Four of the solar system's terrestrial planets, including Earth and a long-lost world, likely started life waltzing around the sun to a fixed rhythm, according to a new study. The findings also suggest that those planets formed earlier than previously thought.
Astronomers have been increasingly interested in how planetary systems change their internal architecture on cosmic timescales, motivated by several recent exoplanet family discoveries, like the seven-planet cohort orbiting the tiny star TRAPPIST-1.
