For some exoplanets, just being in the Goldilocks zone isn’t enough. Planets need to be made up of the right stuff to become a cradle of life, new research suggests.

Planets composed of certain element cocktails can’t host a continual recycling of Earth-like tectonic plates, new simulations of exoplanet interiors indicate. Measuring the compositions of stars could help astronomers narrow the list of potentially habitable planets, said Cayman Unterborn, who presented the work December 18 at the American Geophysical Union’s fall meeting.

“This is a new way of thinking — astronomers don’t think in geology terms,” said Unterborn, an extrasolar planetary scientist at Ohio State University. Exoplanet hunters currently treat an exoplanet as potentially habitable if it falls the right distance from its sun for water to exist in liquid form.

“When we talk about habitable planets, it may not be wise to just say Goldilocks zone — there may be a Goldilocks composition as well,” Unterborn said.

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