Metal-rich stars inhibit chances of life on their planets
They give off less UV, but more is absorbed by their planets’ atmospheres, boffins tell life hunters
Scientists hoping to narrow down the hunt for life outside of our solar system have hit on an indicator that may guide the search: metal.
Specifically, the number of elements heavier than hydrogen or helium in the planetary systems’ host star. Although relatively metal-rich stars emit comparatively less UV radiation, more is likely to make it to the planet's surface as a result of the development of the atmosphere.
High levels of UV radiation are known to cause genomic damage in life forms. Here on Earth, we’re protected by much of the Sun’s UV by the ozone layer and atmospheric oxygen.
To maximise the likelihood of finding signatures of life, planets hosted by low-metallicity stars discovered by these instruments should be priority targets...
A team led by Anna Shapiro, a postdoctoral researcher at the Max-Planck Institute for Solar System Research, has been experimenting with computational models of the metallic make-up of stars and their impact on planets within their orbit.
They found that although metal-rich stars emit substantially less UV radiation than metal-poor stars, the surface of their associated planets is exposed to more intense UV radiation, according to a paper published in Nature Communications this week.
“For the stellar types considered, metallicity has a larger impact than stellar temperature. During the evolution of the universe, newly formed stars have progressively become more metal rich, exposing organisms to increasingly intense ultraviolet radiation. Our findings imply that planets hosted by stars with low metallicity are the best targets to search for complex life on land,” the paper said.
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The researchers said a new generation of radial velocity spectrometers will detect the wobble in distant stars caused by planets with greater accuracy than ever before, helping discover Earth-like planets in the habitable zones of Sun-like stars. The objective is shared by PLAnetary Transits and Oscillations (PLATO) of stars space telescope, set for launch in 2026.
“Our results indicate that to maximise the likelihood of finding signatures of life, planets hosted by low-metallicity stars discovered by these instruments should be priority targets of the follow-up observations with future telescopes,” the researchers said.
In January last year, scientists found that life on so-called Super-Earths — exoplanets with a bigger mass than Earth but below that of Uranus and Neptune — may have more time to develop and evolve, thanks to their long-lasting magnetic fields protecting them against harmful cosmic rays. ®