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Nonphotosynthetic pigments as potential biosignatures.

Schwieterman EW, Cockell CS, Meadows VS - Astrobiology (2015)

Bottom Line: We present an interdisciplinary study of the diversity and detectability of nonphotosynthetic pigments as biosignatures, which includes a description of environments that host nonphotosynthetic biologically pigmented surfaces, and a lab-based experimental analysis of the spectral and broadband color diversity of pigmented organisms on Earth.We test the utility of broadband color to distinguish between Earth-like planets with significant coverage of nonphotosynthetic pigments and those with photosynthetic or nonbiological surfaces, using both 1-D and 3-D spectral models.We demonstrate that, given sufficient surface coverage, nonphotosynthetic pigments could significantly impact the disk-averaged spectrum of a planet.

View Article: PubMed Central - PubMed

Affiliation: 1University of Washington Astronomy Department, Seattle, Washington, USA.

ABSTRACT
Previous work on possible surface reflectance biosignatures for Earth-like planets has typically focused on analogues to spectral features produced by photosynthetic organisms on Earth, such as the vegetation red edge. Although oxygenic photosynthesis, facilitated by pigments evolved to capture photons, is the dominant metabolism on our planet, pigmentation has evolved for multiple purposes to adapt organisms to their environment. We present an interdisciplinary study of the diversity and detectability of nonphotosynthetic pigments as biosignatures, which includes a description of environments that host nonphotosynthetic biologically pigmented surfaces, and a lab-based experimental analysis of the spectral and broadband color diversity of pigmented organisms on Earth. We test the utility of broadband color to distinguish between Earth-like planets with significant coverage of nonphotosynthetic pigments and those with photosynthetic or nonbiological surfaces, using both 1-D and 3-D spectral models. We demonstrate that, given sufficient surface coverage, nonphotosynthetic pigments could significantly impact the disk-averaged spectrum of a planet. However, we find that due to the possible diversity of organisms and environments, and the confounding effects of the atmosphere and clouds, determination of substantial coverage by biologically produced pigments would be difficult with broadband colors alone and would likely require spectrally resolved data.

No MeSH data available.


Related in: MedlinePlus

Color-color plot comparing the normalized colors of lifeless surfaces (squares), pigmented biological surfaces (circles), these surfaces under an Earth-like cloudless atmosphere (diamonds), and two cases that are diurnal averages of a heterogeneous planet with realistic clouds (asterisks). Each set is color-coded in the figure legend. Arrows are drawn from the colors with no radiative effects from the atmosphere included, to the colors including effects from the atmosphere.
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f11: Color-color plot comparing the normalized colors of lifeless surfaces (squares), pigmented biological surfaces (circles), these surfaces under an Earth-like cloudless atmosphere (diamonds), and two cases that are diurnal averages of a heterogeneous planet with realistic clouds (asterisks). Each set is color-coded in the figure legend. Arrows are drawn from the colors with no radiative effects from the atmosphere included, to the colors including effects from the atmosphere.

Mentions: Figure 11 shows the broadband colors of abiotic and biological surfaces from the USGS and ASTER spectral libraries, and colors resulting from the normalized spectral reflectivities or albedos of the 1-D and 3-D spectral models. The colors of the 1-D (no clouds) and 3-D (heterogeneous surface and clouds) model spectra include the effects of scattering and absorption in the atmosphere, while the two 3-D model spectral colors additionally include the effects of realistic clouds. As expected, the effect of Rayleigh scattering makes the colors of the clear-sky spectra almost uniformly bluer. Red algae water, basaltic loam, and trees, apparent outliers when considering only the surface reflectance function in the color calculation, begin to populate similar areas in B*-V* versus B*-I* color space when the effects of scattering in a planetary atmosphere are included. The presence of an atmosphere therefore reduces the spread in the distribution of surface colors. This is consistent with work by Sanromá et al., (2013), who included fewer surface types in their analysis but noted a similar trend. For the two cases where heterogeneous surface distributions are assumed and cloud cover is included, that is, the ocean-dominated realistic Earth case and the halophile-dominated oceans case, colors are redder than the 1-D clear-sky cases but still bluer than seen for the airless, pure surface spectra cases. This reddening in comparison to the clear-sky cases is due to the effects of clouds, which truncate the atmospheric column, thereby decreasing Rayleigh scattering, while also behaving as gray scatterers.


Nonphotosynthetic pigments as potential biosignatures.

Schwieterman EW, Cockell CS, Meadows VS - Astrobiology (2015)

Color-color plot comparing the normalized colors of lifeless surfaces (squares), pigmented biological surfaces (circles), these surfaces under an Earth-like cloudless atmosphere (diamonds), and two cases that are diurnal averages of a heterogeneous planet with realistic clouds (asterisks). Each set is color-coded in the figure legend. Arrows are drawn from the colors with no radiative effects from the atmosphere included, to the colors including effects from the atmosphere.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4442567&req=5

f11: Color-color plot comparing the normalized colors of lifeless surfaces (squares), pigmented biological surfaces (circles), these surfaces under an Earth-like cloudless atmosphere (diamonds), and two cases that are diurnal averages of a heterogeneous planet with realistic clouds (asterisks). Each set is color-coded in the figure legend. Arrows are drawn from the colors with no radiative effects from the atmosphere included, to the colors including effects from the atmosphere.
Mentions: Figure 11 shows the broadband colors of abiotic and biological surfaces from the USGS and ASTER spectral libraries, and colors resulting from the normalized spectral reflectivities or albedos of the 1-D and 3-D spectral models. The colors of the 1-D (no clouds) and 3-D (heterogeneous surface and clouds) model spectra include the effects of scattering and absorption in the atmosphere, while the two 3-D model spectral colors additionally include the effects of realistic clouds. As expected, the effect of Rayleigh scattering makes the colors of the clear-sky spectra almost uniformly bluer. Red algae water, basaltic loam, and trees, apparent outliers when considering only the surface reflectance function in the color calculation, begin to populate similar areas in B*-V* versus B*-I* color space when the effects of scattering in a planetary atmosphere are included. The presence of an atmosphere therefore reduces the spread in the distribution of surface colors. This is consistent with work by Sanromá et al., (2013), who included fewer surface types in their analysis but noted a similar trend. For the two cases where heterogeneous surface distributions are assumed and cloud cover is included, that is, the ocean-dominated realistic Earth case and the halophile-dominated oceans case, colors are redder than the 1-D clear-sky cases but still bluer than seen for the airless, pure surface spectra cases. This reddening in comparison to the clear-sky cases is due to the effects of clouds, which truncate the atmospheric column, thereby decreasing Rayleigh scattering, while also behaving as gray scatterers.

Bottom Line: We present an interdisciplinary study of the diversity and detectability of nonphotosynthetic pigments as biosignatures, which includes a description of environments that host nonphotosynthetic biologically pigmented surfaces, and a lab-based experimental analysis of the spectral and broadband color diversity of pigmented organisms on Earth.We test the utility of broadband color to distinguish between Earth-like planets with significant coverage of nonphotosynthetic pigments and those with photosynthetic or nonbiological surfaces, using both 1-D and 3-D spectral models.We demonstrate that, given sufficient surface coverage, nonphotosynthetic pigments could significantly impact the disk-averaged spectrum of a planet.

View Article: PubMed Central - PubMed

Affiliation: 1University of Washington Astronomy Department, Seattle, Washington, USA.

ABSTRACT
Previous work on possible surface reflectance biosignatures for Earth-like planets has typically focused on analogues to spectral features produced by photosynthetic organisms on Earth, such as the vegetation red edge. Although oxygenic photosynthesis, facilitated by pigments evolved to capture photons, is the dominant metabolism on our planet, pigmentation has evolved for multiple purposes to adapt organisms to their environment. We present an interdisciplinary study of the diversity and detectability of nonphotosynthetic pigments as biosignatures, which includes a description of environments that host nonphotosynthetic biologically pigmented surfaces, and a lab-based experimental analysis of the spectral and broadband color diversity of pigmented organisms on Earth. We test the utility of broadband color to distinguish between Earth-like planets with significant coverage of nonphotosynthetic pigments and those with photosynthetic or nonbiological surfaces, using both 1-D and 3-D spectral models. We demonstrate that, given sufficient surface coverage, nonphotosynthetic pigments could significantly impact the disk-averaged spectrum of a planet. However, we find that due to the possible diversity of organisms and environments, and the confounding effects of the atmosphere and clouds, determination of substantial coverage by biologically produced pigments would be difficult with broadband colors alone and would likely require spectrally resolved data.

No MeSH data available.


Related in: MedlinePlus