The research, published on Tuesday in Nature Communications, analyzed the chemical composition of more than 3,000 stars and their planets, and found that low-metallicity systems—those with fewer elements heavier than hydrogen and helium—may have a higher chance of hosting life than previously thought.
The authors of the study, led by Anna Shapiro, an astrophysicist at Harvard University, used data from NASA’s Kepler mission and the European Space Agency’s Gaia mission to measure the metallicity of stars and their planets.
Metallicity is a key factor that influences the formation and evolution of planets, as well as the potential for life to emerge and thrive on them.
According to Shapiro, most of the planets discovered so far are around stars with high metallicity, similar to our Sun. This is because metal-rich stars tend to have more rocky planets, which are considered more suitable for life than gas giants.
However, this bias may also reflect the limitations of current detection methods, which favor finding planets around bright and nearby stars.
“I think this narrows the habitability zone a little bit,” said Anna Shapiro in a call with Motherboard that also included study co-author Alexander Shapiro, another astrophysicist at the Max Planck Institute for Solar System Research.
“Our research shows that finding life around metal-poor stars is more promising from the point of view of the radiative signature.”
One of the reasons for this surprising result is that low-metallicity stars are more likely to have planets in the habitable zone—the region around a star where liquid water can exist on the surface.
This is because low-metallicity stars tend to be smaller and cooler than high-metallicity stars, which means their habitable zones are closer and wider.
Another reason is that low-metallicity planets may have more favorable conditions for life to emerge and evolve. For instance, low-metallicity planets may have thinner atmospheres, which could protect them from harmful radiation and prevent runaway greenhouse effects.
Low-metallicity planets may also have more diverse chemistry, which could increase the chances of producing complex organic molecules—the building blocks of life.
Shapiro said that these findings have important implications for the search for extraterrestrial life, as they suggest that we should broaden our horizons and look for planets around a wider range of stars.
“While we should not neglect metal-rich systems like our own, we should also pay attention to metal-poor systems that may harbor a large number of potentially habitable planets,” she said. “We should also be open-minded about what kinds of planets can support life, as they may not look like Earth at all.”
Shapiro added that future missions such as NASA’s James Webb Space Telescope and the European Space Agency’s PLATO mission will be able to test these predictions and provide more insights into the diversity and distribution of life in the universe.