scan- XAFS imaging

Internal structure; noninvasive

Millimeters to centimeters

Higher spatial resolution needed



Structure and abundance of elements

1-10 nm, 0.2 keV, 1% relative abundance

Reduce diameter of EDX beam (<200 nm)

Barker and Banfield, Kirschvink

Ion and electron microprobes

Chemical and isotopic composition

Single organic molecules

D. McKay

Light microscopy, optical broadband spectroscopy

Chemical composition; noninvasive

0.2-µm spatial resolution

Limitations in spatial resolution

Jacobsen, Cady, D. McKay

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