Extrasolar planetary systems made up of terrestrial-type planets in compact, tightly-spaced orbits are most likely to form around lower-metallicity stars, a new study concludes.

The study, just published in The Astrophysical Journal Letters, notes that such systems may be much more numerous than previously thought. They are also more likely to have formed early in the history of our cosmos. As a result, this would inherently give them more than enough time to have spawned stable life that would have had billions of years to evolve.

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