Atmospheric ozone and oxygen protect the biosphere of our planet against harmful ultraviolet radiation. In new research, astronomers modeled atmospheres of Earth-like exoplanets hosted by stars with near-solar temperatures — between 5300 and 6300 K — and a broad range of metallicities covering known exoplanet host stars; they found that paradoxically, although metal-rich stars emit substantially less ultraviolet radiation than metal-poor stars, the surface of their planets is exposed to more intense ultraviolet radiation.
Complex, multicellular life on land requires oxygen from which ozone forms, leading to a tolerable ultraviolet radiation level at the surface for its development and evolution.
Stellar emission and planetary ultraviolet protection depend on the effective temperature of the host star.
While for a young planet ultraviolet exposure can be essential for abiogenesis, high levels of ultraviolet light trigger genomic damage and are a threat to all life forms.
“We wanted to understand what properties a star must have in order for its planets to form a protective ozone layer,” said Dr. Anna Shapiro, an astronomer at the Max Planck Institute for Solar System Research.
“We saw huge peaks in intensity. It is therefore quite possible, that the Sun, too, is capable of such spikes in intensity. In that case, also the intensity of the ultraviolet light would increase dramatically.”
“So naturally we wondered, what this would mean for life on Earth and what the situation is like in other star systems,” added Dr. Sami Solanki, director at the Max Planck Institute for Solar System Research.
In their research, the authors investigated the dependence of planetary surface ultraviolet on the atmospheric concentration of oxygen and stellar metallicity for stars of three spectral types: G2V (5800 K, representing solar case), G5V (5300 K), and F7V (6300 K).
“In the Earth’s atmospheric chemistry, ultraviolet radiation from the Sun plays a…
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