Planetary genealogy: Milky Way worlds belong to 1 of 2 ‘families,’ scientists find

Scientists have discovered that planetary systems in the Milky Way belong to two distinct families that shape their evolution and survival. Researchers at the Italian National Institute for Astrophysics studied 300 well-understood multiplanet systems to understand how infant stellar environments affect planetary fates. The first family features wide, massive systems with total masses between two and 10 times that of our solar system.

These planets orbit stars that are heavier than the sun and contain lower concentrations of elements heavier than hydrogen and helium. The second family consists of compact, lower-mass systems with comparable planet sizes and tight orbits around stars that match or fall below the sun's mass and metallicity.

Researchers used planetary orbital deviations as a genetic marker to trace a history of violent gravitational instability, such as giant collisions and ejections. Turbulence was common in the first family but rare in the second. Simulations indicated that the first group is unstable from birth because excess material makes the planets too large to remain stable.

Team member Camilla Danielski stated that the analysis proved these structural diversities are real rather than observational illusions.

The findings were published on October 13 in Nature Astronomy.