Photosynthetic Fluorescence from Earth-Like Planets around Sun-Like and Cool Stars

Abstract

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.

References in corpus (22)

• Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life
• Biosignatures from Earth-Like Planets Around M Dwarfs
• The MUSCLES Treasury Survey I: Motivation and Overview
• Vegetation's Red Edge: A Possible Spectroscopic Biosignature of Extraterrestrial Plants
• Spectral signatures of photosynthesis I: Review of Earth organisms
• Exoplanet Biosignatures: Understanding Oxygen as a Biosignature in the Context of Its Environment
• Spectral Evolution of an Earth-Like Planet
• Spectral signatures of photosynthesis II: coevolution with other stars and the atmosphere on extrasolar worlds
• Evolved Climates and Observational Discriminants for the TRAPPIST-1 Planetary System
• Vegetation signature in the observed globally-integrated spectrum of Earth: Modeling the red edge strength using simultaneous cloud data and application for extrasolar planets
• Nonphotosynthetic Pigments as Potential Biosignatures
• Characterizing Rocky and Gaseous Exoplanets with 2-meter Class Space-based Coronagraphs
• Spectra of Earth-like Planets Through Geological Evolution Around FGKM Stars
• Observations of the Near-Infrared Spectrum of the Zodiacal Light with CIBER
• Nitrogen Dioxide Pollution as a Signature of Extraterrestrial Technology
• Characterizing the purple Earth: Modelling the globally-integrated spectral variability of the Archean Earth
• Ultraviolet to optical diffuse sky emission as seen by the Hubble Space Telescope Faint Object Spectrograph
• Red-edge position of habitable exoplanets around M-dwarfs
• The peak absorbance wavelength of photosynthetic pigments around other stars from spectral optimization
• Biofluorescent Worlds I: Global Biological Fluorescence as a Biosignature
• Biofluorescent Worlds II. Biological fluorescence induced by stellar UV flares, a new temporal biosignature
• Oxidation of the Interiors of Carbide Exoplanets