Astronomers could boost the efficiency of the search for alien worlds that might harbour life by using a technique that can help determine whether a star has already eaten its planets.
at the Astronomical Observatory of Padua, Italy, and his colleagues analysed a series of binary stars – pairs of stars that orbit one another. Because both stars in a binary pair typically formed from a single giant molecular cloud, they should be chemically identical.
“However, we’ve known for a long time that there are some anomalous cases,” says Spina.
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Astronomers had speculated that this chemical divergence could be explained if one star in the pair ate a planet it hosted – changing its chemical make-up. However, until now, we had no idea how common this phenomenon might be.
Spina and his team looked at 107 binary star pairs that all had stars with similar masses and temperatures to our sun. Using a statistical model, they found that 27 per cent of the stars in their sample were likely to have eaten one or more planet.
In binary systems with such a star, not only did the two stars have a different chemical composition, but one in each pair was far richer in elements like iron that could only be derived from ingesting rocky planets.
The team also found that the temperature of the star affected its make-up in a way that is best explained by planet engulfment. The hotter the star, the more likely it was to have a different composition to its partner.
“This is because when the star is hotter, its outer layer is even thinner,” says Spina. “This means that even the ingestion of a planet the size of Earth can affect the chemical composition of that star.” The thinner the star’s outer layer, or convective zone, the worse it is at diluting a planet’s materials – and so the star’s atmosphere will better reflect the contaminants.
Knowing the chemical signature of planet-eating stars means we can more quickly discount them as potential hosts for Earth-like worlds. “We’re alive today because we live in a very peaceful and quiet solar system,” says Spina.
at the University of Cambridge says the findings are “certainly interesting”. But he notes that they cannot be directly applied to single stars like our sun because binary stars are more likely to engage in planet engulfment. “Nevertheless, understanding the formation of these systems… is crucial for understanding planet formation and the origin of life in the universe,” he says.
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