Metal-poor stars are more “friendly” to life

Planets located in habitable zones around metal-poor stars are the best targets for the search for potential life beyond Earth, according to the study that researchers from two Max Planck Institutes (Germany) and other international centers publish this week in the journal Nature Communications.

The authors focused on metallicity, the abundance of elements heavier than hydrogen and helium in a star. Our Sun, where there are more than 31,000 atoms of hydrogen for every atom of iron, has served as a benchmark, considering stars rich in metals those with more than the Sun, and poor those with less.

Planets located in habitable zones around metal-poor stars are the best targets for the search for potential life beyond Earth.

They also verified that the amount of metals in a star is related to its ultraviolet radiation emissions and that this, in turn, in its two modalities (B and C) affects the ozone layer that the planets can generate.

“The key lies in the different distribution of energy in metal-rich and metal-poor stars towards their stellar atmospheres,” explains lead author Anna Shapiro of the Max Planck Institute for Solar System Research to SINC, “and that o The thickness of the ozone layer is proportional to the ratio between UV-C radiation (which produces ozone by photolysis of oxygen) and UV-B radiation (which destroys ozone).

“This relationship decreases with metallicity: it is greater in metal-poor stars than in rich ones”, underlines the researcher. In the first, UV-C radiation predominates, which allows the formation of a dense layer of ozone, protective of life.

In those with more metals, although they emit less UV radiation, UV-B prevails, associated with a scarcer and ineffective ozone envelope to sustain life.

The protection of the planetary atmosphere from harmful ultraviolet stellar radiation largely depends on the metallicity of the host star. /MPS/hormesdesign.de

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The researchers reached these conclusions after modeling the atmospheres of hypothetical Earth-like planets housed in stars with different metallicities, thus confirming that worlds located around metal-poor stars are the ones with the highest UV protection, which has implications for the search for potential life beyond our planet.

This discovery could be useful for future space missions, such as the mission DISH of the European Space Agency (ESA), which from 2026 will search a wide range of stars in search of signs of habitable exoplanets.

Increasingly difficult scenario for life

Furthermore, the study reaches a paradoxical conclusion: as the universe ages, it is likely to become increasingly hostile to life. Metals and other heavy elements form inside stars at the end of their multi-billion-year lives and, depending on their mass, are released into space in the form of stellar winds or supernova explosions. They are the building material for the next generation of stars.

The study reaches an almost paradoxical conclusion: as the universe ages, it is likely to become increasingly hostile to life.

“So each newly formed star has more metal-rich building material available than its predecessors: stars in the universe are becoming more metal-rich with each generation,” says Shapiro.

According to the authors, the probability of stellar systems producing life also decreases as the universe ages. However, their search outside Earth is not in vain.

After all, many stars that host exoplanets are similar in age to the Sun, and we know that our star is home to complex and interesting life forms on at least one of its planets.

Reference:

Anna V. Shapiro et al. “Stars rich in metals are less suitable for the evolution of life on their planets”. Nature Communications, 2023.

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