Biosignatures & Paleobiology

Photosynthetic Fluorescence From Earth-Like Planets Around Sun-Like Aand Cool Stars

By Keith Cowing
Press Release
January 11, 2023
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Photosynthetic Fluorescence From Earth-Like Planets Around Sun-Like Aand Cool Stars
Simulated spectrum with the biological fluorescence on a second Earth around a Sun-like star at 10 pc from the Earth, assuming a LUVOIR-A-like space telescope. (a–c) The results from the veg-only 0B model and (d) Fp/Fs with the veg-land 0B model. (a) Fp/Fs with 9000 hours of observation time. The solid line shows Fp/Fs and the error bar indicates the noise at each wavelength. (b) A magnification of Fp/Fs in (a). (c) The SNR in (a). — astro-ph.EP

Remote sensing of the Earth has demonstrated that photosynthesis is traceable as the vegetation red edge (VRE), which is the steep rise in the reflection spectrum of vegetation, and as solar-induced fluorescence.

This study examined the detectability of biological fluorescence from two types of photosynthetic pigments, chlorophylls (Chls) and bacteriochlorophylls (BChls), on Earth-like planets with oxygen-rich/poor and anoxic atmospheres around the Sun and M dwarfs.

Atmospheric absorption, such as H2O, CH4, O2, and O3, and the VRE obscure the fluorescence emissions from Chls and BChls. We found that BChl-based fluorescence for wavelengths of 1000-1100 nm, assuming the spectrum of BChl b-bearing purple bacteria, could provide a suitable biosignature but only in the absence of the water cloud coverage or other strong absorbers near 1000 nm. The Chl fluorescence is weaker for several reasons, e.g., spectral blending with the VRE.

The apparent reflectance excess is greatly increased in both Chl and BChl cases around TRAPPIST-1 due to fluorescence and stellar absorption lines. This could be a promising feature for detecting the fluorescence around ultracool red dwarfs by follow-up ground-based observations with high spectral resolution; however, it requires a long time around Sun-like stars, even for a LUVOIR-like space mission.

Moreover, the simultaneous detection of fluorescence and VRE is key to identifying traces of photosynthesis because absorption, reflectance, and fluorescence are physically connected. For further validation of fluorescence detection, the nonlinear response of biological fluorescence as a function of light intensity could be considered.

Yu Komatsu, Yasunori Hori, Masayuki Kuzuhara, Makiko Kosugi, Kenji Takizawa, Norio Narita, Masashi Omiya, Eunchul Kim, Nobuhiko Kusakabe, Victoria Meadows, Motohide Tamura

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2301.03824 [astro-ph.EP] (or arXiv:2301.03824v1 [astro-ph.EP] for this version)
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Submission history
From: Yu Komatsu
[v1] Tue, 10 Jan 2023 07:42:43 UTC (4,086 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻