Planets come in two families — and their stars decide which

Astronomers led by Diego Turrini at Italy's National Institute for Astrophysics compared hundreds of planetary systems and found they fall into two distinct families: wide, massive systems that are restless from birth, and tighter, calmer ones. Which family a system joins depends on how much planet-building material its star starts with. Published in Nature Astronomy, the finding gives planet-hunters a clearer map of where solar-system-like worlds — and perhaps habitable ones — are most likely to form.