Biofluorescent Worlds II. Biological fluorescence induced by stellar UV flares, a new temporal biosignature

Abstract

Our first targets in the search for signs of life are orbiting nearby M stars, such as the planets in the Proxima Centauri, Ross-128, LHS-1140, and TRAPPIST-1 systems. Future ground-based discoveries, and those from the TESS mission, will provide additional close-by targets. However, young M stars tend to be very active, flaring frequently and causing UV fluxes on the surfaces of HZ planets to become biologically harmful. Common UV-protection methods used by life (e.g. living underground, or underwater) would make a biosphere harder to detect. However, photoprotective biofluorescence, 'up-shifting' UV to longer, safer wavelengths, could increase a biosphere's detectability. Here we model intermittent emission at specific wavelengths in the visible spectrum caused by biofluorescence as a new temporal biosignature for planets around active M stars. We use the absorption and emission characteristics of common coral fluorescent pigments and proteins to create model spectra and colours for an Earth-like planet in such a system, accounting for different surface features, atmospheric absorption, and cloud cover. We find that for a cloud-free planet biofluorescence could induce a temporary change in brightness that is significantly higher than the reflected flux alone, causing up to two orders-of-magnitude change in planet-star contrast, compared to a non-fluorescent state, if the surface is fully covered by a highly efficient fluorescent biosphere. Hence, UV-flare induced biofluorescence presents previously unexplored possibilities for a new temporal biosignature that could be detectable by instruments like those planned for the extremely large telescope and could reveal hidden biospheres.

Accepted for publication in MNRAS. 16 pages, 7 figures

References in corpus (31)

• Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1
• A terrestrial planet candidate in a temperate orbit around Proxima Centauri
• A seven-planet resonant chain in TRAPPIST-1
• A temperate rocky super-Earth transiting a nearby cool star
• Vegetation's Red Edge: A Possible Spectroscopic Biosignature of Extraterrestrial Plants
• A Re-appraisal of the Habitability of Planets Around M Dwarf Stars
• The Pale Orange Dot: The Spectrum and Habitability of Hazy Archean Earth
• The Habitability of Planets Orbiting M-dwarf Stars
• The habitability of Proxima Centauri b II. Possible climates and Observability
• How to Characterize Habitable Worlds and Signs of Life
• Atmospheric reconnaissance of the habitable-zone Earth-sized planets orbiting TRAPPIST-1
• Modeling Repeated M-dwarf Flaring at an Earth-like Planet in the Habitable Zone: I. Atmospheric Effects for an Unmagnetized Planet
• The Origin of RNA Precursors on Exoplanets
• A Statistical Reconstruction of the Planet Population Around Kepler Solar-Type Stars
• Exoplanet Biosignatures: Observational Prospects
• Strong XUV irradiation of the Earth-sized exoplanets orbiting the ultracool dwarf TRAPPIST-1
• UV Surface Environment of Earth-like Planets Orbiting FGKM Stars Through Geological Evolution
• Magnetospheric Structure and Atmospheric Joule Heating of Habitable Planets Orbiting M-dwarf Stars
• UV habitable zones around M stars
• Reconnaissance of the TRAPPIST-1 exoplanet system in the Lyman-$\alpha$ line
• Identifying the rotation rate and the presence of dynamic weather on extrasolar Earth-like planets from photometric observations
• A Volcanic Hydrogen Habitable Zone
• UV Surface Habitability of the TRAPPIST-1 System
• A temperate exo-Earth around a quiet M dwarf at 3.4 parsecs
• On the uncertain nature of the core of $\mathbf{\alpha }$ Cen A
• The Vegetation Red Edge Biosignature Through Time on Earth and Exoplanets
• The Pale Green Dot: A Method to Characterize Proxima Centauri b using Exo-Aurorae
• Lessons from early Earth: UV surface radiation should not limit the habitability of active M star systems
• Solar irradiance changes and phytoplankton productivity in Earth's ocean following astrophysical ionizing radiation events
• TESS Habitable Zone Star Catalog
• Biofluorescent Worlds I: Global Biological Fluorescence as a Biosignature

Cited by in corpus (12)

• How to Characterize Habitable Worlds and Signs of Life
• UV Surface Habitability of the TRAPPIST-1 System
• No Such Thing as a Simple Flare: Substructure and QPPs Observed in a Statistical Sample of 20 Second Cadence TESS Flares
• The Pale Green Dot: A Method to Characterize Proxima Centauri b using Exo-Aurorae
• ExoPlaSim: Extending the Planet Simulator for Exoplanets
• On the Orbital Inclination of Proxima Centauri b
• Starspots Modelling and Flare Analysis on Selected MV Stars
• In Search of the Edge: A Bayesian Exploration of the Detectability of Red Edges in Exoplanet Reflection Spectra
• Biosignature Surveys to Exoplanet Yields and Beyond
• High-resolution reflection spectra for Proxima b and Trappist-1e models for ELT observations
• Photosynthetic Fluorescence from Earth-Like Planets around Sun-Like and Cool Stars
• Hot Earth or Young Venus? A nearby transiting rocky planet mystery