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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

Resulting top-of-atmosphere spectral reflectivity of planets with surfaces dominated by the pigmented microbes described in Sections 2.3 and 3.1 and shown in Fig. 4. The microbe surfaces are modeled as diffuse reflectors. The average solar zenith angle is assumed to be 60°. The reflectivity is calculated as the modeled top-of-atmosphere spectral irradiance divided by the spectral irradiance of the Sun and not corrected for solar zenith angle. The dashed lines bracket the wavelength region containing the strongest feature seen in the measured reflectance spectrum (listed in Table 4). For the purpose of illustration, the spectra have been smoothed with a moving 5-point statistical mean.
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f5: Resulting top-of-atmosphere spectral reflectivity of planets with surfaces dominated by the pigmented microbes described in Sections 2.3 and 3.1 and shown in Fig. 4. The microbe surfaces are modeled as diffuse reflectors. The average solar zenith angle is assumed to be 60°. The reflectivity is calculated as the modeled top-of-atmosphere spectral irradiance divided by the spectral irradiance of the Sun and not corrected for solar zenith angle. The dashed lines bracket the wavelength region containing the strongest feature seen in the measured reflectance spectrum (listed in Table 4). For the purpose of illustration, the spectra have been smoothed with a moving 5-point statistical mean.

Mentions: Figure 5 shows the simulated spectral reflectivity (the top-of-atmosphere irradiance divided by the incident solar irradiance) for sunlight transmitted through an Earth-like atmosphere and reflected from surfaces that have the same diffuse spectral reflectance properties as the experimentally measured microbes. Dashed vertical lines indicate the wavelength region containing the strongest spectral feature in the experimental reflectance spectra. Table 5 lists the maximum fractional reflectivity change in the synthetic spectra over these wavelength regions by using Eq. 4. Because the spectra were generated assuming the average solar zenith angle for a planet observed at quadrature, the reflectivity given in Fig. 5 is not on the same absolute scale as the reflectance in Figs. 3 and 4.


Nonphotosynthetic pigments as potential biosignatures.

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

Resulting top-of-atmosphere spectral reflectivity of planets with surfaces dominated by the pigmented microbes described in Sections 2.3 and 3.1 and shown in Fig. 4. The microbe surfaces are modeled as diffuse reflectors. The average solar zenith angle is assumed to be 60°. The reflectivity is calculated as the modeled top-of-atmosphere spectral irradiance divided by the spectral irradiance of the Sun and not corrected for solar zenith angle. The dashed lines bracket the wavelength region containing the strongest feature seen in the measured reflectance spectrum (listed in Table 4). For the purpose of illustration, the spectra have been smoothed with a moving 5-point statistical mean.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f5: Resulting top-of-atmosphere spectral reflectivity of planets with surfaces dominated by the pigmented microbes described in Sections 2.3 and 3.1 and shown in Fig. 4. The microbe surfaces are modeled as diffuse reflectors. The average solar zenith angle is assumed to be 60°. The reflectivity is calculated as the modeled top-of-atmosphere spectral irradiance divided by the spectral irradiance of the Sun and not corrected for solar zenith angle. The dashed lines bracket the wavelength region containing the strongest feature seen in the measured reflectance spectrum (listed in Table 4). For the purpose of illustration, the spectra have been smoothed with a moving 5-point statistical mean.
Mentions: Figure 5 shows the simulated spectral reflectivity (the top-of-atmosphere irradiance divided by the incident solar irradiance) for sunlight transmitted through an Earth-like atmosphere and reflected from surfaces that have the same diffuse spectral reflectance properties as the experimentally measured microbes. Dashed vertical lines indicate the wavelength region containing the strongest spectral feature in the experimental reflectance spectra. Table 5 lists the maximum fractional reflectivity change in the synthetic spectra over these wavelength regions by using Eq. 4. Because the spectra were generated assuming the average solar zenith angle for a planet observed at quadrature, the reflectivity given in Fig. 5 is not on the same absolute scale as the reflectance in Figs. 3 and 4.

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