Milky Way planetary systems split into two evolutionary groups, study suggests

Astronomers examined roughly 300 well-characterized multiplanet systems in the Milky Way. They identified two broad families whose properties appear tied to the stars they orbit, shaping how the systems evolve and what happens to their planets. The findings may help guide the search for habitable exoplanets by clarifying which planetary systems are more likely to retain life-friendly worlds.

INAF-led researchers classified roughly 300 of the galaxy’s best-studied multiplanet systems. One family is wide and massive, with total planetary mass two to ten times the solar system’s; its planets circle stars heavier than the sun but poorer in elements beyond helium. The other family is compact and lighter, with similarly sized worlds orbiting stars no larger or more metal-rich than the sun, often closer than Mercury.

A key marker was planetary misalignment from a shared circular plane, which can record past gravitational violence such as collisions and ejections. Those disruptions were common in the first family and uncommon in the second. This link may help prioritize targets in the search for habitable worlds.