Extremities:  Geology and Life in Yellowstone and Implications for Other Worlds


Reflectance Spectroscopy is measuring the proportion of light that reflects off objects as a function of the light's wavelength. Reflectance spectroscopy is one of several methods NASA uses to try to detect Mars life from orbit. We measured the reflectance spectra of the microbial mats we collected, both to see how the microbes use the light, and to see how they could be detected. We used the ALTA spectrometer, invented by Allan Treiman. Using the ALTA, we measured the proportion of light reflected by the mats in eleven different wavelenthts of light, from blue (470 nm) through red (700 nm) through near-infrared (980 nm).

ALTA Spectrometer



The ALTA spectrometer: twelve buttons for twelve LED lamps in twelve different wavelengths, ranging from blue through red through near infrared (NOT thermal infrared).


The ALTA spectrometer in use by 5th grade GT students in Texas. There are no pictures of our group using them to take reflectance spectra of microbial mats (the photographer was otherwise distracted).




Octopus Spring Mats



Octopus Spring microbial mats and their reflectance spectra (credits). The dishes hold the top half (green) and bottom half (pink) of the sample we collected. The bottom half of the mat, (the upper, red line) is mostly the green non-sulfur bacterium Chloroflexus. [Even though it is not green, that's still its classification.] It refelcts the least light near 850 - 900 nm, which represents the maximum light absorption of its bacteriochlorophyll a.



Nicer graph with spectra of the green mat top and pink mat bottom (credits). Tops 1 and 2 show the same absorptions, although 1 is paler (higher reflectance) than 2. The mat top is mostly Synechococcus, a blue-green 'alga,' which contains chlorophyll a. It absorbs little light between about 750 and 900 nm, which penetrates through to the pink Chloroflexus layer.

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