Affiliation:
1. Carl Sagan Institute at Cornell University, Ithaca, NY 14853, USA
2. Astronomy Department, Cornell University, Ithaca, NY 14853, USA
Abstract
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.
Funder
Simons Foundation
Carl Sagan Institute at Cornell
Publisher
Oxford University Press (OUP)
Subject
Space and Planetary Science,Astronomy and Astrophysics
Cited by
9 articles.
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