Three years ago, researchers led by the Max Planck Institute for Solar System research had compared the Sun's brightness variations with those of hundreds of Sun-like stars. 'We wanted to understand what properties a star must have in order for its planets to form a protective ozone layer,' Anna Shapiro, scientist at the Max Planck Institute for Solar System Research and first author of the current study, explains the basic idea.Īs often in science, this idea was triggered by an earlier finding. A protective layer of ozone is thus an important prerequisite for the emergence of complex life. As on Earth, this compound of three oxygen atoms can protect the planet's surface (and life forms residing on it) from cell-damaging ultraviolet (UV) radiation. With the help of numerical simulations, the current study, which was published in Nature Communications today, now turns to the ozone content of exoplanet atmospheres. Do observational data show evidence of an atmosphere? Does it perhaps even contain gases such as oxygen or methane, which on Earth are produced almost exclusively as metabolic products of lifeforms? In the next years, such observations will be pushed to new limits: Nasa’s James Webb Telescope will make it possible to not only characterize the atmospheres of large gas giants like Super-Neptunes, but also to analyze for the first time the much fainter spectrographic signals from rocky planet atmospheres.

In the search for habitable or even inhabited planets orbiting distant stars, researchers have in the past years increasingly focused on the gas envelopes of these worlds. It also suggests a startling conclusion: as the universe ages, it becomes increasingly unfriendly to the emergence of complex life on new planets. The study provides scientists searching the sky with space telescopes for habitable star systems with important clues as to where this endeavour could be particularly promising. Crucial to this is the intensity of the ultraviolet light that the star emits into space, in different wavelength ranges. The team showed how the metallicity of a star is connected to the ability of its planets to surround themselves with a protective ozone layer. Stars that contain comparatively large amounts of heavy elements provide less favourable conditions for the emergence of complex life than metal-poor stars, as scientists from the Max Planck Institutes for Solar System Research and for Chemistry as well as from the University of Göttingen have now found.

A cosmology of monsters