Milky Way planetary systems fall into two 'families,' scientists find

Researchers at Italy's INAF studied 300 of the more than 1,000 known multiplanet systems in the Milky Way and identified two distinct families: wide, massive systems around stars heavier than the sun, and compact systems with similar-sized planets around sun-like stars. The study was published in Nature Astronomy.

• 300 multiplanet systems analyzed out of over 1,000 known
• First family: total mass 2–10 times the solar system, frequent giant collisions and ejections
• Second family: compact 'peas-in-a-pod' systems with orbits tighter than Mercury's
• Findings confirmed by simulations of planetary system evolution