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Abstract EANA2024-95 |
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Impact of biological feedbacks on the habitability of rocky exoplanets
Erica Bisesi (1,2), Giuseppe Murante (1,2,3), Antonello Provenzale (2), Laura Silva (1,3), Michele Maris (1,3), Nicoletta La Rocca (4,1), Mariano Battistuzzi (4,5)
(1) INAF − Astronomical Observatory of Trieste, Italy
(2) CNR − Institute of Geosciences and Earth Resources, Pisa, Italy
(3) SISSA − Institute for Fundamental Physics of the Universe, Trieste, Italy
(4) Department of Biology, University of Padova, Italy
(5) INAF − Astronomical Observatory of Arcetri, Florence, Italy
The study of exoplanetary climates plays a crucial role in Astrobiology, the science that investigates the origin, evolution and distribution of life in the Universe. The climate of a rocky planet is of paramount importance to establish the possible presence of liquid water at its surface, and thus, in the wide sense generally accepted by the Astronomical community, its habitability.
On Earth, a well-known regulator of planetary climate is its vegetation cover. Vegetation can modify the planetary surface albedo via the Charney mechanism, as plants are usually darker than the bare surface of the continents. We updated ESTM (Earth-like Surface Temperature Model) to incorporate the presence, distribution and evolution of two dynamically competing vegetation types that resemble grasslands and trees (the latter in the double stages of life: adults and seedlings). The newly developed model was applied to estimate how the climate-vegetation system reaches equilibrium across different rocky planetary configurations, and to assess its impact on temperature and habitability. With respect to a world with bare granite continents, the effect of vegetation-albedo feedback is to increase the average surface temperature. Since grasses and trees exhibit different albedos, they affect temperature to different degrees. The ultimate impact on climate depends on the outcome of the competition between these vegetation types. The change in albedo due to vegetation extends the habitable zone and enhances the overall planetary habitability beyond its traditional outer edge. This effect is especially relevant for planets that have a larger extension of continents than Earth.
This also illustrates the transition from a snowball state to an habitable planet at the outer edge of the circumstellar habitability zone. Before the Cambrian, continents on Earth did not have a vegetation cover and their albedo could have been as high as that of granite (0.35). Being lower, vegetation albedo can increase the planetary surface’ temperature, thus reducing the probability of runaway ice-albedo feedback. We are using ESTM to compute the surface temperature of Earth, as it was 660 Myr ago, within a grid of different continental albedos which account for both bare continental soil and different vegetation types (Bisesi et al., work in progress).
Additionally, we are interested in the conditions for the survival of several and competing species of cyanobacteria and microalgae in the habitable circumstellar zone of M stars. With this aim we will consider: i) data selected from literature about the photosynthetic performances of cyanobacteria in habitats characterized by light spectra resembling those generated by M stars, such as caves, soils or microbial mats; ii) data coming from theoretical studies; iii) data obtained by experiments carried out by exposing different strains of cyanobacteria to simulated M stars spectra (Battistuzzi et al., 2023).
